Micronutrient status, iodine nutrition and thyroid function: A systematic review

The thyroid gland is recognised for its role in maintaining human health. Thyroid hormone metabolism is dependent on many proteins and enzymes. Iodine is a key component of thyroid hormone biosynthesis while several other micronutrients are involved in maintaining thyroid function and include selenium, zinc, iron and vitamin A. This systematic review aimed to investigate the effect of micronutrient status and supplementation on iodine status and thyroid hormone concentrations. Electronic databases were searched from their inception to April 2016. Human studies published in English which reported data on micronutrient status and iodine status and/or thyroid hormone concentrations were included. Studies which examined the effect of micronutrient supplementation on thyroid hormone concentrations and/or iodine status were also included.Although observational evidence suggests that status of selenium, zinc and iron are positively associated with iodine status, data from randomised controlled trials fails to confirm this relationship. Conclusions on the effect of micronutrient supplementation on iodine and thyroid hormone status were hindered by the lack of studies and the heterogeneity in study designs.