Although observational evidence suggests that concentrations of selenium , zinc , and iron are positively associated with iodine status , data from r and omized controlled trials fail to confirm this relationship .
Context The metabolism of thyroid hormones , which are essential for normal development , involves many proteins and enzymes .
It requires iodine as a key component but is also influenced by several other micronutrients , including selenium , zinc , iron , and vitamin A. Objective This systematic review was design ed to investigate the effect of micronutrient status and supplementation on  iodine status and thyroid hormone concentrations .
Vitamin A supplementation in iodine-deficient African children decreases thyrotropin stimulation of the thyroid and reduces the goiter rate.
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 r and omized , 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 ( TT(4 ) ) , 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 TT(4 ) . 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 TSHbeta gene , VAS can decrease excess TSH stimulation of the thyroid and thereby reduce the risk of goiter and its sequelae
Although observational evidence suggests that concentrations of selenium , zinc , and iron are positively associated with iodine status , data from r and omized controlled trials fail to confirm this relationship .
Context The metabolism of thyroid hormones , which are essential for normal development , involves many proteins and enzymes .
It requires iodine as a key component but is also influenced by several other micronutrients , including selenium , zinc , iron , and vitamin A. Objective This systematic review was design ed to investigate the effect of micronutrient status and supplementation on  iodine status and thyroid hormone concentrations .