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 .
Selenium, zinc, and thyroid hormones in healthy subjects
Iodothyronine 5′ deiodinase , which is mainly responsible for peripheral T3 production , has recently been demonstrated to be a selenium (Se)-containing enzyme . The structure of nuclear thyroid hormone receptors contains Zinc ( Zn ) ions , crucial for the functional properties of the protein . In the elderly , reduced peripheral conversion of T4 to T3 with a lower T3/T4 ratio and overt hypothyroidism are frequently observed . We measured  serum Se and RBC GSH-Px ( as indices of Se status ) , circulating and RBC Zinc ( as indices of Zn status ) , thyroid hormones and TSH  in 109 healthy euthyroid subjects ( 52 women , 57 men ) , carefully selected to avoid abnormally low thyroid hormone levels induced by acute or chronic diseases or calorie restriction . The subjects were subdivided into three age groups . To avoid under- or malnutrition conditions , dietary records were obtained for a sample of 24 subjects , r and omly selected and representative of the whole population for age and sex .  Low T3/T4 ratios and reduced Se and RBC GSH-Px activity were observed only in the older group . A highly significant linear correlation between the T3/T4 ratio and indices of Se status was observed in the older group of subjects ( r=0.54;p<0.002 , for Se;r=0.50;p<0.002 , for RBC GSH-Px ) . Indices of Zn status did not correlate with thyroid hormones , but RBC Zn was decreased in older as compared with younger subjects . We concluded that reduced peripheral T4 conversion is related to impaired Se status in the elderly
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 .