Are weaning infants at risk of iodine deficiency even in countries with established iodized salt programs?

Because iodine deficiency (ID) during infancy can irreversibly impair neurodevelopment and increase mortality, it is critical that dietary iodine is adequate in this vulnerable group. Lactating mothers consuming iodized salt can transfer adequate iodine to the infant via breast milk, but during the weaning period, infants are at risk for ID for several reasons: (1) requirements per kg bodyweight for iodine and thyroid hormone during infancy are higher than at any other time in the life cycle; (2) experts recommend no extra salt (iodized or not) be given to infants during the first year; (3) cow's milk (a major source of dietary iodine in many countries) is also not recommended for infants during the first year; and (4) iron deficiency, a common disorder during infancy, can impair iodine metabolism and reduce thyroid hormone production. For many weaning infants in industrialized countries, iodine fortified into commercial infant foods becomes important. This has recently been demonstrated in Switzerland, where a long-standing iodized salt program provides adequate iodine to pregnant women and school-age children, but new national data suggest weaning infants not receiving iodine-containing commercial baby foods have inadequate iodine intakes. Thus, even in countries with effective iodized salt programs, infants may be at risk of ID during weaning and may need additional dietary and/or supplemental sources of iodine.