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 .
Effect of iron repletion and correction of iron deficiency on thyroid function in iron-deficient Iranian adolescent girls.
The aim of this study was to determine whether iron supplementation in iron-deficient adolescent girls would improve thyroid function . A double-blind clinical trial was performed in a region in southern I.R. Iran . A total of 103 iron deficient participants were chosen . In all , 94 participants successfully completed this study . Participants were r and omly assigned to one of two groups and treated with a 300 mg ferrous sulfate 5 times/week ( n = 47 ) and placebo 5 times/week ( n = 47 ) for 12 weeks . Blood sample s were collected and assayed for hemoglobin , hematocrit , serum ferritin , iron , total iron binding capacity ( TIBC ) , Thyroid stimulating hormone ( TSH ) , total thyroxine ( TT4 ) , total triiodothyronine ( TT3 ) , free thyroid hormones ( FT4 and FT3 ) , triiodothyronine resin uptake ( T3RU ) , reverse triiodothyronine ( rT3 ) , selenium and albumin concentrations . Statistical analysis was performed with parametric and non-parametric methods as appropriate . Data analysis revealed a significant increase in TT4 , TT3 , T3RU and a significant decrease in rT3 concentration in comparison to initial values in iron treated group ( 12 % , p<0.001 ; 3.5 % , p<0.001 ; 16 % , p<0.05 and 47 % , p<0.001 , respectively ) . At 12 week there were significant differences between control and placebo in TT4 , TT3 , T3RU and rT3 concentrations ( 9.9 vs 8.4 microg dL(-1 ) , 145.2 vs 130.4 microg dL(-1 ) , 32.5 vs 28.4 % and 23 vs 41 microg dL(-1 ) , respectively , all p<0.001 ) . Alterations in FT3 and TSH concentration were not significant , but concentration of FT4 revealed a significant difference between the beginning and the end of the study in iron treated group ( 10.3 vs 11.4 , p<0.001 ) . Iron supplementation improves some indices of thyroid function in iron-deficient adolescent girls
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 .