Assessment of iodine status of lactating women and infants in Shanghai, China

There is a risk of iodine deficiency in pregnant women in China. However, currently, little research is available on the iodine status of lactating women and infants. This study aimed to evaluate the iodine status of lactating women and their infants and explore the relationship between breast milk iodine concentration (BMIC) and urinary iodine concentration (UIC). 257 lactating women and their infants were recruited from the Shanghai Sixth People’s Hospital East campus between May 2018 and May 2019. BMIC and UIC were measured by inductively coupled plasma mass spectrometry (ICP-MS). One-day 24-hour dietary recall was used to determine the dietary intake of iodine. The mean dietary intake of iodine of the lactating women was 145.1 µg/day. The dietary iodine intake of 97.83% (n=225) of lactating women was lower than 240 µg/day. The median BMIC and UIC of the lactating women and UIC of the infants were 150.7 µg/L (Interquartile Range, IQR 102.9, 205.5), 110.0 µg/L (IQR 65.8, 171.4) and 212.7 µg/L (IQR 142.1, 320.6), respectively. The BMIC of lactating women who ate iodized salt was significantly higher than that without 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. The use of iodized salt was related to increasing dietary iodine intake and BMIC. The improvement of BMIC has a positive effect on the iodine nutrition level of infants. Compared with the level of urinary iodine of mothers, BMIC was a more sensitive and stable index to evaluate the iodine nutritional status of infants.