Selenium supports your thyroid

Selenium is part of the enzymes that switch thyroid hormone on and off. Whether extra selenium from a supplement does more has been tested mainly in people with autoimmune thyroid disease, and what it does depends on the disease and on what is measured. In Hashimoto's thyroiditis, a 2024 review of 35 studies found that selenium lowered thyroid peroxidase antibodies, a marker of the autoimmune process rather than a measure of how the thyroid works, and, in people not yet taking thyroid hormone, lowered TSH slightly, with no change in thyroid hormone levels. The largest trial since that review, 412 adults already taking levothyroxine, found no difference from placebo in quality of life after 12 months, and selenium made no difference to their levothyroxine dose.

In Graves' disease, the largest trial, 430 adults, found that selenium added to antithyroid drugs made no difference to whether the overactive thyroid went into remission. In mild Graves' eye disease, a 2011 trial of 159 people found that selenium was associated with better quality of life and slower progression after six months, and a 2026 review of five trials found lower eye disease activity scores but no clear difference in quality of life or vision. A 2025 trial in South Korea, where selenium intake is adequate, found no difference at six months. The 2022 statement of the American and European thyroid associations says a single six-month course may be considered for mild, active eye disease, particularly where selenium intake is low. In pregnancy, two small trials in women with thyroid antibodies found fewer thyroid problems or lower antibodies after delivery with selenium, and in 2017 the American Thyroid Association made a weak recommendation against selenium for pregnant women with these antibodies. In 491 older adults with normal thyroid function, five years of selenium lowered TSH and free thyroxine slightly, by amounts that grew with dose; the trial measured hormone levels, not energy, weight or metabolism. Most trials used 200 micrograms a day. The US upper limit for adults is 400 micrograms a day from all sources, set to avoid selenosis, selenium toxicity, and the European Food Safety Authority set 255 micrograms a day for all adults in 2023.

Whether lowering thyroid peroxidase antibodies changes how a person feels, or the course of the disease over years, has not been tested in these trials. The 2024 review found that the size of the antibody drop varied widely from trial to trial, found side effects similar between selenium and control groups, and rated its overall certainty moderate. In the 412-person trial, antibodies were somewhat lower with selenium at 12 months, quality of life improved in both groups with no difference between selenium and placebo on any scale, and selenium made no difference to levothyroxine dose. The UK's national guideline on thyroid disease says its committee was unable to make recommendations on selenium supplements because of a lack of evidence.

In the 430-person Graves' trial, run over 24 to 30 months, the disease had not gone into remission in 54.6% of people on selenium and 53.3% on placebo, and selenium made no difference to quality of life. The 2011 eye disease trial was run by a European research group and compared selenium with both placebo and an anti-inflammatory drug, and the 2025 trial was open-label.

The pregnancy trials enrolled women with thyroid antibodies, who are prone to thyroid problems after giving birth. In one, thyroid problems after delivery affected 28.6% of women on selenomethionine and 48.6% on placebo (77 and 74 women), and lasting underactive thyroid 11.7% and 20.3%; whether that trial was blinded could not be confirmed. The second, of 45 women, found lower antibodies after delivery. The European upper limit of 255 micrograms a day applies during pregnancy and breastfeeding.

In the Hashimoto's and Graves' trials, selenium was taken alongside standard treatment, not in place of levothyroxine or antithyroid drugs. Most trials gave selenomethionine, selenium yeast or sodium selenite, often to people whose selenium intake was marginal, so the results may not carry over to people who already get enough from their diet. The individual trials cited here enrolled adults, and children and teenagers are further from what was studied.