Iodine in breast milk: a systematic review

Authors: DROR, DAPHNA - Consultant; Allen, Lindsay - A

Submitted to: Advances in Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2017
Publication Date: 5/29/2018
Citation: Dror, D., Allen, L.H. 2018. Iodine in breast milk: a systematic review. Advances in Nutrition. 9:347S-357S. https://doi.org/10.1093/advances/nmy020.
DOI: https://doi.org/10.1093/advances/nmy020

Interpretive Summary: Because infants are born with small stores of iodine in their thyroid gland they depend on breast milk iodine for normal physical and neurological growth and development. The mammary gland concentrates iodide, however there is a lack of agreement on the concentration of breast milk iodine necessary to achieve adequate iodine status in the infant. The objectives of this review are to consider trends in breast milk iodine concentration during lactation, to determine which maternal factors or interventions influence breast milk iodine, to examine the association between breast milk iodine concentration and infant iodine status, and to identify how recent data contribute to the literature and inform recommendations for achieving optimal breast milk iodine levels. Milk iodine concentration varies widely between populations but is highest in colostrum and decreases gradually throughout lactation. The studies we considered did not support earlier findings of an inverse correlation between breast milk iodine concentration and perchlorate. Supplementation with high dose or daily iodine during lactation is effective for increasing breast milk iodine with some evidence of a dose-response relationship, consistent with findings of earlier supplementation trials in pregnancy and lactation. Though additional research is needed, data suggest that breast milk iodine concentration around 150 µg/L during the first 6 months of lactation would achieve or exceed infant iodine needs and prevent the developmental consequences of iodine deficiency.

Technical Abstract: Because infants are born with small amounts of stored intrathyroidal iodine, they depend on breast milk iodine for normal physical and neurological growth and development. The mammary gland concentrates iodide, however there is a lack of consensus on the concentration of breast milk iodine necessary to achieve equilibrium in the infant. The objectives of the present review are to consider trends in breast milk iodine concentration over the course of lactation, to determine which maternal factors or interventions influence breast milk iodine concentration, to examine the association between breast milk iodine concentration and infant iodine status, and to identify how recent data contribute to the literature and inform recommendations for achieving optimal breast milk iodine concentration. A systematic search of published literature was undertaken using the US National Library of Medicine’s MEDLINE/PubMed bibliographic search engine. Observational and intervention studies were included if research was original, the study had not been included in a prior review, and iodine concentration in human milk was 39 measured at one or more time points during the first twelve months of lactation. Results of the systematic review indicate that breast milk iodine concentration varies widely between populations but is highest in colostrum and decreases gradually throughout the lactation period. Included studies did not replicate earlier findings of an inverse correlation between breast milk iodine concentration and perchlorate. Supplementation with high dose or daily iodine during lactation was effective for increasing breast milk iodine concentration with some evidence of a dose-response relationship, consistent with findings of earlier supplementation trials in pregnancy and lactation. Though additional and globally representative research is needed, data suggest that breast milk iodine concentration in the range of 150 µg/L during the first 6 months of lactation would achieve or exceed infant iodine equilibrium and prevent the developmental consequences of iodine deficiency.