Don't forget iodine after pregnancy

The Paper of the Month for June is from the British Journal of Nutrition and is entitled ‘Infant iodine status and associations with maternal iodine nutrition, breastfeeding status and thyroid function' by Synnøve Næss, Inger Aakre, Tor A. Strand, Lisbeth Dahl, Marian Kjellevold, Ann-Elin Meling Stokland, Bjørn Gunnar Nedrebø and Maria Wik Markhus.

Iodine is an essential micronutrient for humans throughout life due to its need for the production of the thyroid hormones. The nutrient is particularly important during pregnancy and in the first year of life, as the thyroid hormones are essential for growth and normal development of the brain and nervous system of the foetus and young children. Currently, iodine deficiency is one of the most common nutritional disorders globally. Furthermore, the World Health Organization has declared iodine deficiency as the single most important cause of preventable brain damage in foetuses and infants.

During the last decade, countries in Europe have reported iodine deficiency among several population groups, including pregnant and lactating women. But what about iodine status among the smallest children? To date, few studies have measured iodine status in infants during the first year of life.

In this study, we measured iodine status among infants in Norway at ages 3, 6 and 11 months. We found that the infants had insufficient iodine status at age 3 months. However, iodine status increased during the first year of life and was adequate at both ages 6 and 11 months. In the first months of life, breastfed infants were at highest risk of iodine deficiency. This finding can most likely be explained by maternal iodine status, as the mothers also were defined as iodine deficient. We found that maternal iodine status and the iodine concentration in breast milk were associated with infant iodine status; hence, the higher maternal iodine status, the higher infant iodine status. Compared with fully breastfed infants, weaned and formula-fed infants were less vulnerable to iodine deficiency. This may be because of iodine provided through complementary foods and formula. Although infants aged 3 months had inadequate iodine status in this study, there was a low prevalence of thyroid dysfunction. Furthermore, because we found no associations between infant iodine status and thyroid function, we do not know the clinical impact of the observed iodine deficiency among the fully breastfed infants.

The findings of this study demonstrate that breastfed infants are at risk of iodine deficiency in the first months of life as a consequence of maternal iodine deficiency. Awareness of promoting adequate iodine nutrition for lactating women should be prioritised to secure sufficient iodine intake for mothers and, subsequently, their infants.