Clinical Thyroidology® for the Public

Summaries for the Public from recent articles in Clinical Thyroidology
Table of Contents | PDF File for Saving and Printing

Mothers taking iodine supplementation while breastfeeding may improve child’s brain development at 3 years of age

Clinical Thyroidology for the Public

Instagram Youtube LinkedIn Facebook Twitter

Iodine is an essential element used to make thyroid hormone, which is especially important for baby’s normal brain development during pregnancy. Iodine deficiency is an important cause of hypothyroidism world-wide. Iodine is taken up into breastmilk in breastfeeding mothers to provide iodine for babies. Because brain development continues in early childhood after birth, breastfeeding mothers should have enough iodine intake to provide adequate iodine for their babies. Currently, many societies, including the American Thyroid Association, recommend that women who are planning to be pregnant, are pregnant, or are breastfeeding should take a supplement that contains 150 μg of iodine every day. Severe iodine deficiency in pregnancy and early childhood is well known to have negative effects on child’s brain development. However, effects of mild-to-moderate iodine deficiency in breastfeeding mothers are less clear. This study studied long-term effects of iodine supplements given to breastfeeding mothers on child’s development at 3 years of age.

Nazeri P et al 2021 Dose maternal iodine supplementation during the lactation have a positive impact on the neurodevelopment of children? Three-year follow up of a randomized controlled trial. Eur J Nutr. Epub 2021 May 11. PMID: 33974129.

A total of 180 breastfeeding mothers without thyroid disease and their full-term babies at 3 to 5 days of age were initially recruited from health care centers in Iran between October 2014 and January 2016. Mothers were randomly assigned to three groups according to types of supplements that were given for 12 months – placebo (no iodine), 150 μg/day of iodine, and 300 μg/day of iodine. Among these mother-child pairs, 122 children (42 children in placebo group, 35 children in 150 μg/day iodine group, and 45 children in 300 μg/day iodine group) had developmental testing at 3 years of age.

Iodine status at population level can be evaluated by measuring an average urinary iodine concentration (UIC) of many people, although this is not a good measure for an individual person. An average UIC ≥ 100 μg/L means that the studied population has adequate iodine nutrition as a group. Mothers in this study had mild-to-moderate iodine deficiency because their average UIC was < 100 μg/L. However, their infants in all groups all had adequate iodine with their average UIC > 100 μg/L. The average scores for brain, language, and motor development were similar among all the treatment groups. There was no significant difference in number of children with neurodevelopmental delays among the treatment groups. However, brain scores were higher in children of mothers who received 150 μg/day iodine supplementation than children whose mothers received placebo, when other factors that may affect child’s test scores were taken into account. There were no significant differences in brain scores between children in 300 μg/day iodine group and placebo group, or between children in 300 μg/day iodine group and 150 μg/day iodine group. There were no significant differences in language or motor scores across the treatment groups.

This study suggests that supplementing breastfeeding mothers who have mild-to-moderate iodine deficiency with 150 μg/day of iodine may benefit children’s brain development. It would be important for breastfeeding mothers to have adequate iodine nutrition if their infants were exclusively breastfed. However, adequate iodine nutrition for infants, regardless of the source of iodine, may be able to overcome effects of iodine deficiency in the mother during the childs early life, and iodine may be supplemented via formula to babies if needed. Larger trials would be needed to further assess the benefits of iodine supplementation in breastfeeding mothers.

— Sun Y. Lee, MD


Iodine: an element found naturally in various foods that is important for making thyroid hormones and for normal thyroid function. Common foods high in iodine include iodized salt, dairy products, seafood and some breads.

Hypothyroidism: a condition where the thyroid gland is underactive and doesn’t produce enough thyroid hormone. Treatment requires taking thyroid hormone pills.