Perspective from Elizabeth N. Pearce, MD, MSc
November 27, 2013
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Breast-feeding may provide infants with adequate iodine supplementation

Perspective from Elizabeth N. Pearce, MD, MSc
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Iodine supplementation allowed lactating women to provide their infants with adequate iodine via breast milk for at least 6 months, according to recent study data published in The Lancet.

This route of delivery appeared to be safe and rapidly normalized thyroid function for the infants included in the study, according to Raschida Bouhouch, MSc, a PhD student in the laboratory of human nutrition at ETH Zurich, and colleagues.

They assessed the maternal and infant urinary iodine, breast milk iodine, maternal and infant thyroid-stimulating hormone, maternal and infant free thyroxine, and the infant growth of 241 mother-infant pairs.

Pairs were assigned to indirect infant supplementation in which mothers received iodine 400 mg as iodized oil and infants received placebo (n=121) or direct infant supplementation in which infants received iodine 100 mg as iodized oil and mothers received placebo (n=118).

Median urinary iodine concentration levels of 35 mcg/L in mothers and 73 mcg/L in infants signaled iodine deficiencies at baseline. Measurements of maternal urinary iodine (P=.011), breast milk iodine (P<.0001) and infant urinary iodine concentrations (P=.042) were higher in the indirect infant supplementation group vs. the direct supplementation group.

Maternal TSH (P=.276) and T4 (P=.074) concentrations and infant TSH (P=.597) and T4 (P=.184) did not vary between groups throughout the study. However, researchers report that the number of infants with thyroid hypofunction was lower (P=.023) in the indirect supplementation group compared with the direct supplementation group.

Median infant urinary iodine concentrations in the indirect infant supplementation group was adequate (>100 mcg/L) at 3 and 6 months, according to researchers. However, infant urinary iodine concentrations demonstrated that levels were only sufficient at 6 months among those in the direct supplementation group.
In an accompanying commentary, Sarah C. Bath, PhD, RD, a postdoctoral research fellow at the University of Surrey in the United Kingdom, wrote that a deficiency of iodine during the early stages of life can result in impaired child cognition and has been associated with infant mortality.

“Iodine is needed for thyroid hormone production and iodine sufficiency is particularly important during pregnancy, lactation, and infancy owing to the role of thyroid hormones in brain development,” Bath wrote.

WHO recommends that lactating mothers ingest a daily dose of 250 mcg as potassium iodide or one annual depot dose of 400 mg as oral iodized oil, and exclusive breast-feeding for at least the first 6 months of life. In a press release, Bouhouch said WHO recommendations may be inadequate and require adjustments.

For more information:

Bath SC. Lancet. 2013;doi:10.1016/S2213-8587(13)70185-2.

Bouhouch RR. Lancet. 2013;doi:10.1016/S2213-8587(13)70155-4.

Disclosure: The researchers report no relevant financial disclosures.