Context: Iodine deficiency (ID) in utero impairs fetal growth, but the relationship between ID and postnatal growth is less clear.

Objective: To determine if iodine repletion improves somatic growth in iodine-deficient children and to investigate the role of insulin-like growth factor (IGF)-1 and insulin-like growth factor binding protein (IGFBP)-3 in this effect.

Design, participants, and interventions: Three prospective, double blind intervention studies were done: 1) in a 10 month study, severely iodine-deficient, 7-10 y-old Moroccan children (n = 71) were provided iodized salt and compared with children not using iodized salt; 2) in a 6 month study, moderately iodine-deficient, 10-12 y-old Albanian children (n = 310) were given 400 mg iodine as oral iodized oil or placebo; 3) in a 6 month study, mildly iodine-deficient 5-14 y-old South African children (n = 188) were given two doses of 200 mg iodine as oral iodized oil or placebo. At baseline and follow-up, height, weight, urinary iodine (UI), total thyroxine (TT4), thyroid-stimulating hormone (TSH) and IGF-I were measured; in Albania and South Africa, IGFBP-3 was also measured.

Results: In all three studies, iodine treatment increased median UI to >100 µg/L, while median UI in the controls remained unchanged. In South Africa, iodine repletion modestly increased IGF-1, but did not have a significant effect on IGFBP-3, TT4 or growth. In Albania and Morocco, iodine repletion significantly increased TT4, IGF-1, IGFBP-3, weight-for-age z scores and height-for-age z scores.

Conclusion: This is the first controlled study to clearly demonstrate that iodine repletion in school-age children increases IGF-1 and IGFBP-3 concentrations and improves somatic growth.