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Treatment of Iodine Deficiency in School-Age Children Increases Insulin-Like Growth Factor (IGF)-I and IGF Binding Protein-3 Concentrations and Improves Somatic Growth

Laboratory for Human Nutrition (M.B.Z., R.B.), Swiss Federal Institute of Technology, CH-8092 Zürich, Switzerland; Medical Research Council (P.L.J., S.S.), Cape Town 7505, South Africa; University of Venda (N.S.M., X.M.), Thohoyandou 0950, South Africa; The Ministry of Health (N.C.), Rabat, Morocco; The Ministry of Health (M.B.), Tirana, Albania; University Hospital (L.G.), 372 Tirana, Albania; and Child Advocacy International (J.B.), Newcastle under Lyme ST5 1ND, United Kingdom

Address all correspondence and requests for reprints to: Michael B. Zimmermann, M.D., Laboratory for Human Nutrition, Swiss Federal Institute of Technology, LFV E19, Schmelzbergstrasse 7, CH-8092 Zürich, Switzerland. E-mail: michael.zimmermann{at}ilw.agrl.ethz.ch.

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

Objective: The objective of the study was to determine whether iodine repletion improves somatic growth in iodine-deficient children and investigate the role of IGF-I and IGF 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- to 10-yr-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- to 12-yr-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- to 14-yr-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 T₄ (TT4), 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 more than 100 µg/liter, whereas median UI in the controls remained unchanged. In South Africa, iodine repletion modestly increased IGF-I but did not have a significant effect on IGFBP-3, TT4, or growth. In Albania and Morocco, iodine repletion significantly increased TT4, IGF-I, 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-I and IGFBP-3 concentrations and improves somatic growth.

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