Iodine and the effects on growth in premature newborns: A focus on the role of thyroid hormones in neurodevelopment and growth

Abstract

Iodine is a trace element which is essential for the synthesis of thyroid hormones. The thyroid hormones thyroxine (T4) and 3,5,3'-triiodothyronine (T3) are necessary for adequate growth and development throughout fetal and extrauterine life. The iodine intake of newborns is entirely dependent on the iodine content of breast milk and the formula preparations used to feed them. An inadequate iodine supply (deficiency and excess) might be especially dangerous in the case of premature babies. The minimum recommended dietary allowance (RDA) is different depending on age groups. The iodine intake required is at least 15 μg/kg per day in full-term infants and 30 μg/kg per day in preterms. Most of the preterm babies are at high risk of iodine deficiency. Neonates and especially preterm infants are a very important population at risk of suffering the consequences of both iodine deficiency and excess, precisely at a stage of growth, psychomotor, and neural development which is extremely sensitive to alterations of thyroid function. If the mother has adequate iodine nutrition, breast milk is the best source of iodine for the newborn. The lactating mother should be supplemented with pharmacological preparations which contain at least 200 μg of iodine. If maternal breastfeeding is not possible, infant formulas containing a high iodine content should be used. Very premature infants should be tested for thyroid function (T4, Free T4, T3, TSH, TBG, and Tg) immediately after birth and repeatedly during their stay in intensive care units, as carefully as they are followed for other organ functions.