Low serum iodine is associated with iodine deficiency and thyroid dysfunctions: a cross-sectional study

Background: The relationship between low serum iodine and thyroid dysfunctions in adults is not well understood. This study aimed to explore the relationship between serum and urinary iodine and thyroid dysfunctions in the adult population. Methods: A total of 1320 participants were included in the final analysis. We collected basic demographic information, as well as blood and spot urine samples, to determine serological indices and iodine nutritional status of subjects. Results: The median (IQR) serum iodine (SI) level was 70.5µg/L (59.6–83.6µg/L). Compared to those with 59.6µg/L ≤ SI < 83.6µg/L, subjects with SI ≤ 59.6µg/L had a higher risk of thyroid dysfunctions (OR = 1.72, 95%CI: 1.08–2.75), clinical hypothyroidism (OR = 16.4, 95%CI: 3.72–72.2) and sUIC < 100µg/L (OR = 1.41, 95%CI: 1.05–2.00). The areas under the ROC curve of SI (0.554, P  = 0.02) was significantly higher than that of sUIC/UCr (0.446, P  = 0.005). Conclusions: Serum iodine is more sensitive than urine iodine in the diagnosis of thyroid dysfunctions. Low serum iodine concentration is associated with an increased risk of thyroid dysfunctions, especially hypothyroidism.