Nutrition News for Africa

Abstract - October 15, 2007

An article entitled “Vitamin A supplementation in iodine-deficient African children decreases thyrotropin stimulation of the thyroid and reduces the goiter rate” was published by Michael B Zimmermann, et al. in the American Journal of Clinical Nutrition 2007;86 (1): 1040-1044

Introduction
Vitamin A deficiency (VAD) and Iodine Deficiency Disorders; (IDD) often coexist in developing countries. It is estimated that 32-50 % of school-age children in rural West and North Africa have both VAD and goiter. High-dose oral vitamin A supplementation (VAS) is a recommended strategy to control VAD in affected populations, many of whom are also iodine deficient. Conversely, many vitamin A deficient children in the developing world are consuming iodized salt. In the thyroid, VAD decreases thyroidal iodine uptake and iodine incorporation into thyroglobulin and increases thyroid size. The aim of the present study was to investigate the safety and efficacy of repletion with iodine or vitamin A alone, and in combination, in school-age children with concurrent VAD and iodine deficiency.

 Methods
The study was conducted in Limpopo Province in South Africa. The subjects were 5–14-y-old children from rural primary schools. All children in the schools were invited to participate. The only exclusion criteria were major chronic medical illnesses and recent consumption of iodine, vitamin A supplements, or both. The 6-mo study was a double-blind trial that used a 2 x 2factorial design. Children from the screening were randomly assigned to receive, at baseline and at 3 mo, one of the following:1) iodine _ placebo (IS group), 2) vitamin A (200 000 IU _ placebo (VA group), 3) both iodine and VA (IS_VAS group), or 4) placebo. At completion, all study children who had not received supplementation were given VAS, IS, or both

 Results
Overall, the children were reasonably well-nourished, as reflected by median height-for-age and weight-for-age z scores of _0.56 and _0.59, respectively. However, 12% of the children had a Serum Retinol (SR) concentration of 0.7 mol/L, indicating that VAD in this region is a moderate public health problem according to the WHO. There were no significant differences in any of the baseline variables or between the 4 groups after randomization. Both iodine and VA supplementation were effective. There were no significant treatment interactions between iodine and vitamin A.

Discussion
The data indicate that mild VAD does not reduce the efficacy of iodine supplementation to correct thyroid dysfunction in children with concurrent IDD and VAD. The major new finding of this study was that VAS alone in iodine-deficient children with mild VAD reduces circulating (thyroid-stimulating hormone (TSH), serum thyroglobulin, and thyroid size without significantly affecting thyroid hormone concentrations. The authors conclude that iodine prophylaxis is effective in controlling Iodine Deficiency, even in areas of poor VA status, and high-dose VAS is likely safe and effective in areas of mild Iodine Deficiency.

The findings suggest that high-dose VAS in a population can modify indicators of ID, such as thyroglobulin and goiter, independent of a change in iodine nutrition.