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Studies on the relationship between iodine, vitamin A (VA), and vitamin D (VD) and thyroid function are limited. This study aimed to analyze iodine and thyroid-stimulating hormone (TSH) status and their possible relationships with VA, VD, and other factors in postpartum women. A total of 1,311 mothers (896 lactating and 415 non-lactating) from Hebei, Zhejiang, and Guangxi provinces were included in this study. The urinary iodine concentration (UIC), TSH, VA, and VD were measured. The median UIC of total and lactating participants were 142.00 µg/L and 139.95 µg/L, respectively. The median TSH, VA, and VD levels in all the participants were 1.89 mIU/L, 0.44 µg/mL, and 24.04 ng/mL, respectively. No differences in the UIC were found between lactating and non-lactating mothers. UIC and TSH levels were significantly different among the three provinces. The rural UIC was higher than the urban UIC. Obese mothers had a higher UIC and a higher prevalence of excessive TSH. Higher UICs and TSHs levels were observed in both the VD deficiency and insufficiency groups than in the VD-sufficient group. After adjustment, no linear correlation was observed between UIC and VA/VD. No interaction was found between vitamins A/D and UIC on TSH levels. The mothers in the present study had no iodine deficiency. Region, area type, BMI, and VD may be related to the iodine status or TSH levels. [ABSTRACT FROM AUTHOR]

Background: Pregnant women, neonates, and school-age children are vulnerable to iodine deficiency. The iodine contents in the environment (drinking water and household salt for cooking) vary by geographical location in China. The aim of this study was to assess the iodine status in vulnerable groups from different geographical zones and analyze the iodine content in household salt and drinking water from these zones.Methods: In coastal and inland regions of Zhejiang Province, China, samples of spot urine, drinking water, and household salt for cooking from both pregnant women and school-age children were determined for iodine concentration between 2017 and 2018. Thyroid-stimulating hormone (TSH) levels from neonates born between 2014 and 2015 were acquired from the Newborns Screening Information System. The iodine status of the vulnerable populations was assessed according to the criteria recommended by the World Health Organization.Results: The median UIC of pregnant women was significantly lower in the coastal region (113.0 μg/L) than the inland region (134.9 μg/L; p < 0.001). The median UICs of pregnant women from these two regions were below the lower optimal iodine cutoff level of 150 μg/L. The percentage of neonates with elevated TSH (> 5 mIU/L) was significantly higher in the coastal region (15.8%) than the inland region (10.5%; p < 0.001). The percentage of neonates with elevated TSH from each region decreased within the range of mild iodine deficiency of 3-19.9%. The median UIC of the coastal school-age children was 156.0 μg/L, and the median UIC of inland children was 181.5 μg/L. Both medians fell within the recommended optimal iodine range of 100-299 μg/L. The iodine concentrations in drinking water varied from 1.0 μg/L in the inland region to 2.0 μg/L in the coastal region. The proportion of households that consumed iodized salt was lower in the coastal region (nearly 65%) than the inland region (approximately 95%).Conclusions: In these two regions with low iodine contents in drinking water, both pregnant women and neonates were iodine-deficient, although school-age children were iodine-sufficient. Urgent efforts are needed to improve the iodine status of pregnant women and neonates. [ABSTRACT FROM AUTHOR]