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 .
Minimal impact of excess iodate intake on thyroid hormones and selenium status in older New Zealanders.
OBJECTIVE Iodine deficiency has re-emerged in New Zeal and , while selenium status has improved . The aim of this study was to investigate the effects of excess iodine intake as io date on thyroid and selenium status . METHODS In a r and omized controlled trial on older people ( mean±s.d . 73±4.8 years ; n=143 ) , two groups received > 50 mg iodine as io date /day for 8 weeks because of supplement formulation error , either with 100 μg selenium ( Se+highI ) or without selenium ( highI ) . Four other groups received 80 μg iodine as io date /day with selenium ( Se+lowI ) or without selenium ( lowI ) , selenium alone ( Se+ ) , or placebo . Thyroid hormones , selenium status , and median urinary iodine concentration ( MUIC ) were compared at weeks 0 , 8 , and 4 weeks post-supplementation . RESULTS MUIC increased nine- and six-fold in Se+highI and highI groups , decreasing to baseline by week 12 . Plasma selenium increased in selenium-supplemented groups ( P<0.001 ) . The level of increase in whole blood glutathione peroxidase ( WBGPx ) in the Se+highI group was smaller than Se+ ( P=0.020 ) and Se+lowI ( P=0.007 ) groups . The decrease in WBGPX in the highI group was greater than other non-selenium-supplemented groups , but differences were not significant . Ten of 43 participants exposed to excess io date showed elevated TSH ( hypothyroidism ) at week 8 . In all but two , TSH had returned to normal by week 12 . In three participants , TSH decreased to < 0.10 mIU/l ( hyperthyroidism ) at week 8 , remaining low at week 12 . CONCLUSIONS Excess io date induced hypothyroidism in some participants and hyperthyroidism in others . Most abnormalities disappeared after 4 weeks . Excess io date reduced WBGPx activity and result ed in smaller increases in WBGPx after selenium supplementation
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 .