Discontinuation of salt iodization in children

Department of Human Nutrition
All India Institute of Medical Sciences
New Delhi 110 029
India
E-mail: kapilumesh{at}hotmail.com

Dear Sir:

We read the article entitled "Rapid relapse of thyroid dysfunction and goiter in school-age children after discontinuation of salt iodization" by Zimmermann et al (1) with great interest. One of the major findings of the research investigation was that after 5 mo of discontinuation of the provision of iodized salt to children, the median urinary iodine excretion decreased from 181 to 19 µg/L of urine (from a state of normal iodine nutriture to one of severe iodine deficiency nutriture). This finding raises an important question: how long does it take children with normal iodine nutriture to become severely iodine deficient? If we presume that the intrathyroidal store of iodine is 15 mg (ie, 15 000 µg) (2) and the basic requirement of iodine by the thyroid is 50 µg/d for thyroid function (3), then the intrathyroidal store should be adequate for 300 d. Furthermore, if we presume that the children continued to consume a diet providing 20–30 g I/d (4), which is the usual dietary intake of iodine in a severely iodine-deficient region, the finding of Zimmermann et al that iodine nutriture changed from normal to severe in a span of 5 mo possibly requires another look.

Many studies have documented a reduction in the prevalence of goiter and an increase in the median excretion of iodine to adequate amounts after the introduction of the Universal Salt Iodization Programme (5–11). However, the length of time that it takes for a person with a normal iodine status to become severely iodine deficient needs further investigation.

REFERENCES

1. Zimmermann MB, Wegmüller R, Zeder C, Torresani T, Chaouki N. Rapid relapse of thyroid dysfunction and goiter in school-age children after discontinuation of salt iodization. Am J Clin Nutr 2004;79:642–5.
2. Delange F. Iodine deficiency. In: Braverman LE, Utiger RD, eds. Werner & Ingbar's the thyroid: a fundamental and clinical text. 8th ed. Philadelphia: Lippincott Williams & Wilkins, 2000:295–316.
3. Dunn JT. Iodine deficiency and its elimination by iodine supplementation. In: Braverman LE, ed. Diseases of thyroid. 2nd ed. Atlantic Highlands, NJ: Humanities Press, 2003:329–47.
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10. Kusic Z, Lechpammer S, Lukinac L, Petrovic I, Nothig-Hus D. First beneficial results of the implementation of Croatian new law on salt iodination. J Endocrinol Invest 1999;22(10):747–51.
11. Kapil U, Sohal KS, Shama TD, Tandon M, Pathak K. Assessment of iodine deficiency disorders using the 30 cluster approach in District Kangra, Himachal Pradesh, India. J Trop Pediatr 2000;46:264–6.