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Vitamin A supplementation in iodine-deficient African children decreases thyrotropin stimulation of the thyroid and reduces the goiter rate^1,2,3

¹ From the Laboratory for Human Nutrition, Swiss Federal Institute of Technology, Zürich, Switzerland (MBZ and RB); the Division of Human Nutrition, Wageningen University, Wageningen, Netherlands (MBZ); the Medical Research Council, Cape Town, South Africa (PLJ and SS); and the University of Venda, Thohoyandou, South Africa (NSM, LFM, and XM)

Background: Vitamin A (VA) deficiency (VAD) and iodine deficiency (ID) often coexist in children in Africa. VAD may affect thyroid function and the response to iodine prophylaxis.

Objective: The aim was to investigate the effects of supplementation with iodine or VA alone, and in combination, in children with concurrent VAD and ID.

Design: A 6-mo randomized, double-blind, 2 x 2 intervention trial was conducted in 5–14 y-old South African children (n = 404), who, on average, had mild-to-moderate VAD and ID. At baseline and after 3 mo, children received 1) iodine (191 mg I as oral iodized oil) + placebo (IS group), 2) VA (200000 IU VA as retinyl palmitate) + placebo (VAS group), 3) both iodine and VA (IS+VAS group), or 4) placebo. At baseline, 3 mo, and 6 mo, urinary iodine (UI), thyroid volume, thyrotropin (thyroid-stimulating hormone; TSH), total thyroxine (TT₄), thyroglobulin, serum retinol (SR), and retinol-binding protein (RBP) were measured.

Results: SR and RBP increased significantly with VA supplementation (P < 0.05). For UI, SR, and RBP, there were no significant treatment interactions between iodine and vitamin A. The 3-factor and all three 2-factor interactions were significant for thyroid volume, TSH, and thyroglobulin (P < 0.001), whereas none of these interactions were significant for TT₄. There was a clear effect of VAS without IS on TSH, thyroglobulin, and thyroid volume; all 3 variables decreased significantly (P < 0.05).

Conclusions: Iodine prophylaxis is effective in controlling ID in areas of poor vitamin A status. VA supplements are effective in treating VAD in areas of mild ID and have an additional benefit—through suppression of the pituitary TSHß gene, VAS can decrease excess TSH stimulation of the thyroid and thereby reduce the risk of goiter and its sequelae.

Key Words: Vitamin A • iodine • supplementation • deficiency • Africa • children