Interrelationships Among Vitamin D Status and Body Composition in Mother-Infant Dyads

Background: Vitamin D status of pregnant women is associated with body composition of the offspring. The objective of this study was to assess whether the association between maternal vitamin D status and neonatal adiposity is modified by maternal adiposity preconception. Methods: Healthy mothers and their term appropriate weight for gestational age (AGA) infants (n=142; 59% male, Greater Montreal, March 2016-2019) were studied at birth and 1 month postpartum (2-6 weeks). Newborn (24-36 hour) serum was collected to measure total 25-hydroxyvitamin D [25(OH)D] (immunoassay); maternal pre-pregnancy BMI was obtained from the medical record. Anthropometry, body composition (dual-energy X-ray absorptiometry) and serum 25(OH)D were measured at 2-6 weeks postpartum in mothers and infants. Mothers were grouped into 4 categories based on their vitamin D status (sufficient 25(OH)D ≥50 nmol/L vs. at risk of being insufficient <50 nmol/L) and pre-pregnancy BMI (<25 vs. ≥25 kg/m 2 ): insufficient-recommended weight (I-RW, n=24); insufficient-overweight/obese (I-OW/O, n=21); sufficient-recommended weight (S-RW, n=69); and sufficient-overweight/obese (S-OW/O, n=28). Partial correlation and mixed model ANOVA were used while adjusting for covariates. Results: : At birth, infant serum 25(OH)D mean concentrations were below the cut-point for sufficiency of 50 nmol/L for both maternal pre-pregnancy BMI categories; 47.8 [95%CI: 43.8, 51.9] nmol/L if BMI <25 kg/m 2 and 38.1 [95%CI: 33.5, 42.7] nmol/L if BMI ≥25 kg/m 2 . Infant serum 25(OH)D concentrations at birth (r=0.77; p<0.0001) and 1 month (r=0.59, p<0.0001) were positively correlated with maternal postpartum serum 25(OH)D concentrations. Maternal serum 25(OH)D concentration was inversely associated with maternal percent whole body fat mass (r=-0.26, p=0.002). Infants of mothers in I-OW/O had higher fat mass versus those of mothers in S-OW/O (914.0 [95%CI: 766.4, 1061.6] vs. 780.7 [95%CI: 659.3, 902.0] g; effect size [Hedges' g 0.42]; p=0.04) with magnitude of difference of 220.4 g or ~28% difference (adjusting for covariates). Conclusions: : Maternal vitamin D status is positively correlated with neonatal vitamin D. In this study, maternal adiposity and serum 25(OH)D <50 nmol/L are dual exposures for neonatal adiposity. These findings reinforce the importance of vitamin D supplementation early in infancy irrespective of vitamin D stores acquired in utero and maternal weight status .