Association of Continued Breastfeeding with Micronutrient Status, Thyroid Function, and Cognitive Development in Toddlers

Association of Continued Breastfeeding with Micronutrient Status, Thyroid Function, and Cognitive Development in Toddlers | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Association of Continued Breastfeeding with Micronutrient Status, Thyroid Function, and Cognitive Development in Toddlers Shu-Chi Mu, Sing-Chung Li, Yi-Fang Liu, Yi-Ling Chen, Li-Yi Tsai, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7553779/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Background : To investigate the associations of continued breastfeeding with micronutrient status, thyroid function, and cognitive development in toddlers. Methods: In this cross-sectional study, 110 toddlers aged 1–2 years were recruited at Shin Kong Wu Ho-Su Memorial Hospital. Participants were categorized into continued breastfeeding (CBF) and discontinued breastfeeding (DCBF) groups. Data collection included anthropometry and Bayley-III cognitive evaluation. Laboratory analyses measured complete blood count, ferritin, 25(OH)D₃, calcium, PTH, TSH, FT3, FT4, and urinary iodine concentration. Results: Toddlers in the CBF group had significantly lower ferritin levels and a higher prevalence of iron deficiency compared with the DCBF group (p < 0.05), while vitamin D insufficiency and suboptimal iodine status were common across both groups. Thyroid hormone profiles of all participants were within normal ranges, but FT4 concentrations were higher in the CBF group ( p = 0.001) and were positively associated with cognitive, language, and motor scores on the Bayley-III (all p < 0.05). Multivariable regression further confirmed FT4 as a significant predictor of developmental outcomes, whereas male sex predicted lower language performance. Conclusion: Continued breastfeeding was associated with improved cognitive outcomes, potentially mediated by higher FT4 concentrations, but also increased risk of iron deficiency. These findings highlight the need to encourage breastfeeding while ensuring appropriate micronutrient monitoring and supplementation, particularly iron and vitamin D, to optimize toddler development. Figures Figure 1 Figure 2 Background Breastfeeding provides substantial benefits for infants, mothers, and society at large. Human milk supplies the optimal balance of nutrients and bioactive components essential for infant growth and development, while also conferring protection against infectious diseases such as respiratory and gastrointestinal infections, as well as reducing the risk of otitis media and sudden infant death syndrome. Beyond early life, breastfeeding has been associated with lower risks of obesity, type 2 diabetes, asthma, and cardiovascular disease, and it contributes positively to neurocognitive development [ 1 , 2 ]. For mothers, breastfeeding facilitates postpartum recovery by promoting uterine involution and reducing postpartum hemorrhage, and it is associated with long-term health benefits including decreased risks of breast and ovarian cancers, type 2 diabetes, and cardiovascular disease [ 3 ]. Furthermore, breastfeeding fosters maternal–infant bonding and may lower the incidence of postpartum depression. At a societal level, breastfeeding reduces healthcare expenditures by preventing illness, decreases reliance on infant formula, and contributes to environmental sustainability [ 4 ]. Exclusive breastfeeding is recommended for the first six months of life; however, if breast milk remains the major source of nutrition beyond this period without the timely introduction of complementary foods, infants are at increased risk of multiple nutrient deficiencies. The most critical shortfall is iron, since the iron content of breast milk, though highly bioavailable, is insufficient to meet the elevated demands of infants after six months, thereby predisposing them to iron-deficiency anemia [ 5 , 6 ]. Zinc intake may also become inadequate due to the declining concentration of zinc in breast milk over time, which can impair growth and immune function if not supplemented by complementary foods such as meat or eggs [ 7 ]. Furthermore, vitamin D is naturally present in breast milk only in low amounts, and in the absence of supplementation or adequate sunlight exposure, infants may develop rickets and poor bone mineralization [ 8 , 9 ]. Vitamin B12 deficiency is another concern, particularly among infants of vegetarian or B12-deficient mothers, as it can compromise neurological development [ 10 ]. In addition to micronutrient insufficiencies, breast milk alone may not provide adequate energy and protein to sustain the rapid growth occurring during late infancy, potentially resulting in growth faltering and developmental delays [ 5 ]. Adequate micronutrient intake during early childhood is critical for optimal growth and neurodevelopment, yet toddlers who continue to rely predominantly on breast milk without appropriate complementary foods are at increased risk of several nutrient deficiencies. Iron deficiency is among the most prevalent and is consistently associated with impaired cognitive, language, and motor development, as well as long-lasting effects on learning and behavior, even after treatment [ 11 , 12 ]. Zinc is another limiting nutrient in breast milk after six months; deficiency during toddlerhood has been linked to poorer attention, psychomotor function, and overall cognitive performance [ 13 , 14 ]. Vitamin D insufficiency, common in breastfed infants and toddlers with limited sun exposure, may contribute to rickets and has been associated with suboptimal neuropsychological outcomes in early childhood [ 15 , 16 ]. Similarly, inadequate vitamin B12 intake, particularly in children of vegetarian or B12-deficient mothers, has been shown to impair neurological development, memory, and executive function [ 17 , 18 ]. In addition, iodine deficiency, one of the most widespread preventable causes of intellectual disability globally, can severely compromise thyroid function and lead to reduced IQ and impaired school performance when inadequately addressed in early life [ 19 – 21 ]. Collectively, these findings highlight that, beyond six months of age, continued breastfeeding without the timely introduction of nutrient-dense complementary foods may predispose toddlers to multiple micronutrient deficiencies that have detrimental and often irreversible effects on cognitive and neurodevelopmental outcomes. In Taiwan, limited nutritional surveys have been conducted among toddlers, and evidence regarding the long-term effects of continued breastfeeding on nutritional status and cognitive development is scarce. While numerous international studies have highlighted potential nutrient inadequacies and their consequences for child development, there is a lack of region-specific data to determine whether these findings apply to Taiwanese children, who may have distinct dietary patterns and cultural practices. Addressing this gap is crucial for informing infant and young child feeding policies and for guiding parents and healthcare providers in optimizing child nutrition. Therefore, the present study aims to investigate the relationship between prolonged breastfeeding, nutritional status, and cognitive development in toddlers in Taiwan. Materials and methods Study design This cross-sectional study was conducted in the Department of Pediatrics at Shin Kong Hospital between February 2019 and December 2020. Toddlers aged 1–2 years who attended routine vaccination visits were recruited. Data collected included maternal characteristics (age, educational level, employment status, and breastfeeding status) and child characteristics (age, sex, gestational age at birth, and birth weight). Anthropometric measurements of the toddlers were taken as indicators of growth and development. Blood and urine samples were collected to determine biochemical markers and nutritional status. Cognitive development was assessed using the Bayley Scales of Infant and Toddler Development, Third Edition (Bayley-III), to examine the relationship between nutritional status and cognitive outcomes. Participant Recruitment Participants were recruited from the Department of Pediatrics, Shin Kong Hospital. Eligible subjects were healthy toddlers aged 1–2 years. Exclusion criteria included a history of preterm birth (gestational age < 37 weeks), congenital disorders, gastrointestinal diseases, cardiac diseases, hepatic or renal diseases, and infectious diseases. The study protocol was explained to the legal guardians of all potential participants, and written informed consent was obtained prior to enrollment. The study was approved by the Institutional Review Board of Shin Kong Hospital (IRB No. 20180901R). Anthropometric Measurements Anthropometric measurements were performed using a hospital-calibrated stadiometer and scale to assess height and weight. Head circumference was measured with a non-stretchable plastic measuring tape, placed above the eyebrows and around the most prominent part of the occiput. All measurements were converted into percentiles based on the Taiwan Child Growth Standards issued by the Ministry of Health and Welfare. Biochemical Measurements Venous blood samples (3 mL) were collected by trained personnel and divided into two tubes: one containing EDTA for complete blood count (CBC) analysis and one without anticoagulant for serum biochemical assays. Samples were delivered to Chung-Yi Medical Laboratory on the day of collection or the following day for analysis. CBC was measured using an automated hematology analyzer (XN10, Sysmex, Japan). Serum concentrations of 25(OH)D₃ and parathyroid hormone (PTH) were determined using chemiluminescent immunoassays (Roche Cobas 6000, Germany), with intra-assay CVs of 4.52% and 1.43%, and inter-assay CVs of 7.63% and 2.90%, respectively. Serum calcium was measured using the Beckman Coulter calcium (oCPC) assay kit (o-Cresolpthalein complexone method) with absorbance read on a Roche Cobas 8000 analyzer (Germany), yielding an intra-assay CV of 1.03% and an inter-assay CV of 1.43%. Ferritin and thyroid hormones (TSH, FT3, FT4) were analyzed by electrochemiluminescence immunoassays on a fully automated analyzer (Roche Cobas 6000, Germany). The intra- and inter-assay CVs for ferritin were 4.98% and 9.72%, respectively. The intra-assay CVs for TSH, FT3, and FT4 were 2.27%, 2.57%, and 2.58%, respectively, with corresponding inter-assay CVs of 4.57%, 6.07%, and 3.54%. For urinary analysis, 3 mL of urine was collected for the determination of urinary iodine concentration (UIC) using the method recommended by the EQUIP (Ensuring the Quality of Urinary Iodine Procedures) program of the U.S. Centers for Disease Control and Prevention (CDC). UIC was analyzed with the modified ammonium persulfate digestion on microplate method (APDM), followed by the Sandell–Kolthoff reaction, with both intra- and inter-assay CVs < 5%. Cognitive Development Assessment Cognitive development was evaluated using the Bayley Scales of Infant and Toddler Development, Third Edition (Bayley-III). The assessment was administered by a licensed clinical psychologist and included evaluation of cognitive, receptive language, expressive language, fine motor, and gross motor development. The Bayley-III is an internationally standardized instrument designed to assess developmental functioning in children aged 1–42 months, and it has been widely validated for use in both clinical and research settings. Raw scores were converted into composite scores based on age-specific norms, providing a reliable and comprehensive measure of early developmental status. Statistical Analysis All statistical analyses were performed using SPSS version 22.0 (IBM Corp., Armonk, NY, USA). The Kolmogorov–Smirnov test was applied to assess the normality of data distribution. Continuous variables were expressed as mean ± standard deviation (SD) for normally distributed data or as median (interquartile range, IQR) for non-normally distributed data. Group comparisons were conducted using independent Student’s t -test for normally distributed variables and the Mann–Whitney U test for non-normally distributed variables. Categorical variables were presented as frequencies and percentages [ n (%)], and differences between groups were assessed using the chi-square test. Correlations were examined using Pearson correlation analysis. To identify potential predictors of child development across cognitive, motor, and language domains, multivariable linear regression analyses were performed. Composite scores for cognition, motor, and language were used as dependent variables, while serum FT4, FT3, 25(OH)D₃, hemoglobin, ferritin, age at assessment (months), and sex were included as independent variables. A two-tailed p value < 0.05 was considered statistically significant. Results Study Flow A total of 722 toddlers aged 1–2 years were screened for eligibility at the Department of Pediatrics, Shin Kong Wu Ho-Su Memorial Hospital. Of these, 145 were excluded due to prematurity (n = 77), severe colds (n = 62), congenital heart disease (n = 3), DiGeorge’s disease (n = 1), or Kawasaki disease (n = 2), leaving 577 eligible participants. Among them, 427 declined to participate, and 150 were enrolled. During the study, 38 participants were further excluded, including 33 who withdrew consent, 1 due to blood draw failure, 1 who refused cognitive assessment, 2 with urine collection failures, and 1 with incomplete dietary data. A total of 112 participants completed the study, of which 2 were excluded due to elevated TSH levels (> 10 µIU/mL) in order to minimize the potential confounding effects of overt thyroid dysfunction. Finally, 110 toddlers were included in the data analysis, with 27 in the continued breastfeeding (CBF) group and 83 in the discontinued breastfeeding (DCBF) group. Characteristics of mothers and toddlers Among the 110 toddlers included, 27 were in the continued breastfeeding (CBF) group and 83 in the discontinued breastfeeding (DCBF) group. Characteristics of mothers and toddlers was presented in Table 1 . Maternal characteristics did not significantly differ between groups in terms of age and education; however, a higher proportion of mothers in the CBF group were homemakers compared with the DCBF group ( p = 0.049). No significant group differences were observed in toddlers’ chronological age, sex distribution, birth weight, or gestational age at birth. Anthropometric measures were generally comparable between groups, except for head circumference and head circumference percentile, which were significantly lower in the CBF group ( p = 0.017). Table 1 Characteristics of mothers and toddlers by breastfeeding status Variables All (N = 110) CBF group ( N = 27) DCBF group (N = 83) p value Mothers Age (year) 0.566 < 30 17 (15.5) 3 (11.1) 14 (16.9) 30–39 81 (73.6) 22 (81.5) 59 (71.1) ≧ 40 12 (10.9) 2 (7.4) 10 (12.0) Education 0.094 Under high school 17 (15.5) 1 (3.7) 16 (19.3) Collage 81 (73.6) 24 (88.9) 57 (68.7) Master and above 12 (10.9) 2 (7.4) 10 (12.0) Working state 0.049 * Homemaking 47 (43) 17 (63.0) 30 (36.1) Full-time 49 (45) 8 (29.6) 41 (49.4) Part-time 14 (13) 2 (7.4) 12 (14.5) Toddlers chronological age (year) 1.5 (0.77) 1.5 (0.4) 1.5 (0.8) 0.417 Sex 0.331 Male 59 (54) 13 (48) 46 (55) Female 51 (46) 14 (52) 37 (45) Birth weight (kg) 3.0 (0.6) 3.0 (0.4) 3.0 (0.7) 0.464 Gestational age at birth (weeks) 39.0 (1.0) 39.0 (1.0) 38.0 (2) 0.351 Anthropometric Height (cm) 82.2 (6.5) 81.5 (6.0) 82.4 (6.4) 0.179 Weight (kg) 10.5 (2.3) 10.5 (1.9) 10.4 (2.3) 0.564 Head circumference (cm) 47.0 (2.1) 46.0 (2.2) 47.0 (2.5) 0.017 * BMI (kg/m 2 ) 15.4 (1.8) 15.6 (1.6) 15.3 (2.0) 0.403 Height percentile (%) 49.0 (51.8) 32.3 (61.1) 52.0 (47.7) 0.245 Weight percentile (%) 43.2 (41.6) 44.8 (27.7) 41.2 (44.6) 0.972 Head circumference percentile (%) 44.0 (54.9) 27.0 (36.6) 50.2 (52.4) 0.017 * Values are presented as mean ± SD, median (IQR), or n (%). CBF group, continued breastfeeding at enrollment; DCBF group, discontinued breastfeeding at enrollment; BMI, body mass index. Independent Student’s t -test or Mann–Whitney U test was used for continuous variables, and chi-square test for categorical variables. * p < 0.05 was considered statistically significant. Different feeding types on the nutritional status of toddlers As shown in Table 2 , there were no significant group differences in hemoglobin concentration, vitamin D status (25(OH)D₃, PTH, calcium), or urinary iodine indices between the CBF and DCBF groups. However, serum ferritin levels were significantly lower in toddlers who continued breastfeeding compared with those who had discontinued breastfeeding ( p < 0.001). The prevalence of vitamin D insufficiency or deficiency did not significantly differ between groups. However, iron deficiency was more common among toddlers in the CBF group compared with the DCBF group (22% vs. 5%, p = 0.022). Urinary iodine (UI) excretion in spot urine samples is the easiest method to assess iodine deficiency. A median urinary iodine excretion less than 100 µg/L in a population indicates iodine deficiency [ 22 ]. Although 28% of toddlers had urinary iodine concentrations below 100 µg/L, no significant differences were observed in the prevalence of iodine deficiency or excess between the CBF and DCBF groups. (Table 3 ). Table 2 Effect of different feeding types on the nutritional status of toddlers Variables All (N = 110) CBF group ( N = 27) DCBF group (N = 83) p value Iron status HGB (g/dL) 12.5 ± 0.9 12.2 ± 1.0 12.5 ± 0.9 0.130 Ferritin (ng/mL) 37.6 (24.0) 22.9 (31.6) 40.7 (19.9) < 0.001 * Vitamin D status 25(OH)D 3 (ng/mL) 27.6 ± 6.4 26.2 ± 7.3 28.0 ± 6.1 0.206 PTH (pg/mL) 19.2 (11.6) 18.9 (11.1) 19.6 (12.2) 0.865 Ca (mg/dL) 10.2 ± 0.3 10.3 ± 0.3 10.2 ± 0.3 0.359 Iodine status UIC (µg/L) 195 (238) 204 (211) 184 (265) 0.898 Values are presented as mean ± SD or median (interquartile range, IQR). CBF group, continued breastfeeding at enrollment; DCBF group, discontinued breastfeeding at enrollment; HGB, hemoglobin; PTH, parathyroid hormone; UIC, Urinary Iodine Concentration. p values were calculated using the Mann–Whitney U test for non-normally distributed variables or Student’s t -test for normally distributed variables. *p < 0.05 was considered statistically significant. Table 3 Prevalence of vitamin D, iron and iodine deficiency in toddlers All (N = 110) CBF group ( N = 27) DCBF group (N = 83) p value Vitamin D nutritional status a 0.093 Sufficient 40 (36) 9 (33) 31 (37) Insufficient 58 (53) 12 (44) 46 (55) Deficiency 12 (11) 6 (22) 6 (7) Iron nutritional status b 0.022 * Normal 100 (91) 21 (78) 79 (95) Iron deficiency 8 (7) 5 (19) 3 (4) Iron deficiency anemia 2 (2) 1 (4) 1 (1) Iodine nutritional status c 0.577 Excessive 35 (32) 8 (30) 27 (33) Adequate 44 (40) 13 (48) 31 (37) Deficiency 31 (28) 6 (22) 25 (30) Values are expressed as n (%). CBF group, continued breastfeeding at enrollment; DCBF group, discontinued breastfeeding at enrollment. ᵃ Vitamin D sufficient: 25(OH)D₃ ≥ 30 ng/mL; insufficient: 25(OH)D₃ 20–29 ng/mL; deficiency: 25(OH)D₃ < 20 ng/mL. ᵇ Normal: ferritin ≥ 12 ng/mL and hemoglobin ≥ 11 g/dL; iron deficiency (ID): ferritin < 12 ng/mL and hemoglobin ≥ 11 g/dL; iron deficiency anemia (IDA): ferritin < 12 ng/mL and hemoglobin < 11 g/dL. ᶜ Excessive: urinary iodine concentration (UIC) ≥ 300 µg/L; adequate: 100–299 µg/L; deficiency: < 100 µg/L. *p values calculated using chi-square test. p < 0.05 was considered statistically significant. Cognitive development of toddlers The results of cognitive development of toddlers was presented in Table 4 . Toddlers in the CBF group had significantly higher median composite scores and percentile ranks in both cognitive and language domains compared with those in the DCBF group ( p < 0.05 for all). No significant group differences were observed in motor development. Table 4 Cognitive development of toddlers All (N = 110) CBF group ( N = 27) DCBF group (N = 83) p value Composite Score Cognitive 105 (15) 110 (10) 105 (15) 0.021 * Language 100 (21) 106 (15) 100 (20) 0.029 * Motor 107 (10) 107 (12) 103 (13) 0.153 Percentile Rank Cognitive 63 (34) 75 (21) 63 (38) 0.024 * Language 50 (52) 66 (34) 50 (52) 0.030 * Motor 68 (25) 68 (29) 58 (33) 0.139 Values are presented as median (interquartile range). CBF group, continued breastfeeding at enrollment; DCBF group, discontinued breastfeeding at enrollment. *p values were calculated using the Mann–Whitney U test. p < 0.05 was considered statistically significant. Thyroid function of toddlers Because thyroid disorders may affect cognitive development in children, two toddlers with abnormally elevated TSH levels were excluded from the analysis. Thus, all participants included in the final dataset had thyroid function values within the normal reference range. As shown in Table 5 , subtle differences in thyroid function were observed between groups. Serum TSH and FT3 levels did not differ significantly; however, FT4 concentrations were significantly higher in the CBF group compared with the DCBF group ( p = 0.001). As illustrated in Fig. 2 , FT4 concentrations were positively correlated with cognitive (r = 0.298, p = 0.002), language (r = 0.290, p = 0.002), and motor (r = 0.367, p < 0.001) composite scores, suggesting that higher FT4 levels may contribute to better neurodevelopmental performance in toddlers. In contrast, serum FT3 concentrations showed no significant correlations with cognitive function scores. Although FSH exhibited a negative trend with cognition, the association did not reach statistical significance (data not shown). Table 5 Thyroid function of toddlers All (N = 110) CBF group ( N = 27) DCBF group (N = 83) p value TSH (µIU/mL) ab 3.29 ± 1.65 3.46 ± 1.57 3.23 ± 1.69 0.534 FT3 (pg/mL) 4.35 ± 0.52 4.51 ± 0.48 4.30 ± 0.52 0.078 FT4 (ng/dL) 1.32 ± 0.14 1.40 ± 0.11 1.29 ± 0.14 0.001 * Values are expressed as mean ± SD. CBF group, continued breastfeeding at enrollment; DCBF group, discontinued breastfeeding at enrollment; TSH, thyroid-stimulating hormone; FT3, free triiodothyronine; FT4, free thyroxine. *p values were calculated using independent Student’s t-test. p < 0.05 was considered statistically significant. ᵃ Reference range for TSH in toddlers: approximately 0.7–5.97 µIU/mL. ᵇ TSH, thyroid-stimulating hormone; FT3, free triiodothyronine; FT4, free thyroxine. Since vitamin D, iron status, and thyroid function may influence cognitive function in young children, a multivariable linear regression analyses were further conducted to identify predictors of developmental outcomes. The results demonstrated that higher FT4 levels were significantly associated with better cognitive, language, and motor composite scores on the Bayley-III ( p < 0.01). In contrast, higher serum 25(OH)D₃ concentrations were negatively associated with cognitive scores ( p = 0.013). Sex was an additional predictor of language development, with males exhibiting lower language scores ( p = 0.006), while age at assessment showed a borderline positive association with language outcomes ( p = 0.054). Other variables, including FT3, hemoglobin, and ferritin, were not significantly associated with developmental domains. (Table 6 ). Table 6 Multiple linear regression predicting cognitive, motor, and language composite scores Outcome Predictor B (β) 95% CI p-value Cognition FT4 (ng/dL) 22.98 (0.29) 8.60–37.35 0.002* FT3 (pg/mL) -3.78 (-0.17) -7.85–0.28 0.071 25(OH)D3 (ng/mL) -0.42 (-0.24) -0.74–-0.09 0.013* HGB (g/dL) 0.80 (0.07) -1.33–2.94 0.463 Ferritin (ng/mL) -0.02 (-0.07) -0.08–0.04 0.486 Age (month) 0.07 (0.03) -0.37–0.51 0.761 Sex -2.19 (-0.10) -6.33–1.95 0.302 Language FT4 (ng/dL) 26.40 (0.27) 8.50–44.31 0.005* FT3 (pg/mL) -3.43 (-0.12) -8.50–1.63 0.187 25(OH)D3 (ng/mL) -0.11 (-0.05) -0.51–0.29 0.593 HGB (g/dL) -0.96 (-0.06) -3.62–1.70 0.479 Ferritin (ng/mL) -0.02 (-0.05) -0.10–0.06 0.591 Age (month) 0.55 (0.18) -0.00–1.10 0.054 Sex -7.32 (-0.26) -12.47–-2.17 0.006* Motor FT4 (ng/dL) 21.85 (0.37) 10.88–32.83 < 0.001* FT3 (pg/mL) -0.88 (-0.05) -3.98–2.22 0.579 25(OH)D3 (ng/mL) -0.07 (-0.05) -0.32–0.18 0.574 HGB (g/dL) 0.04 (0.01) -1.59–1.68 0.957 Ferritin (ng/mL) -0.01 (-0.03) -0.06–0.04 0.746 Age (month) -0.19 (-0.10) -0.53–0.15 0.275 Sex -1.72 (-0.10) -4.87–1.44 0.289 Values are unstandardized coefficients (B) with standardized β in parentheses. CI = confidence interval. Sex was coded as male = 1, female = 0. *p < 0.05 was considered statistically significant. Discussion In this cross-sectional study of toddlers aged 1–2 years, we investigated the impact of continued breastfeeding on nutritional status and cognitive development. The main findings were that toddlers in the continued breastfeeding (CBF) group had lower ferritin concentrations and a higher prevalence of iron deficiency compared with those who had discontinued breastfeeding (DCBF). In contrast, vitamin D and iodine status did not differ significantly between groups. Notably, despite the overall normal range of thyroid function, FT4 concentrations were higher in the CBF group, and FT4—but not FT3—was positively correlated with cognitive, language, and motor development scores. These results suggest that continued breastfeeding beyond infancy may influence both nutritional biomarkers and neurodevelopmental outcomes in early childhood. In our study, toddlers who continued breastfeeding had significantly lower ferritin levels and a higher prevalence of iron deficiency compared with those who had discontinued breastfeeding. This finding is consistent with previous reports suggesting that breast milk alone may not provide sufficient iron beyond six months of age, thereby increasing the risk of iron deficiency and anemia if complementary foods are inadequate[ 23 , 24 ] [ 25 ]. Iron deficiency has been widely associated with impaired cognitive, behavioral, and psychomotor development, largely due to its critical role in neurotransmitter synthesis and myelination [ 26 , 27 ]. However, when we compared the cognitive outcomes of toddlers with iron deficiency or iron-deficiency anemia to those with normal iron status, no significant differences were observed (data not shown). This may be explained by the fact that our participants did not present with severe anemia, which is often required to manifest measurable impairments in cognitive development. Therefore, while iron deficiency remains an important concern during early childhood, our findings suggest that mild or early-stage deficiency may not exert an immediate or detectable impact on cognitive outcomes. Vitamin D plays an essential role in skeletal growth, calcium homeostasis, and brain development through its involvement in neurotrophic signaling and neuronal differentiation. Previous studies have reported mixed findings regarding the impact of early-life vitamin D status on neurodevelopment. For example, a study in a slum-dwelling infant population found that higher serum 25(OH)D was associated with better temperament, language, and behavioral outcomes, though not with cognitive or motor domains [ 28 ]. Conversely, a longitudinal cohort in North India reported that vitamin D deficiency during early childhood was not linked to cognitive development or linear growth at school age [ 29 ]. These inconsistent findings underscore the need for further investigation into how vitamin D status influences specific domains of child neurodevelopment. In our cohort, more than 60% of toddlers had either insufficient or deficient vitamin D status, highlighting a common nutritional concern in early childhood. Although we did not find significant differences in vitamin D levels between toddlers who continued breastfeeding and those who had discontinued, the overall prevalence of insufficiency suggests that dietary intake and limited sunlight exposure may contribute to suboptimal vitamin D status in this age group. Previous studies have associated low vitamin D with impaired cognitive and language development, though the evidence remains inconsistent. Thus, vitamin D insufficiency in early life warrants attention, even if its impact on neurodevelopment was not clearly demonstrated in our population. Iodine is a critical component of thyroid hormone synthesis, and its deficiency during early childhood has been linked to irreversible neurodevelopmental impairment [ 30 , 31 ]. In our study, although 22% of toddlers in the CBF group and 30% in the DCBF group had urinary iodine concentrations below 100 µg/L, their thyroid hormone profiles remained within the normal range. Notably, FT4 concentrations were significantly higher in the CBF group compared with the DCBF group, suggesting that continued breastfeeding may exert a modest influence on thyroid function, even in the absence of overt iodine deficiency. Thyroid hormones play a pivotal role in early brain development, particularly in neuronal proliferation, synaptogenesis, and myelination. Among these, free thyroxine (FT4) acts as a critical substrate for local conversion to the biologically active FT3 within neural tissues, emphasizing its importance in neurodevelopment [ 32 ]. While extensive studies underscore the detrimental impact of clinically low thyroid hormone levels, emerging evidence suggests that even subtle variations in FT4 within the normal range may be biologically meaningful. In our study, FT4—but not FT3—demonstrated significant positive correlations with cognitive, language, and motor development in toddlers. This aligns with findings from Meng et al., who conducted a meta-analysis showing that children with neurological disorders exhibited notably lower FT4 levels than healthy controls, although TSH remained unaffected [ 33 ]. Moreover, Taylor's review outlined that early hypothyroidism, often associated with insufficient FT4, can lead to impaired cognitive function [ 34 ]. Collectively, these findings underscore the notion that FT4 may serve as a more sensitive marker of neurodevelopmental integrity in early childhood compared to other thyroid parameters. Monitoring subtle FT4 fluctuations—even those within the normative range—could thus provide valuable insights into the thyroid–brain developmental axis. While our findings suggest breastfeeding may be associated with subtle elevations in FT4 among toddlers, current literature indicates that human milk contains only minimal levels of thyroid hormones that are unlikely to alter infant thyroid function. According to LactMed, levothyroxine (T4) is present in human milk at trace concentrations (typically < 100 µg/L), with limited transfer and negligible clinical effects [ 35 ]. Consistent with earlier findings, Mizuta et al. reported undetectable T4 (including FT4) in breast milk and no significant differences in infant serum thyroid profiles between breastfed and formula-fed groups [ 36 , 37 ]. Overall, this suggests that the elevated FT4 observed in our study is more likely attributable to endogenous thyroid activity rather than exogenous hormone ingestion via breast milk. Several cohort studies demonstrate beneficial associations between prolonged breastfeeding and cognitive development. For instance, the Korean MOCEH cohort found that infants breastfed for ≥ 9 months scored significantly higher on the Mental Development Index at ages 1 through 3 years, with a clear dose–response pattern in regression models [ 38 ]. Similarly, children breastfed for more than 3 months exhibited superior communication, problem-solving, expressive language, and vocabulary inference abilities compared to those breastfed for shorter periods [ 39 ]. More recent evidence reinforces these findings: toddlers breastfed for at least 6 months demonstrated fewer developmental delays in milestone attainment [ 40 ], and prolonged breastfeeding has also been associated with greater cortical thickness, enhanced white-matter myelination, and better executive function into early adolescence [ 41 ]. Belfort and colleagues emphasized that breastfeeding supports brain development not only through nutrient supply but also through enhanced mother–infant interaction [ 42 ]. Consistent with these studies, our findings also showed that continued breastfeeding was associated with better cognitive development in toddlers. To our knowledge, this is among the few studies to simultaneously demonstrate the pathway linking breastfeeding with thyroid function and neurodevelopment. Specifically, our findings suggest that prolonged breastfeeding is associated with higher FT4 concentrations, which in turn correlate positively with cognitive performance. This integrated observation provides novel evidence that FT4 may serve as a mediating biomarker between breastfeeding practices and improved cognitive outcomes in toddlers, thereby offering a new perspective on the biological mechanisms underlying the neurodevelopmental benefits of continued breastfeeding. From a clinical and public health perspective, these results highlight the importance of promoting continued breastfeeding while also monitoring thyroid-related biomarkers, as this dual approach may help optimize both nutritional adequacy and neurodevelopmental outcomes in early childhood. Moreover, the potential risk of iron deficiency and iron-deficiency anemia associated with prolonged breastfeeding should not be overlooked. Clinicians are advised to encourage continued breastfeeding while simultaneously monitoring the iron status of toddlers to prevent adverse outcomes. In addition, the high prevalence of vitamin D insufficiency observed in our cohort, regardless of breastfeeding status, represents another important nutritional concern that warrants attention in early childhood. This study has several limitations that should be acknowledged. First, its cross-sectional design precludes causal inference regarding the relationships among breastfeeding, nutritional status, thyroid function, and cognitive development. Second, the sample size was relatively small and derived from a single medical center, which may limit the generalizability of the findings to other populations. Third, although no significant differences were observed in maternal and child baseline characteristics, the potential influence of unmeasured confounders—such as home stimulation, parental intelligence, and genetic factors—cannot be excluded. Finally, cognitive development was assessed using the Bayley-III at a single time point, which may not fully capture long-term neurodevelopmental trajectories. Future studies employing larger, longitudinal cohorts with repeated developmental assessments are warranted to clarify the causal pathways linking prolonged breastfeeding, micronutrient status, thyroid function, and neurodevelopment. Moreover, mechanistic research is needed to better understand how subtle variations in thyroid hormones, particularly FT4, may mediate the cognitive benefits of breastfeeding. Conclusions In summary, this study demonstrated that continued breastfeeding in toddlers was associated with lower ferritin levels and a higher prevalence of iron deficiency, underscoring the importance of timely introduction of iron-rich complementary foods. Vitamin D insufficiency was highly prevalent regardless of breastfeeding status, highlighting another critical nutritional concern in early childhood. Although no significant differences in iodine deficiency were observed between groups, subtle variations in thyroid function were noted, with toddlers who continued breastfeeding exhibiting higher FT4 concentrations. Importantly, FT4 levels were positively correlated with cognitive, language, and motor development, suggesting a potential biological pathway linking breastfeeding with neurodevelopmental outcomes. Taken together, these findings indicate that while prolonged breastfeeding may confer cognitive benefits, careful monitoring of micronutrient status, particularly iron and vitamin D, remains essential to ensure optimal growth and development in toddlers. From a clinical perspective, these results emphasize the need to encourage continued breastfeeding while simultaneously providing appropriate nutritional monitoring and supplementation strategies to maximize both health and developmental outcomes. Abbreviations CBF, continued breastfeeding; DCBF, discontinued breastfeeding; CBC, complete blood count; PTH, parathyroid hormone; TSH, thyroid-stimulating hormone; FT3, free triiodothyronine; FT4, free thyroxine; UIC, urinary iodine concentration; Bayley-III, Bayley Scales of Infant and Toddler Development, Third Edition. Declarations Acknowledgements The authors would like to express their sincere gratitude to all the toddlers and their parents for participating in this study. We also acknowledge the dedicated support of the pediatric staff and clinical psychologist Chia-wen Chang at Shin Kong Wu Ho-Su Memorial Hospital for their invaluable assistance with participant recruitment, sample collection, and cognitive assessments. Funding information This study was funded by Shin Kong Wu Ho-Su Memorial Hospital (grant number 2019SKHADR021 and 2020SKHADR024). Author contribution Shu-Chi Mu: Writing – original draft, Project administration, Investigation, Formal analysis Sing-Chung Li: Writing – original draft, Visualization, Resources, Methodology, Formal analysis Yi-Fang Liu: Writing –review & editing, Urinary iodine analysis Yi-Ling Chen: Writing –review & editing Project administration, Li-Yi Tsai: Writing –review & editing, Project administration Huei-Ting Kuo: Cognitive development assessment Zi-Ying Chen: Project administration, Visualization Chiao-Ming Chen: Writing–review & editing, Writing–original draft, Visualization, Supervision, Project administration, Methodology, Investigation, Formal analysis, Conceptualization. Ethics approval and consent to participate The study was approved by the Institutional Review Board of Shin-Kong Wu Ho-Su Memorial Hospital (IRB no. 20180901R). The approved study period was from January 2019 to December 2020. Consent for publication Not applicable Data availability The datasets used and analyzed during the current study are available from the corresponding author on reasonable request. Competing interests The authors declare no competing interests. References Victora CG, Bahl R, Barros AJ, França GV, Horton S, Krasevec J, Murch S, Sankar MJ, Walker N, Rollins NC: Breastfeeding in the 21st century: epidemiology, mechanisms, and lifelong effect . Lancet 2016, 387 (10017):475-490. Horta BL, Loret de Mola C, Victora CG: Long-term consequences of breastfeeding on cholesterol, obesity, systolic blood pressure and type 2 diabetes: a systematic review and meta-analysis . Acta Paediatr 2015, 104 (467):30-37. Chowdhury R, Sinha B, Sankar MJ, Taneja S, Bhandari N, Rollins N, Bahl R, Martines J: Breastfeeding and maternal health outcomes: a systematic review and meta-analysis . Acta Paediatr 2015, 104 (467):96-113. World Health Organization (WHO). Infant and young child feeding: Fact sheet. 2023. 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Kim SY, et al.: Longer breastfeeding is associated with improved neurodevelopmental outcomes in early childhood: Evidence from a Korean birth cohort . International Breastfeeding Journal 2020, 15 :51. Goldshtein I, et al.: Breastfeeding duration and risk of developmental delay in early childhood . JAMA Network Open 2025, 8 (1):e2831869. Ottino González J, Fernández MAR, Esaian S, Rajagopalan V, Bouhrara M, Goran MI, Adise S: Sustained breastfeeding associations with brain structure and cognition from late childhood to early adolescence . Pediatr Res 2025. Belfort MB: Breastfeeding, brain development, and beyond . Current Opinion in Pediatrics 2017, 29 (2):177-184. Additional Declarations No competing interests reported. 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1","display":"","copyAsset":false,"role":"figure","size":83971,"visible":true,"origin":"","legend":"\u003cp\u003eFlowchart of study\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7553779/v1/eeb273212d99c2dd7efeb99d.png"},{"id":91832166,"identity":"daa2386f-afc0-4572-b03a-fbe4d5a323ba","added_by":"auto","created_at":"2025-09-22 09:18:25","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":25380,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelations between serum FT4 (free thyroxine) concentrations and neurodevelopmental outcomes.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7553779/v1/b9322de980528d91bbd57881.png"},{"id":91838129,"identity":"ebec8085-f1be-44ae-a011-cf4366234bc7","added_by":"auto","created_at":"2025-09-22 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Human milk supplies the optimal balance of nutrients and bioactive components essential for infant growth and development, while also conferring protection against infectious diseases such as respiratory and gastrointestinal infections, as well as reducing the risk of otitis media and sudden infant death syndrome. Beyond early life, breastfeeding has been associated with lower risks of obesity, type 2 diabetes, asthma, and cardiovascular disease, and it contributes positively to neurocognitive development [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. For mothers, breastfeeding facilitates postpartum recovery by promoting uterine involution and reducing postpartum hemorrhage, and it is associated with long-term health benefits including decreased risks of breast and ovarian cancers, type 2 diabetes, and cardiovascular disease [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Furthermore, breastfeeding fosters maternal\u0026ndash;infant bonding and may lower the incidence of postpartum depression. At a societal level, breastfeeding reduces healthcare expenditures by preventing illness, decreases reliance on infant formula, and contributes to environmental sustainability [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eExclusive breastfeeding is recommended for the first six months of life; however, if breast milk remains the major source of nutrition beyond this period without the timely introduction of complementary foods, infants are at increased risk of multiple nutrient deficiencies. The most critical shortfall is iron, since the iron content of breast milk, though highly bioavailable, is insufficient to meet the elevated demands of infants after six months, thereby predisposing them to iron-deficiency anemia [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Zinc intake may also become inadequate due to the declining concentration of zinc in breast milk over time, which can impair growth and immune function if not supplemented by complementary foods such as meat or eggs [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Furthermore, vitamin D is naturally present in breast milk only in low amounts, and in the absence of supplementation or adequate sunlight exposure, infants may develop rickets and poor bone mineralization [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Vitamin B12 deficiency is another concern, particularly among infants of vegetarian or B12-deficient mothers, as it can compromise neurological development [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. In addition to micronutrient insufficiencies, breast milk alone may not provide adequate energy and protein to sustain the rapid growth occurring during late infancy, potentially resulting in growth faltering and developmental delays [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eAdequate micronutrient intake during early childhood is critical for optimal growth and neurodevelopment, yet toddlers who continue to rely predominantly on breast milk without appropriate complementary foods are at increased risk of several nutrient deficiencies. Iron deficiency is among the most prevalent and is consistently associated with impaired cognitive, language, and motor development, as well as long-lasting effects on learning and behavior, even after treatment [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Zinc is another limiting nutrient in breast milk after six months; deficiency during toddlerhood has been linked to poorer attention, psychomotor function, and overall cognitive performance [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Vitamin D insufficiency, common in breastfed infants and toddlers with limited sun exposure, may contribute to rickets and has been associated with suboptimal neuropsychological outcomes in early childhood [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Similarly, inadequate vitamin B12 intake, particularly in children of vegetarian or B12-deficient mothers, has been shown to impair neurological development, memory, and executive function [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. In addition, iodine deficiency, one of the most widespread preventable causes of intellectual disability globally, can severely compromise thyroid function and lead to reduced IQ and impaired school performance when inadequately addressed in early life [\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Collectively, these findings highlight that, beyond six months of age, continued breastfeeding without the timely introduction of nutrient-dense complementary foods may predispose toddlers to multiple micronutrient deficiencies that have detrimental and often irreversible effects on cognitive and neurodevelopmental outcomes.\u003c/p\u003e\u003cp\u003eIn Taiwan, limited nutritional surveys have been conducted among toddlers, and evidence regarding the long-term effects of continued breastfeeding on nutritional status and cognitive development is scarce. While numerous international studies have highlighted potential nutrient inadequacies and their consequences for child development, there is a lack of region-specific data to determine whether these findings apply to Taiwanese children, who may have distinct dietary patterns and cultural practices. Addressing this gap is crucial for informing infant and young child feeding policies and for guiding parents and healthcare providers in optimizing child nutrition. Therefore, the present study aims to investigate the relationship between prolonged breastfeeding, nutritional status, and cognitive development in toddlers in Taiwan.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003eStudy design\u003c/p\u003e\u003cp\u003eThis cross-sectional study was conducted in the Department of Pediatrics at Shin Kong Hospital between February 2019 and December 2020. Toddlers aged 1\u0026ndash;2 years who attended routine vaccination visits were recruited. Data collected included maternal characteristics (age, educational level, employment status, and breastfeeding status) and child characteristics (age, sex, gestational age at birth, and birth weight). Anthropometric measurements of the toddlers were taken as indicators of growth and development. Blood and urine samples were collected to determine biochemical markers and nutritional status. Cognitive development was assessed using the Bayley Scales of Infant and Toddler Development, Third Edition (Bayley-III), to examine the relationship between nutritional status and cognitive outcomes.\u003c/p\u003e\u003cp\u003eParticipant Recruitment\u003c/p\u003e\u003cp\u003eParticipants were recruited from the Department of Pediatrics, Shin Kong Hospital. Eligible subjects were healthy toddlers aged 1\u0026ndash;2 years. Exclusion criteria included a history of preterm birth (gestational age\u0026thinsp;\u0026lt;\u0026thinsp;37 weeks), congenital disorders, gastrointestinal diseases, cardiac diseases, hepatic or renal diseases, and infectious diseases. The study protocol was explained to the legal guardians of all potential participants, and written informed consent was obtained prior to enrollment. The study was approved by the Institutional Review Board of Shin Kong Hospital (IRB No. 20180901R).\u003c/p\u003e\u003cp\u003eAnthropometric Measurements\u003c/p\u003e\u003cp\u003eAnthropometric measurements were performed using a hospital-calibrated stadiometer and scale to assess height and weight. Head circumference was measured with a non-stretchable plastic measuring tape, placed above the eyebrows and around the most prominent part of the occiput. All measurements were converted into percentiles based on the Taiwan Child Growth Standards issued by the Ministry of Health and Welfare.\u003c/p\u003e\u003cp\u003eBiochemical Measurements\u003c/p\u003e\u003cp\u003eVenous blood samples (3 mL) were collected by trained personnel and divided into two tubes: one containing EDTA for complete blood count (CBC) analysis and one without anticoagulant for serum biochemical assays. Samples were delivered to Chung-Yi Medical Laboratory on the day of collection or the following day for analysis. CBC was measured using an automated hematology analyzer (XN10, Sysmex, Japan). Serum concentrations of 25(OH)D₃ and parathyroid hormone (PTH) were determined using chemiluminescent immunoassays (Roche Cobas 6000, Germany), with intra-assay CVs of 4.52% and 1.43%, and inter-assay CVs of 7.63% and 2.90%, respectively. Serum calcium was measured using the Beckman Coulter calcium (oCPC) assay kit (o-Cresolpthalein complexone method) with absorbance read on a Roche Cobas 8000 analyzer (Germany), yielding an intra-assay CV of 1.03% and an inter-assay CV of 1.43%. Ferritin and thyroid hormones (TSH, FT3, FT4) were analyzed by electrochemiluminescence immunoassays on a fully automated analyzer (Roche Cobas 6000, Germany). The intra- and inter-assay CVs for ferritin were 4.98% and 9.72%, respectively. The intra-assay CVs for TSH, FT3, and FT4 were 2.27%, 2.57%, and 2.58%, respectively, with corresponding inter-assay CVs of 4.57%, 6.07%, and 3.54%.\u003c/p\u003e\u003cp\u003eFor urinary analysis, 3 mL of urine was collected for the determination of urinary iodine concentration (UIC) using the method recommended by the EQUIP (Ensuring the Quality of Urinary Iodine Procedures) program of the U.S. Centers for Disease Control and Prevention (CDC). UIC was analyzed with the modified ammonium persulfate digestion on microplate method (APDM), followed by the Sandell\u0026ndash;Kolthoff reaction, with both intra- and inter-assay CVs\u0026thinsp;\u0026lt;\u0026thinsp;5%.\u003c/p\u003e\u003cp\u003eCognitive Development Assessment\u003c/p\u003e\u003cp\u003eCognitive development was evaluated using the Bayley Scales of Infant and Toddler Development, Third Edition (Bayley-III). The assessment was administered by a licensed clinical psychologist and included evaluation of cognitive, receptive language, expressive language, fine motor, and gross motor development. The Bayley-III is an internationally standardized instrument designed to assess developmental functioning in children aged 1\u0026ndash;42 months, and it has been widely validated for use in both clinical and research settings. Raw scores were converted into composite scores based on age-specific norms, providing a reliable and comprehensive measure of early developmental status.\u003c/p\u003e\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eStatistical Analysis\u003c/h2\u003e\u003cp\u003eAll statistical analyses were performed using SPSS version 22.0 (IBM Corp., Armonk, NY, USA). The Kolmogorov\u0026ndash;Smirnov test was applied to assess the normality of data distribution. Continuous variables were expressed as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD) for normally distributed data or as median (interquartile range, IQR) for non-normally distributed data. Group comparisons were conducted using independent Student\u0026rsquo;s \u003cem\u003et\u003c/em\u003e-test for normally distributed variables and the Mann\u0026ndash;Whitney U test for non-normally distributed variables. Categorical variables were presented as frequencies and percentages [\u003cem\u003en\u003c/em\u003e (%)], and differences between groups were assessed using the chi-square test. Correlations were examined using Pearson correlation analysis. To identify potential predictors of child development across cognitive, motor, and language domains, multivariable linear regression analyses were performed. Composite scores for cognition, motor, and language were used as dependent variables, while serum FT4, FT3, 25(OH)D₃, hemoglobin, ferritin, age at assessment (months), and sex were included as independent variables. A two-tailed p value\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e\u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eStudy Flow\u003c/p\u003e\u003cp\u003eA total of 722 toddlers aged 1\u0026ndash;2 years were screened for eligibility at the Department of Pediatrics, Shin Kong Wu Ho-Su Memorial Hospital. Of these, 145 were excluded due to prematurity (n\u0026thinsp;=\u0026thinsp;77), severe colds (n\u0026thinsp;=\u0026thinsp;62), congenital heart disease (n\u0026thinsp;=\u0026thinsp;3), DiGeorge\u0026rsquo;s disease (n\u0026thinsp;=\u0026thinsp;1), or Kawasaki disease (n\u0026thinsp;=\u0026thinsp;2), leaving 577 eligible participants. Among them, 427 declined to participate, and 150 were enrolled. During the study, 38 participants were further excluded, including 33 who withdrew consent, 1 due to blood draw failure, 1 who refused cognitive assessment, 2 with urine collection failures, and 1 with incomplete dietary data.\u003c/p\u003e\u003cp\u003eA total of 112 participants completed the study, of which 2 were excluded due to elevated TSH levels (\u0026gt;\u0026thinsp;10 \u0026micro;IU/mL) in order to minimize the potential confounding effects of overt thyroid dysfunction. Finally, 110 toddlers were included in the data analysis, with 27 in the continued breastfeeding (CBF) group and 83 in the discontinued breastfeeding (DCBF) group.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eCharacteristics of mothers and toddlers\u003c/p\u003e\u003cp\u003eAmong the 110 toddlers included, 27 were in the continued breastfeeding (CBF) group and 83 in the discontinued breastfeeding (DCBF) group. Characteristics of mothers and toddlers was presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Maternal characteristics did not significantly differ between groups in terms of age and education; however, a higher proportion of mothers in the CBF group were homemakers compared with the DCBF group (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.049). No significant group differences were observed in toddlers\u0026rsquo; chronological age, sex distribution, birth weight, or gestational age at birth. Anthropometric measures were generally comparable between groups, except for head circumference and head circumference percentile, which were significantly lower in the CBF group (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.017).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eCharacteristics of mothers and toddlers by breastfeeding status\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eVariables\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAll\u003c/p\u003e\u003cp\u003e\u003cem\u003e(N\u003c/em\u003e\u0026thinsp;=\u0026thinsp;110)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCBF group\u003c/p\u003e\u003cp\u003e(\u003cem\u003eN\u003c/em\u003e\u0026thinsp;=\u0026thinsp;27)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eDCBF group\u003c/p\u003e\u003cp\u003e\u003cem\u003e(N\u003c/em\u003e\u0026thinsp;=\u0026thinsp;83)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003ep\u003c/em\u003e value\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eMothers\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAge (year)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.566\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u0026lt; 30\u003c/p\u003e \u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e17 (15.5)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3 (11.1)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e14 (16.9)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e30\u0026ndash;39\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e81 (73.6)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e22 (81.5)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e59 (71.1)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e≧ 40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e12 (10.9)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2 (7.4)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e10 (12.0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEducation\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.094\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eUnder high school\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e17 (15.5)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1 (3.7)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e16 (19.3)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCollage\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e81 (73.6)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e24 (88.9)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e57 (68.7)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMaster and above\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e12 (10.9)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2 (7.4)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e10 (12.0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eWorking state\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.049 *\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHomemaking\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e47 (43)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e17 (63.0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e30 (36.1)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFull-time\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e49 (45)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e8 (29.6)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e41 (49.4)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePart-time\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e14 (13)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2 (7.4)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e12 (14.5)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eToddlers\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003echronological age (year)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.5 (0.77)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1.5 (0.4)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1.5 (0.8)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.417\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSex\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.331\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMale\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e59 (54)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e13 (48)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e46 (55)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFemale\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e51 (46)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e14 (52)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e37 (45)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBirth weight (kg)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e3.0 (0.6)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e3.0 (0.4)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3.0 (0.7)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.464\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGestational age at birth (weeks)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e39.0 (1.0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e39.0 (1.0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e38.0 (2)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.351\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAnthropometric\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHeight (cm)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e82.2 (6.5)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e81.5 (6.0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e82.4 (6.4)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.179\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eWeight (kg)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10.5 (2.3)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e10.5 (1.9)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e10.4 (2.3)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.564\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHead circumference (cm)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e47.0 (2.1)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e46.0 (2.2)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e47.0 (2.5)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.017 *\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBMI (kg/m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e15.4 (1.8)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e15.6 (1.6)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e15.3 (2.0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.403\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHeight percentile (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e49.0 (51.8)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e32.3 (61.1)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e52.0 (47.7)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.245\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eWeight percentile (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e43.2 (41.6)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e44.8 (27.7)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e41.2 (44.6)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.972\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHead circumference percentile (%)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e44.0 (54.9)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e27.0 (36.6)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e50.2 (52.4)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.017 *\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eValues are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD, median (IQR), or n (%). CBF group, continued breastfeeding at enrollment; DCBF group, discontinued breastfeeding at enrollment; BMI, body mass index. Independent Student\u0026rsquo;s \u003cem\u003et\u003c/em\u003e-test or Mann\u0026ndash;Whitney U test was used for continuous variables, and chi-square test for categorical variables.\u003c/p\u003e\u003cp\u003e*\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e\u003cp\u003eDifferent feeding types on the nutritional status of toddlers\u003c/p\u003e\u003cp\u003eAs shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, there were no significant group differences in hemoglobin concentration, vitamin D status (25(OH)D₃, PTH, calcium), or urinary iodine indices between the CBF and DCBF groups. However, serum ferritin levels were significantly lower in toddlers who continued breastfeeding compared with those who had discontinued breastfeeding (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e\u003cp\u003eThe prevalence of vitamin D insufficiency or deficiency did not significantly differ between groups. However, iron deficiency was more common among toddlers in the CBF group compared with the DCBF group (22% vs. 5%, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.022). Urinary iodine (UI) excretion in spot urine samples is the easiest method to assess iodine deficiency. A median urinary iodine excretion less than 100 \u0026micro;g/L in a population indicates iodine deficiency [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Although 28% of toddlers had urinary iodine concentrations below 100 \u0026micro;g/L, no significant differences were observed in the prevalence of iodine deficiency or excess between the CBF and DCBF groups. (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eEffect of different feeding types on the nutritional status of toddlers\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eVariables\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAll\u003c/p\u003e\u003cp\u003e\u003cem\u003e(N\u003c/em\u003e\u0026thinsp;=\u0026thinsp;110)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCBF group\u003c/p\u003e\u003cp\u003e(\u003cem\u003eN\u003c/em\u003e\u0026thinsp;=\u0026thinsp;27)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eDCBF group\u003c/p\u003e\u003cp\u003e\u003cem\u003e(N\u003c/em\u003e\u0026thinsp;=\u0026thinsp;83)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003ep\u003c/em\u003e value\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eIron status\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHGB (g/dL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e12.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e12.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e12.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.130\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFerritin (ng/mL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e37.6 (24.0)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e22.9 (31.6)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e40.7 (19.9)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001 *\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eVitamin D status\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e25(OH)D\u003csub\u003e3\u003c/sub\u003e (ng/mL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e27.6\u0026thinsp;\u0026plusmn;\u0026thinsp;6.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e26.2\u0026thinsp;\u0026plusmn;\u0026thinsp;7.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e28.0\u0026thinsp;\u0026plusmn;\u0026thinsp;6.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.206\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePTH (pg/mL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e19.2 (11.6)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e18.9 (11.1)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e19.6 (12.2)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.865\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCa (mg/dL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e10.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e10.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.359\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eIodine status\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eUIC (\u0026micro;g/L)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e195 (238)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e204 (211)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e184 (265)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.898\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eValues are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD or median (interquartile range, IQR). CBF group, continued breastfeeding at enrollment; DCBF group, discontinued breastfeeding at enrollment; HGB, hemoglobin; PTH, parathyroid hormone; UIC, Urinary Iodine Concentration. \u003cem\u003ep\u003c/em\u003e values were calculated using the Mann\u0026ndash;Whitney U test for non-normally distributed variables or Student\u0026rsquo;s \u003cem\u003et\u003c/em\u003e-test for normally distributed variables.\u003c/p\u003e\u003cp\u003e\u003cem\u003e*p\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003ePrevalence of vitamin D, iron and iodine deficiency in toddlers\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAll\u003c/p\u003e\u003cp\u003e\u003cem\u003e(N\u003c/em\u003e\u0026thinsp;=\u0026thinsp;110)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCBF group\u003c/p\u003e\u003cp\u003e(\u003cem\u003eN\u003c/em\u003e\u0026thinsp;=\u0026thinsp;27)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eDCBF group\u003c/p\u003e\u003cp\u003e\u003cem\u003e(N\u003c/em\u003e\u0026thinsp;=\u0026thinsp;83)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003ep\u003c/em\u003e value\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eVitamin D nutritional status\u003c/b\u003e \u003csup\u003e\u003cb\u003ea\u003c/b\u003e\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.093\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSufficient\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e40 (36)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e9 (33)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e31 (37)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eInsufficient\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e58 (53)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e12 (44)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e46 (55)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDeficiency\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e12 (11)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e6 (22)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e6 (7)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eIron nutritional status\u003c/b\u003e \u003csup\u003e\u003cb\u003eb\u003c/b\u003e\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.022 *\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNormal\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e100 (91)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e21 (78)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e79 (95)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eIron deficiency\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e8 (7)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5 (19)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e3 (4)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eIron deficiency anemia\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e2 (2)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1 (4)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e1 (1)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eIodine nutritional status\u003c/b\u003e \u003csup\u003e\u003cb\u003ec\u003c/b\u003e\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.577\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eExcessive\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e35 (32)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e8 (30)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e27 (33)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAdequate\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e44 (40)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e13 (48)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e31 (37)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDeficiency\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e31 (28)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e6 (22)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e25 (30)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eValues are expressed as n (%). CBF group, continued breastfeeding at enrollment; DCBF group, discontinued breastfeeding at enrollment.\u003c/p\u003e\u003cp\u003eᵃ Vitamin D sufficient: 25(OH)D₃ \u0026ge; 30 ng/mL; insufficient: 25(OH)D₃ 20\u0026ndash;29 ng/mL; deficiency: 25(OH)D₃ \u0026lt; 20 ng/mL.\u003c/p\u003e\u003cp\u003eᵇ Normal: ferritin\u0026thinsp;\u0026ge;\u0026thinsp;12 ng/mL and hemoglobin\u0026thinsp;\u0026ge;\u0026thinsp;11 g/dL; iron deficiency (ID): ferritin\u0026thinsp;\u0026lt;\u0026thinsp;12 ng/mL and hemoglobin\u0026thinsp;\u0026ge;\u0026thinsp;11 g/dL; iron deficiency anemia (IDA): ferritin\u0026thinsp;\u0026lt;\u0026thinsp;12 ng/mL and hemoglobin\u0026thinsp;\u0026lt;\u0026thinsp;11 g/dL.\u003c/p\u003e\u003cp\u003eᶜ Excessive: urinary iodine concentration (UIC)\u0026thinsp;\u0026ge;\u0026thinsp;300 \u0026micro;g/L; adequate: 100\u0026ndash;299 \u0026micro;g/L; deficiency: \u0026lt; 100 \u0026micro;g/L.\u003c/p\u003e\u003cp\u003e\u003cem\u003e*p\u003c/em\u003e values calculated using chi-square test. \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e\u003cp\u003eCognitive development of toddlers\u003c/p\u003e\u003cp\u003eThe results of cognitive development of toddlers was presented in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Toddlers in the CBF group had significantly higher median composite scores and percentile ranks in both cognitive and language domains compared with those in the DCBF group (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05 for all). No significant group differences were observed in motor development.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eCognitive development of toddlers\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAll\u003c/p\u003e\u003cp\u003e\u003cem\u003e(N\u003c/em\u003e\u0026thinsp;=\u0026thinsp;110)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCBF group\u003c/p\u003e\u003cp\u003e(\u003cem\u003eN\u003c/em\u003e\u0026thinsp;=\u0026thinsp;27)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eDCBF group\u003c/p\u003e\u003cp\u003e\u003cem\u003e(N\u003c/em\u003e\u0026thinsp;=\u0026thinsp;83)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003ep\u003c/em\u003e value\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eComposite Score\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCognitive\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e105 (15)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e110 (10)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e105 (15)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.021 *\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLanguage\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e100 (21)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e106 (15)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e100 (20)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.029 *\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMotor\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e107 (10)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e107 (12)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e103 (13)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.153\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003ePercentile Rank\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCognitive\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e63 (34)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e75 (21)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e63 (38)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.024 *\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLanguage\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e50 (52)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e66 (34)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e50 (52)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.030 *\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMotor\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e68 (25)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e68 (29)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e58 (33)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.139\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eValues are presented as median (interquartile range). CBF group, continued breastfeeding at enrollment; DCBF group, discontinued breastfeeding at enrollment.\u003c/p\u003e\u003cp\u003e\u003cem\u003e*p\u003c/em\u003e values were calculated using the Mann\u0026ndash;Whitney U test. \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e\u003cp\u003eThyroid function of toddlers\u003c/p\u003e\u003cp\u003eBecause thyroid disorders may affect cognitive development in children, two toddlers with abnormally elevated TSH levels were excluded from the analysis. Thus, all participants included in the final dataset had thyroid function values within the normal reference range. As shown in Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, subtle differences in thyroid function were observed between groups. Serum TSH and FT3 levels did not differ significantly; however, FT4 concentrations were significantly higher in the CBF group compared with the DCBF group (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.001). As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, FT4 concentrations were positively correlated with cognitive (r\u0026thinsp;=\u0026thinsp;0.298, p\u0026thinsp;=\u0026thinsp;0.002), language (r\u0026thinsp;=\u0026thinsp;0.290, p\u0026thinsp;=\u0026thinsp;0.002), and motor (r\u0026thinsp;=\u0026thinsp;0.367, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) composite scores, suggesting that higher FT4 levels may contribute to better neurodevelopmental performance in toddlers. In contrast, serum FT3 concentrations showed no significant correlations with cognitive function scores. Although FSH exhibited a negative trend with cognition, the association did not reach statistical significance (data not shown).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eThyroid function of toddlers\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAll\u003c/p\u003e\u003cp\u003e\u003cem\u003e(N\u003c/em\u003e\u0026thinsp;=\u0026thinsp;110)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eCBF group\u003c/p\u003e\u003cp\u003e(\u003cem\u003eN\u003c/em\u003e\u0026thinsp;=\u0026thinsp;27)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eDCBF group\u003c/p\u003e\u003cp\u003e\u003cem\u003e(N\u003c/em\u003e\u0026thinsp;=\u0026thinsp;83)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003ep\u003c/em\u003e value\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTSH (\u0026micro;IU/mL) \u003csup\u003eab\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e3.29\u0026thinsp;\u0026plusmn;\u0026thinsp;1.65\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e3.46\u0026thinsp;\u0026plusmn;\u0026thinsp;1.57\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e3.23\u0026thinsp;\u0026plusmn;\u0026thinsp;1.69\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.534\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFT3 (pg/mL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e4.35\u0026thinsp;\u0026plusmn;\u0026thinsp;0.52\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e4.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.48\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e4.30\u0026thinsp;\u0026plusmn;\u0026thinsp;0.52\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.078\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFT4 (ng/dL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e1.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e1.40\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e1.29\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.001 *\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eValues are expressed as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD. CBF group, continued breastfeeding at enrollment; DCBF group, discontinued breastfeeding at enrollment; TSH, thyroid-stimulating hormone; FT3, free triiodothyronine; FT4, free thyroxine.\u003c/p\u003e\u003cp\u003e*p values were calculated using independent Student\u0026rsquo;s t-test. p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e\u003cp\u003e\u003cem\u003eᵃ\u003c/em\u003e Reference range for TSH in toddlers: approximately 0.7\u0026ndash;5.97 \u0026micro;IU/mL.\u003c/p\u003e\u003cp\u003eᵇ TSH, thyroid-stimulating hormone; FT3, free triiodothyronine; FT4, free thyroxine.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eSince vitamin D, iron status, and thyroid function may influence cognitive function in young children, a multivariable linear regression analyses were further conducted to identify predictors of developmental outcomes. The results demonstrated that higher FT4 levels were significantly associated with better cognitive, language, and motor composite scores on the Bayley-III (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01). In contrast, higher serum 25(OH)D₃ concentrations were negatively associated with cognitive scores (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.013). Sex was an additional predictor of language development, with males exhibiting lower language scores (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.006), while age at assessment showed a borderline positive association with language outcomes (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.054). Other variables, including FT3, hemoglobin, and ferritin, were not significantly associated with developmental domains. (Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eMultiple linear regression predicting cognitive, motor, and language composite scores\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eOutcome\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePredictor\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eB (β)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e95% CI\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003ep-value\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCognition\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFT4 (ng/dL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e22.98 (0.29)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e8.60\u0026ndash;37.35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.002*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFT3 (pg/mL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-3.78 (-0.17)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-7.85\u0026ndash;0.28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.071\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e25(OH)D3 (ng/mL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-0.42 (-0.24)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-0.74\u0026ndash;-0.09\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.013*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHGB (g/dL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.80 (0.07)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-1.33\u0026ndash;2.94\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.463\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFerritin (ng/mL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-0.02 (-0.07)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-0.08\u0026ndash;0.04\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.486\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAge (month)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.07 (0.03)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-0.37\u0026ndash;0.51\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.761\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSex\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-2.19 (-0.10)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-6.33\u0026ndash;1.95\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.302\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLanguage\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFT4 (ng/dL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e26.40 (0.27)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e8.50\u0026ndash;44.31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.005*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFT3 (pg/mL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-3.43 (-0.12)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-8.50\u0026ndash;1.63\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.187\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e25(OH)D3 (ng/mL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-0.11 (-0.05)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-0.51\u0026ndash;0.29\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.593\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHGB (g/dL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-0.96 (-0.06)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-3.62\u0026ndash;1.70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.479\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFerritin (ng/mL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-0.02 (-0.05)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-0.10\u0026ndash;0.06\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.591\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAge (month)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.55 (0.18)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-0.00\u0026ndash;1.10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.054\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSex\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-7.32 (-0.26)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-12.47\u0026ndash;-2.17\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.006*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMotor\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFT4 (ng/dL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e21.85 (0.37)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e10.88\u0026ndash;32.83\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001*\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFT3 (pg/mL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-0.88 (-0.05)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-3.98\u0026ndash;2.22\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.579\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e25(OH)D3 (ng/mL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-0.07 (-0.05)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-0.32\u0026ndash;0.18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.574\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHGB (g/dL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.04 (0.01)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-1.59\u0026ndash;1.68\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.957\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eFerritin (ng/mL)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-0.01 (-0.03)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-0.06\u0026ndash;0.04\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.746\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAge (month)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-0.19 (-0.10)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-0.53\u0026ndash;0.15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.275\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSex\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e-1.72 (-0.10)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e-4.87\u0026ndash;1.44\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.289\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eValues are unstandardized coefficients (B) with standardized β in parentheses. CI\u0026thinsp;=\u0026thinsp;confidence interval. Sex was coded as male\u0026thinsp;=\u0026thinsp;1, female\u0026thinsp;=\u0026thinsp;0. *p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this cross-sectional study of toddlers aged 1\u0026ndash;2 years, we investigated the impact of continued breastfeeding on nutritional status and cognitive development. The main findings were that toddlers in the continued breastfeeding (CBF) group had lower ferritin concentrations and a higher prevalence of iron deficiency compared with those who had discontinued breastfeeding (DCBF). In contrast, vitamin D and iodine status did not differ significantly between groups. Notably, despite the overall normal range of thyroid function, FT4 concentrations were higher in the CBF group, and FT4\u0026mdash;but not FT3\u0026mdash;was positively correlated with cognitive, language, and motor development scores. These results suggest that continued breastfeeding beyond infancy may influence both nutritional biomarkers and neurodevelopmental outcomes in early childhood.\u003c/p\u003e\u003cp\u003eIn our study, toddlers who continued breastfeeding had significantly lower ferritin levels and a higher prevalence of iron deficiency compared with those who had discontinued breastfeeding. This finding is consistent with previous reports suggesting that breast milk alone may not provide sufficient iron beyond six months of age, thereby increasing the risk of iron deficiency and anemia if complementary foods are inadequate[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Iron deficiency has been widely associated with impaired cognitive, behavioral, and psychomotor development, largely due to its critical role in neurotransmitter synthesis and myelination [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. However, when we compared the cognitive outcomes of toddlers with iron deficiency or iron-deficiency anemia to those with normal iron status, no significant differences were observed (data not shown). This may be explained by the fact that our participants did not present with severe anemia, which is often required to manifest measurable impairments in cognitive development. Therefore, while iron deficiency remains an important concern during early childhood, our findings suggest that mild or early-stage deficiency may not exert an immediate or detectable impact on cognitive outcomes.\u003c/p\u003e\u003cp\u003eVitamin D plays an essential role in skeletal growth, calcium homeostasis, and brain development through its involvement in neurotrophic signaling and neuronal differentiation. Previous studies have reported mixed findings regarding the impact of early-life vitamin D status on neurodevelopment. For example, a study in a slum-dwelling infant population found that higher serum 25(OH)D was associated with better temperament, language, and behavioral outcomes, though not with cognitive or motor domains [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Conversely, a longitudinal cohort in North India reported that vitamin D deficiency during early childhood was not linked to cognitive development or linear growth at school age [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. These inconsistent findings underscore the need for further investigation into how vitamin D status influences specific domains of child neurodevelopment. In our cohort, more than 60% of toddlers had either insufficient or deficient vitamin D status, highlighting a common nutritional concern in early childhood. Although we did not find significant differences in vitamin D levels between toddlers who continued breastfeeding and those who had discontinued, the overall prevalence of insufficiency suggests that dietary intake and limited sunlight exposure may contribute to suboptimal vitamin D status in this age group. Previous studies have associated low vitamin D with impaired cognitive and language development, though the evidence remains inconsistent. Thus, vitamin D insufficiency in early life warrants attention, even if its impact on neurodevelopment was not clearly demonstrated in our population.\u003c/p\u003e\u003cp\u003eIodine is a critical component of thyroid hormone synthesis, and its deficiency during early childhood has been linked to irreversible neurodevelopmental impairment [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. In our study, although 22% of toddlers in the CBF group and 30% in the DCBF group had urinary iodine concentrations below 100 \u0026micro;g/L, their thyroid hormone profiles remained within the normal range. Notably, FT4 concentrations were significantly higher in the CBF group compared with the DCBF group, suggesting that continued breastfeeding may exert a modest influence on thyroid function, even in the absence of overt iodine deficiency.\u003c/p\u003e\u003cp\u003eThyroid hormones play a pivotal role in early brain development, particularly in neuronal proliferation, synaptogenesis, and myelination. Among these, free thyroxine (FT4) acts as a critical substrate for local conversion to the biologically active FT3 within neural tissues, emphasizing its importance in neurodevelopment [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. While extensive studies underscore the detrimental impact of clinically low thyroid hormone levels, emerging evidence suggests that even subtle variations in FT4 within the normal range may be biologically meaningful. In our study, FT4\u0026mdash;but not FT3\u0026mdash;demonstrated significant positive correlations with cognitive, language, and motor development in toddlers. This aligns with findings from Meng et al., who conducted a meta-analysis showing that children with neurological disorders exhibited notably lower FT4 levels than healthy controls, although TSH remained unaffected [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Moreover, Taylor's review outlined that early hypothyroidism, often associated with insufficient FT4, can lead to impaired cognitive function [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. Collectively, these findings underscore the notion that FT4 may serve as a more sensitive marker of neurodevelopmental integrity in early childhood compared to other thyroid parameters. Monitoring subtle FT4 fluctuations\u0026mdash;even those within the normative range\u0026mdash;could thus provide valuable insights into the thyroid\u0026ndash;brain developmental axis.\u003c/p\u003e\u003cp\u003eWhile our findings suggest breastfeeding may be associated with subtle elevations in FT4 among toddlers, current literature indicates that human milk contains only minimal levels of thyroid hormones that are unlikely to alter infant thyroid function. According to LactMed, levothyroxine (T4) is present in human milk at trace concentrations (typically\u0026thinsp;\u0026lt;\u0026thinsp;100 \u0026micro;g/L), with limited transfer and negligible clinical effects [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Consistent with earlier findings, Mizuta et al. reported undetectable T4 (including FT4) in breast milk and no significant differences in infant serum thyroid profiles between breastfed and formula-fed groups [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Overall, this suggests that the elevated FT4 observed in our study is more likely attributable to endogenous thyroid activity rather than exogenous hormone ingestion via breast milk.\u003c/p\u003e\u003cp\u003eSeveral cohort studies demonstrate beneficial associations between prolonged breastfeeding and cognitive development. For instance, the Korean MOCEH cohort found that infants breastfed for \u0026ge;\u0026thinsp;9 months scored significantly higher on the Mental Development Index at ages 1 through 3 years, with a clear dose\u0026ndash;response pattern in regression models [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Similarly, children breastfed for more than 3 months exhibited superior communication, problem-solving, expressive language, and vocabulary inference abilities compared to those breastfed for shorter periods [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. More recent evidence reinforces these findings: toddlers breastfed for at least 6 months demonstrated fewer developmental delays in milestone attainment [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e], and prolonged breastfeeding has also been associated with greater cortical thickness, enhanced white-matter myelination, and better executive function into early adolescence [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. Belfort and colleagues emphasized that breastfeeding supports brain development not only through nutrient supply but also through enhanced mother\u0026ndash;infant interaction [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. Consistent with these studies, our findings also showed that continued breastfeeding was associated with better cognitive development in toddlers.\u003c/p\u003e\u003cp\u003eTo our knowledge, this is among the few studies to simultaneously demonstrate the pathway linking breastfeeding with thyroid function and neurodevelopment. Specifically, our findings suggest that prolonged breastfeeding is associated with higher FT4 concentrations, which in turn correlate positively with cognitive performance. This integrated observation provides novel evidence that FT4 may serve as a mediating biomarker between breastfeeding practices and improved cognitive outcomes in toddlers, thereby offering a new perspective on the biological mechanisms underlying the neurodevelopmental benefits of continued breastfeeding. From a clinical and public health perspective, these results highlight the importance of promoting continued breastfeeding while also monitoring thyroid-related biomarkers, as this dual approach may help optimize both nutritional adequacy and neurodevelopmental outcomes in early childhood. Moreover, the potential risk of iron deficiency and iron-deficiency anemia associated with prolonged breastfeeding should not be overlooked. Clinicians are advised to encourage continued breastfeeding while simultaneously monitoring the iron status of toddlers to prevent adverse outcomes. In addition, the high prevalence of vitamin D insufficiency observed in our cohort, regardless of breastfeeding status, represents another important nutritional concern that warrants attention in early childhood.\u003c/p\u003e\u003cp\u003eThis study has several limitations that should be acknowledged. First, its cross-sectional design precludes causal inference regarding the relationships among breastfeeding, nutritional status, thyroid function, and cognitive development. Second, the sample size was relatively small and derived from a single medical center, which may limit the generalizability of the findings to other populations. Third, although no significant differences were observed in maternal and child baseline characteristics, the potential influence of unmeasured confounders\u0026mdash;such as home stimulation, parental intelligence, and genetic factors\u0026mdash;cannot be excluded. Finally, cognitive development was assessed using the Bayley-III at a single time point, which may not fully capture long-term neurodevelopmental trajectories. Future studies employing larger, longitudinal cohorts with repeated developmental assessments are warranted to clarify the causal pathways linking prolonged breastfeeding, micronutrient status, thyroid function, and neurodevelopment. Moreover, mechanistic research is needed to better understand how subtle variations in thyroid hormones, particularly FT4, may mediate the cognitive benefits of breastfeeding.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn summary, this study demonstrated that continued breastfeeding in toddlers was associated with lower ferritin levels and a higher prevalence of iron deficiency, underscoring the importance of timely introduction of iron-rich complementary foods. Vitamin D insufficiency was highly prevalent regardless of breastfeeding status, highlighting another critical nutritional concern in early childhood. Although no significant differences in iodine deficiency were observed between groups, subtle variations in thyroid function were noted, with toddlers who continued breastfeeding exhibiting higher FT4 concentrations. Importantly, FT4 levels were positively correlated with cognitive, language, and motor development, suggesting a potential biological pathway linking breastfeeding with neurodevelopmental outcomes. Taken together, these findings indicate that while prolonged breastfeeding may confer cognitive benefits, careful monitoring of micronutrient status, particularly iron and vitamin D, remains essential to ensure optimal growth and development in toddlers. From a clinical perspective, these results emphasize the need to encourage continued breastfeeding while simultaneously providing appropriate nutritional monitoring and supplementation strategies to maximize both health and developmental outcomes.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eCBF, continued breastfeeding; DCBF, discontinued breastfeeding; CBC, complete blood count; PTH, parathyroid hormone; TSH, thyroid-stimulating hormone; FT3, free triiodothyronine; FT4, free thyroxine; UIC, urinary iodine concentration; Bayley-III, Bayley Scales of Infant and Toddler Development, Third Edition.\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors would like to express their sincere gratitude to all the toddlers and their parents for participating in this study. We also acknowledge the dedicated support of the pediatric staff and clinical psychologist Chia-wen Chang at Shin Kong Wu Ho-Su Memorial Hospital for their invaluable assistance with participant recruitment, sample collection, and cognitive assessments.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was funded by Shin Kong Wu Ho-Su Memorial Hospital (grant number 2019SKHADR021 and 2020SKHADR024).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contribution\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eShu-Chi Mu: Writing \u0026ndash; original draft, Project administration, Investigation, Formal analysis\u003c/p\u003e\n\u003cp\u003eSing-Chung Li:\u0026nbsp;Writing \u0026ndash; original draft, Visualization, Resources, Methodology, Formal analysis\u003c/p\u003e\n\u003cp\u003eYi-Fang Liu: Writing \u0026ndash;review \u0026amp; editing, Urinary iodine analysis\u003c/p\u003e\n\u003cp\u003eYi-Ling Chen: Writing \u0026ndash;review \u0026amp; editing Project administration,\u003c/p\u003e\n\u003cp\u003eLi-Yi Tsai:\u0026nbsp;Writing \u0026ndash;review \u0026amp; editing, Project administration\u003c/p\u003e\n\u003cp\u003eHuei-Ting Kuo:\u0026nbsp;Cognitive development assessment\u003c/p\u003e\n\u003cp\u003eZi-Ying Chen: Project administration, Visualization\u003c/p\u003e\n\u003cp\u003eChiao-Ming Chen: Writing\u0026ndash;review \u0026amp; editing, Writing\u0026ndash;original draft, Visualization, Supervision, Project administration, Methodology, Investigation, Formal analysis, Conceptualization.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study was approved by the Institutional Review Board of Shin-Kong Wu Ho-Su Memorial Hospital (IRB no. 20180901R). The approved study period was from January 2019 to December 2020.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used and analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eVictora CG, Bahl R, Barros AJ, Fran\u0026ccedil;a GV, Horton S, Krasevec J, Murch S, Sankar MJ, Walker N, Rollins NC: \u003cstrong\u003eBreastfeeding in the 21st century: epidemiology, mechanisms, and lifelong effect\u003c/strong\u003e. \u003cem\u003eLancet \u003c/em\u003e2016, \u003cstrong\u003e387\u003c/strong\u003e(10017):475-490.\u003c/li\u003e\n\u003cli\u003eHorta BL, Loret de Mola C, Victora CG: \u003cstrong\u003eLong-term consequences of breastfeeding on cholesterol, obesity, systolic blood pressure and type 2 diabetes: a systematic review and meta-analysis\u003c/strong\u003e. \u003cem\u003eActa Paediatr \u003c/em\u003e2015, \u003cstrong\u003e104\u003c/strong\u003e(467):30-37.\u003c/li\u003e\n\u003cli\u003eChowdhury R, Sinha B, Sankar MJ, Taneja S, Bhandari N, Rollins N, Bahl R, Martines J: \u003cstrong\u003eBreastfeeding and maternal health outcomes: a systematic review and meta-analysis\u003c/strong\u003e. \u003cem\u003eActa Paediatr \u003c/em\u003e2015, \u003cstrong\u003e104\u003c/strong\u003e(467):96-113.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003eWorld Health Organization (WHO). 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Bethesda (MD): National Center for Biotechnology Information (NCBI); 2006.\u003c/li\u003e\n\u003cli\u003eVass RA: \u003cstrong\u003eThyroid hormone and thyroid-stimulating hormone in human milk and infant formula\u003c/strong\u003e. \u003cem\u003eNutrients \u003c/em\u003e2022, \u003cstrong\u003e14\u003c/strong\u003e(8):1688.\u003c/li\u003e\n\u003cli\u003eMizuta H: \u003cstrong\u003eThyroid hormones and thyrotropin in human milk and their influence on neonatal thyroid function\u003c/strong\u003e. \u003cem\u003ePediatric Research \u003c/em\u003e1983, \u003cstrong\u003e17\u003c/strong\u003e:468.\u003c/li\u003e\n\u003cli\u003eLee HJ, et al.: \u003cstrong\u003eThe effect of breastfeeding duration on cognitive development in Korean infants: the MOCEH cohort study\u003c/strong\u003e. \u003cem\u003eBMC Pediatrics \u003c/em\u003e2016, \u003cstrong\u003e16\u003c/strong\u003e:35.\u003c/li\u003e\n\u003cli\u003eKim SY, et al.: \u003cstrong\u003eLonger breastfeeding is associated with improved neurodevelopmental outcomes in early childhood: Evidence from a Korean birth cohort\u003c/strong\u003e. \u003cem\u003eInternational Breastfeeding Journal \u003c/em\u003e2020, \u003cstrong\u003e15\u003c/strong\u003e:51.\u003c/li\u003e\n\u003cli\u003eGoldshtein I, et al.: \u003cstrong\u003eBreastfeeding duration and risk of developmental delay in early childhood\u003c/strong\u003e. \u003cem\u003eJAMA Network Open \u003c/em\u003e2025, \u003cstrong\u003e8\u003c/strong\u003e(1):e2831869.\u003c/li\u003e\n\u003cli\u003eOttino Gonz\u0026aacute;lez J, Fern\u0026aacute;ndez MAR, Esaian S, Rajagopalan V, Bouhrara M, Goran MI, Adise S: \u003cstrong\u003eSustained breastfeeding associations with brain structure and cognition from late childhood to early adolescence\u003c/strong\u003e. \u003cem\u003ePediatr Res \u003c/em\u003e2025.\u003c/li\u003e\n\u003cli\u003eBelfort MB: \u003cstrong\u003eBreastfeeding, brain development, and beyond\u003c/strong\u003e. \u003cem\u003eCurrent Opinion in Pediatrics \u003c/em\u003e2017, \u003cstrong\u003e29\u003c/strong\u003e(2):177-184.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"international-breastfeeding-journal","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ibfj","sideBox":"Learn more about [International Breastfeeding Journal](http://internationalbreastfeedingjournal.biomedcentral.com/)","snPcode":"13006","submissionUrl":"https://submission.nature.com/new-submission/13006/3","title":"International Breastfeeding Journal","twitterHandle":"@BioMedCentral","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-7553779/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7553779/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground :\u003c/h2\u003e\u003cp\u003eTo investigate the associations of continued breastfeeding with micronutrient status, thyroid function, and cognitive development in toddlers.\u003c/p\u003e\u003ch2\u003eMethods:\u003c/h2\u003e\u003cp\u003eIn this cross-sectional study, 110 toddlers aged 1\u0026ndash;2 years were recruited at Shin Kong Wu Ho-Su Memorial Hospital. Participants were categorized into continued breastfeeding (CBF) and discontinued breastfeeding (DCBF) groups. Data collection included anthropometry and Bayley-III cognitive evaluation. Laboratory analyses measured complete blood count, ferritin, 25(OH)D₃, calcium, PTH, TSH, FT3, FT4, and urinary iodine concentration.\u003c/p\u003e\u003ch2\u003eResults:\u003c/h2\u003e\u003cp\u003eToddlers in the CBF group had significantly lower ferritin levels and a higher prevalence of iron deficiency compared with the DCBF group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), while vitamin D insufficiency and suboptimal iodine status were common across both groups. Thyroid hormone profiles of all participants were within normal ranges, but FT4 concentrations were higher in the CBF group (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.001) and were positively associated with cognitive, language, and motor scores on the Bayley-III (all p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Multivariable regression further confirmed FT4 as a significant predictor of developmental outcomes, whereas male sex predicted lower language performance.\u003c/p\u003e\u003ch2\u003eConclusion:\u003c/h2\u003e\u003cp\u003eContinued breastfeeding was associated with improved cognitive outcomes, potentially mediated by higher FT4 concentrations, but also increased risk of iron deficiency. These findings highlight the need to encourage breastfeeding while ensuring appropriate micronutrient monitoring and supplementation, particularly iron and vitamin D, to optimize toddler development.\u003c/p\u003e","manuscriptTitle":"Association of Continued Breastfeeding with Micronutrient Status, Thyroid Function, and Cognitive Development in Toddlers","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-22 09:18:20","doi":"10.21203/rs.3.rs-7553779/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-09-29T19:56:00+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-26T10:44:20+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-21T06:07:32+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"309413142664592340966331712606222832012","date":"2025-09-13T11:05:19+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"65762747013208512141852931564497929053","date":"2025-09-11T03:01:15+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-09-10T20:52:32+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-09-08T10:47:15+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-09-08T10:45:21+00:00","index":"","fulltext":""},{"type":"submitted","content":"International Breastfeeding Journal","date":"2025-09-07T03:22:04+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"international-breastfeeding-journal","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ibfj","sideBox":"Learn more about [International Breastfeeding Journal](http://internationalbreastfeedingjournal.biomedcentral.com/)","snPcode":"13006","submissionUrl":"https://submission.nature.com/new-submission/13006/3","title":"International Breastfeeding Journal","twitterHandle":"@BioMedCentral","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"83ecf2ec-d70d-46cf-84fd-0da6cd4a7680","owner":[],"postedDate":"September 22nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-11T14:24:11+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-22 09:18:20","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7553779","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7553779","identity":"rs-7553779","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}