Comparison of breast-milk iodine concentration of lactating women in Australia pre and post mandatory iodine fortification

Objective: To compare the breast-milk iodine concentrations (BMIC) of lactating women before and after the mandatory iodine fortification of bread in Australia in 2009.

Design: Cross-sectional study. Breast milk samples were collected from two cohorts of women in South Australia within 7 d of delivery to determine BMIC. The percentage of samples with iodine concentration below 100 μg/l, a level considered adequate for breast-fed infants, was calculated. Sociodemographic information and intake of dietary supplements were obtained from all women.

Setting: The breast milk samples were collected between 2006 and 2007 in the pre-fortification cohort and between 2012 and 2013 in the post fortification cohort.

Results: The median (interquartile range) BMIC was higher in the post-fortification samples compared with samples collected in the pre-fortification period (187 (130–276) v. 103 (73–156) μg/l; P<0·05). Overall, the percentage of women with BMIC <100 μg/l was lower in the post-fortification cohort than in the pre-fortification cohort (13 v. 49 %; P<0·01). The percentage of women with BMIC <100 μg/l in the post-fortification cohort was lower among women who took iodine supplements in pregnancy (12 v. 29%; P <0·01).

Conclusions: Mandatory iodine fortification of bread has resulted in an increase in the iodine content of breast milk in Australian women. However, iodine supplementation may still be required in some women post-iodine fortification to reach the level of BMIC that is considered adequate to meet the iodine requirement of full-term infants.