The effects of mild iodine deficiency on neonatal thyroid function

In order to assess neonatal thyroid function in the endemic goitre areas of Greece, T4 and TSH have been measured. Previous studies had shown that in these endemic areas, adults had low T4 but normal TSH values, probably because of an increase in the serum T3 level. In this study, T4 and TSH were measured in dried blood spots from 259 neonates. The fifty-four full-term neonates from the Greek endemic villages had a lower T4 value (8.8 +/- 0.66 micrograms/dl SE) but a higher TSH (15.37 +/- 1.12 mu/l) than the seventy-three full-term neonates from the non-endemic villages (T4:10.0 +/- 0.33 micrograms/dl, TSH:11.93 +/- 0.59 mu/l) or the ninety-eight from Athens (T4:10.0 +/- 0.33 micrograms/dl, TSH:10.96 +/- 0.64 mu/l). Premature neonates, both from Athens and from the endemic areas, have significantly lower T4 and significantly lower TSH values than the full-term ones from the same areas, probably because of the immaturity of the pituitary-thyroidal axis. It is concluded from these observations that (a) Neonates suffer more from the consequences of iodine deficiency than adults. The biochemical hypothyroidism reported here may be relevant to the delayed skeletal maturation previously reported from children of these same areas. This emphasizes the need for correcting even moderate iodine deficiency. (b) The occurrence of non-toxic goitre with normal TSH levels in adults is best explained by assuming that increased TSH stimulation is necessary for goitre formation during neonatal life, but not for goitre maintainance during adulthood. (c) Newborn screening programmes in these areas should take into account the present findings.