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 .
The Effect of Vitamin A Supplementation on Thyroid Function in Premenopausal Women
Objective : Vitamin A and its retinoid derivates play an important role in regulation of normal growth and development . Vitamin A has been shown to regulate thyroid hormone metabolism and inhibit thyroid-stimulating hormone ( TSH ) secretion via down regulation of TSH-β gene expression ; however , the effect of vitamin A on thyroid function in obese individuals who are at higher risk of sub clinical hypothyroidism is still unclear . In the present study we investigate the impact of vitamin A supplementation on thyroid function in obese women . Method : A 4-month r and omized , double blind controlled trial was conducted among 84 healthy women aged 17–50 years old : 56 were obese ( body mass index [ BMI ] 30–35 kg/m2 ) and 28 were nonobese ( BMI 18.5–24.9 kg/m2 ) . Obese women were r and omly allocated to receive either vitamin A ( 25,000 IU/d retinyl palmitate ) or placebo .  Nonobese women  received vitamin A. At baseline and 4 months after intervention , serum concentrations of TSH , total thyroxine ( T4 ) , total triiodothyronine ( T3 ) , retinol-binding protein ( RBP ) , and transthyretin ( TTR ) were measured . Results : Baseline concentrations of thyroid hormones , RBP and TTR were not significantly different between groups . Vitamin A caused a significant reduction in serum TSH concentrations in obese ( p = 0.004 ) and nonobese ( p = 0.001 ) groups . Serum T3 concentrations also increased in both obese and nonobese vitamin A – treated groups ( p < 0.001 ) . Serum T4 decreased in all 3 groups after treatment . The results showed a significant reduction in serum RBP in the obese group after vitamin A supplementation ( p = 0.007 ) , but no significant change was seen in serum TTR . Conclusions : Serum TSH concentrations in vitamin A – treated subjects were significantly reduced ; therefore , vitamin A supplementation might reduce the risk of sub clinical hypothyroidism in premenopausal women
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 .