Breast Milk Iodine Concentration Rather than Maternal Urinary Iodine Is a Reliable Indicator for Monitoring Iodine Status of Breastfed Neonates.

Abstract

There is no scientific consensus on whether breast milk iodine concentration (BMIC) accurately reflects iodine status in lactating mothers and breastfed infants. This study aimed to compare BMIC and maternal urinary iodine concentration (UIC) as indicators of iodine status in breastfed neonates. In this cross-sectional study, 147 lactating mothers and their neonates (3-5days postpartum) were randomly selected from health care centers. Breast milk and urine samples were collected from each mother and neonate, and a heel-prick blood sample was taken from all neonates as part of a congenital hypothyroidism screening program. According to the World Health Organization criteria, median urinary iodine concentration (UIC) ≥ 100μg/L in lactating mothers and neonates indicates iodine sufficiency. In areas of iodine sufficiency, median BMIC ≥ 100μg/L is considered an adequate level. Overall, 129 (89.0%) and 16 (11.0%) mothers had BMICs ≥ 100 and ˂100μg/L, respectively. Median (interquartile range [IQR]) maternal UIC was 70μg/L (42-144μg/L) and 37μg/L (25-100μg/L) in mothers with breast milk iodine levels ≥ 100 and ˂100μg/L, respectively (P = 0.047); values for UIC of neonates born to mothers with BMICs ≥ 100 and ˂100μg/L were 230μg/L (114-310μg/L) and 76μg/L (41-140μg/L), respectively (P < 0.001). In the linear regression model, neonate UIC was positively associated with BMIC in both unadjusted (β = 0.558, P < 0.001) and adjusted analysis (β = 0.541, P < 0.001). A similar result was found in logistic regression analysis, indicating that neonates born to mothers with BMIC ≥ 100μg/L were more likely to have UIC ≥ 100μg/L compared to those whose mothers had BMIC < 100μg/L in both unadjusted (OR = 7.93, P < 0.001) and adjusted analysis (OR = 7.29, P = 0.001). The present findings indicate that BMIC is a more sensitive indicator than maternal UIC for assessment of iodine status in breastfed neonates. To address low levels of maternal UIC, further studies on the prescription of supplements containing 150μg/day iodine during lactation period are warranted.