Keep an Eye on Iodine and the Thyroid and Save the Brain

iodine content of the mother’s diet. Iodine readily passes the placenta [5] , and the mother’s dietary iodine intake should cover the needs of both the maternal and the fetal thyroid hormone production. Compared with the nonpregnant state, the thyroid hormone production is up to 50% higher from early pregnancy due to a high degradation rate of T 4 in the placenta/uterus unit and various other mechanisms [3] . Thus, iodine requirements are substantially increased in pregnancy [1] . During breastfeeding, around 40% of iodine in the mother’s diet are transferred to the infant via breast milk [6, 7] , and the mother’s iodine intake should be relatively high to cover both her own needs and the iodine transfer via breast milk [1] . Smoking and other sources of thiocyanate diminish iodine transport into breast milk [8] , and mothers who smoke or who are exposed to other inhibitors of the mammary gland iodine transport should have an even higher iodine intake. A few months’ delay in the diagnosis and therapy of congenital hypothyroidsm involves a high risk of some degree of permanent intellectual impairment of the child. As a consequence, a neonatal screening program for hypothyroidism was initiated in Turkey in 2006 [2] . Moreover, considerable parts of the Turkish population had previously been affected by iodine insufficiency, and a program of salt iodisation was introduced in the late 1990s [9] . Even if salt iodisation has in general increased iodine intake in the Turkish population [9] , areas of low iodine Thyroid hormones are indispensable developmental factors and a lack of adequate amounts of thyroid hormone during brain development may lead to irreversible brain damage [1] . Thus, it is vital that neonates diagnosed with hypothyroidism are treated fast and adequately to become euthyroid. In this issue of Hormone Research in Paediatrics , Kurtoglu and colleagues from Kayseri, Turkey, report an interesting study where an iodine supplement was added to the obligatory levothyroxine replacement therapy of neonates diagnosed by screening to suffer from hypothyroidism [2] . A lack of thyroid hormone for proper brain development may have several main causes: (1) maternal thyroid insufficiency, because the thyroid hormones involved in steering the development in early pregnancy are entirely of maternal origin, and those involved in late pregnancy are partly of maternal (and partly of fetal) origin. The typical cause is autoimmune impairment of the thyroid in the mother, and it is much discussed if all pregnant women should be screened in early pregnancy for thyroid dysfunction [3] . (2) Fetal/neonatal/infant thyroid insufficiency is most often caused by developmental defects such as thyroid aplasia/hypoplasia/ectopia or abnormalities in processes involved in thyroid hormone production [4] . Screening for neonatal hypothyroidism is now part of public healthcare in many countries, but still only a minority of the world’s newborns are screened [4] . (3) Insufficient thyroid hormone production in both the mother and the fetus/infant is typically caused by an insufficient Published online: May 15, 2014 HORMONE RESEARCH IN PAEDIATRICS