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Endocrine-disrupting chemicals necessitate emphasis on iodine nutrition in breast-feeding mothers

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November 16, 2017

Sun Lee
Sun Y. Lee

Although breast-feeding women in the U.S. overall met WHO-recommended iodine levels for lactating women, environmental perchlorate and thiocyanate exposure may counteract iodine nutrition, according to researchers.

“This study provides further understanding of the state of iodine nutrition in U.S.-lactating women,” Sun Y. Lee, MD, of the section of endocrinology, diabetes and nutrition at Boston University School of Medicine, told Endocrine Today. “Breast-feeding women should ensure that they have adequate iodine intake in order to provide adequate iodine nutrition to their breast-fed infant, given the ubiquitous exposure to low-level perchlorate and thiocyanate. In fact, the American Thyroid Association recommends that breast-feeding women take a supplement containing 150 µg/L of iodine per daily dose to ensure adequate iodine nutrition.”

Lee and colleagues evaluated data on 376 women (mean age, 31.1 years; 37% white) who were lactating from three U.S. geographic regions (California, Massachusetts and Ohio/Illinois) between November 2008 and June 2016 to assess iodine sufficiency and whether iodine level is associated with low-level environmental perchlorate and thiocyanate exposures.

WHO currently recommends urinary iodine concentration of at least 100 µg/L in lactating women, and overall median concentrations were 143 µg/L for all participants. No differences were observed between the regions for levels of median urinary iodine, perchlorate levels, thiocyanate levels or proportion of women with median urinary iodine concentrations less than 100 µg/L.

Positive correlations were observed between spot urinary iodine, perchlorate and thiocyanate levels.

Perchlorate and iodine levels and thiocyanate and iodine levels were significantly correlated in participants with median urinary iodine concentrations less than 100 µg/L.

“Although we demonstrate that lactating women in our study ... were overall iodine sufficient, approximately one-third had low urinary iodine levels to potentially be of concern,” Lee said. “Since iodine is needed for thyroid hormone production, which is, in turn, important for ongoing brain development even in the postnatal period, adequate iodine nutrition should be emphasized among breast-feeding women in order to provide optimal iodine nutrition for their breast-fed infant.

“Also, we demonstrated that there is universal low-level exposure to environmental perchlorate and thiocyanate, two common endocrine-disrupting chemicals that interfere with iodine uptake into the thyroid gland and lactating breast, among our cohort study,” Lee said. – by Amber Cox

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Sun Y. Lee, MD, can be reached at

Disclosures: The authors report no relevant financial disclosures.