Zinc, Selenium and Thyroid Function in Women

Two micronutrients that are very important for thyroid hormone metabolism are zinc and selenium. Zinc is actually used for more than 300 enzymes in the body and is also required for proper hormone function – including our all-important thyroid hormone!

T3 is our active thyroid hormone – the one responsible for running our metabolism. The receptors for T3 contain zinc binding proteins – as such, zinc is needed for both the formation and also function of T3 in our bodies and in addition to this, TRH (thyroid releasing hormone) which is secreted from our hypothalamus (brain) requires zinc to work as well. Zinc deficiency will inhibit our thyroid hormone function in a variety of ways and this is why getting enough is very important for those who have hypothyroidism.

Selenium, we all know is one of the most important micronutrients for thyroid function. It can reduce thyroid antibodies, and plays a crucial role in thyroid hormone synthesis. It also shields the thyroid against damage as it’s a key component of glutathione peroxicase – our thyroid’s antioxidant protector. In fact, the thyroid has the highest concentration in the entire body of selenium.

A recent randomized double blind controlled trial investigated the individual or combined effects of zinc and selenium supplementation on a group of 68 hypothyroid female patients who were overweight or obese and taking l-thyroxine replacement therapy (aka Synthroid). Patients were given 30mg of zinc plus placebo, or 200mcg of selenium plus placebo, both zinc and placebo, or two placebo tablets.

The supplementation was continued for a period of 12 weeks. Measurements of common thyroid hormones were taken.

  • Free T4 – this increased in all groups after intervention however it was significant in only the zinc and selenium group.
  • Free T3 – The overall changes in free T3 from the baseline values were significant in the groups taking zinc alone, and zinc and selenium together.
  • FreeT3: Free T4 -the ratio of free T3 and Free T4 were included in this study to reflect conversion, as T4 must be converted to the active T3 to be metabolically active in the tissues. The zinc group showed an increase in this ratio.

Interestingly, the author notes that the subjects in this study were measured to be sufficient and even better than average, indicating that the improvement by selenium may not be as marked as it would be in people who are selenium deficient. In addition the study did not use selenomethionine, (instead using yeast derived selenium) and selenomethionine has been shown in previous studies to elevate selenium status more effectively. Another factor noted was that selenium must be supplemented for a period of 6 months or more to increase selenium concentrations in healthy adults.

As such, it’s quite possible (as indicated by numerous previous studies) that selenium could provide even more benefit than is noted in this study for patients suffering with hypothyroidism. This may be even more true for patients suffering with Hashimoto’s for whom selenium has been found to significantly reduce the antibody counts.

  • Zinc can deplete copper, particularly if given in high doses (especially over 40 mg per day).
  • Zinc absorption can be reduced by eating phytates – which are present in grains, and legumes. Some people avoid these foods, however sprouting and soaking them has been shown to reduce the amount of phytates – in any case they should not be eaten with every meal.
  • People with celiac disease or intestinal conditions may not be able to absorb zinc.
  • Excess zinc may aggravate hair loss in some susceptible individuals, particularly those who have PCOS so it should be implemented with caution in this group
  • Selenium can be toxic and an upper limit of 400mcg has been recommended. Signs of toxicity include nail changes, skin changes, tingling in the hands and feet.
  • Selenomethionine is the best form according to current research.
  • Whenever a multivitamin contains iodine, it should contain selenium as well – as selenium limits damage from excessive amounts of iodine due to it’s cellular protection effects.
  • Oysters 74 mg per 3 oz
  • Roast Beef 7 mg per 3 oz
  • Pork 2.9 mg per 3 oz
  • Chicken 2.4 mg per 3 oz
  • Brazil Nuts – by far the richest at 544 mcg for 6-8 nuts though selenium content of brazil nuts is not consistent enough for treatment.
  • Fish – 50 mcg per serving of 3 oz
  • Liver – 28 mcg per serving of 3 oz


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  10. National Institutes of Health Food and Nutrition Information Center