High thyroid volume in children with excess dietary iodine intakes

Department of Human Nutrition
All India Institute of Medical Sciences
New Delhi 110029
India
E-mail: drrajat_prakash{at}yahoo.co.in

Dear Sir:

The recent article titled "High thyroid volume in children with excess dietary iodine intakes" by Zimmermann et al (1) made interesting reading. The authors highlighted one of the possible risks (2) associated with excess dietary intake of iodine. The eventuality of adverse effects due to dietary excess of iodine is plausible in the current scenario of universal salt iodization, particularly so when monitoring is poor (3).

The main finding of the close correlation between increase in thyroid volume and high iodine intake in children documented by Zimmerman et al is based mainly on data from coastal Hokkaido. This association is not entirely new; endemic goiter due to dietary excess of iodine was recognized decades ago in coastal Hokkaido (4, 5). However, despite the excessively high intake of iodine universally in coastal Hokkaido, the prevalence of goiter has never been documented to be >25% (6). Other factors may play a role in the etiology of goiter in this region, and the drawing of conclusions based on data from this region may not be appropriate. In the same context, it would be of interest to know the goiter prevalence rates in the subsample from coastal Hokkaido in study by Zimmerman et al.

Whatever may be the deliberations to the issues raised above, it is hoped that the interest and research generated by this study are directed toward strengthening the monitoring system of salt iodization programs rather than creating doubts in the minds of health policy makers and thereby derailing successful programs such as universal salt iodization, particularly in developing countries.

REFERENCES

1. Zimmermann MB, Ito Y, Hess SY, Fujieda K, Molinari L. High thyroid volume in children with excess dietary iodine intakes. Am J Clin Nutr 2005;81:840–4.
2. Pennington JAT. Iodine toxicity. Springfield, VA: National Technical Information Service, US Department of Commerce, 1989.
3. Delange F, de Benoist B, Pretell E, Dunn JT. Iodine deficiency in the world: where do we stand at the turn of the century? Thyroid 2001;11:437–47.
4. Suzuki H, Higuchi T, Sawa K, Ohtaki S, Horiuchi Y. "Endemic coast goiter" in Hokkaido, Japan. Acta Endocrinol (Copenh) 1965;50:161–76.
5. Wolff J. Iodine goiter and the pharmacological effects of excess iodide. Am J Med 1969;47:101–24.
6. Suzuki H. Etiology of endemic goiter and iodide excess. In: Stanbury JB, Hetzel BS, eds. Endemic goiter and endemic cretinism. Iodine nutrition in health and disease. New Delhi, India: Wiley Eastern Limited, 1985;237–53.