Assessment of the Iodine Status of Lactating Women and Infants in Shanghai, China

There is a risk of iodine deficiency among pregnant women in China. However, research on the iodine status of lactating women and infants is scarce. In this study, we aimed to evaluate the iodine status of lactating women and their infants and explore the relationship between breast milk iodine concentrations (BMICs) and urinary iodine concentrations (UICs). In total, 257 lactating women and their infants were recruited from the Shanghai Sixth People's Hospital East campus between May 2018 and May 2019. The BMIC and UIC were measured by inductively coupled plasma-mass spectrometry (ICP-MS). One-day 24-h dietary recall was used to determine the dietary intake of iodine. The mean dietary intake of iodine among the lactating women was 145.1 mu g/day, and 97.83% (n = 225) of the lactating women had a dietary iodine intake below 240 mu g/day. The median BMIC and UIC of the lactating women was 150.7 mu g/L (interquartile range, IQR 102.9, 205.5) and 110.0 mu g/L (IQR 65.8, 171.4), respectively, and the median UIC of the infants was 212.7 mu g/L (IQR 142.1, 320.6). The BMIC of lactating women who consumed iodized salt was significantly higher than that of lactating women who did not consume iodized salt (p = 0.015). The infants' UIC values were significantly correlated with the BMIC values (r = 0.597*, p < 0.001). The iodine nutritional status of lactating women and infants in Shanghai was generally sufficient according to the WHO's iodine nutritional status recommendation. The use of iodized salt was related to increasing dietary iodine intake and the BMIC. Improvements in BMICs have positive effects on the nutritional levels of iodine in infants.