Skip to content
Winnowleaf home

Does selenium help Hashimoto's?

Not in a way you would feel. Selenium lowers thyroid antibody levels a little, but in the largest trial, 412 adults with Hashimoto's on levothyroxine took 200 mcg a day or a placebo for a year, and quality of life improved equally in both groups, with no change in their thyroid medicine dose (grade B). More is not better: the adult upper limit is 400 mcg a day.

Last reviewed

How we grade evidenceEditorial policy

What the studies found

  • Grade B. In a year-long trial of 412 adults with Hashimoto's who were taking levothyroxine, 200 mcg of selenium a day did not improve quality of life more than a placebo. Antibody levels ended a little lower with selenium, but the thyroid medicine dose did not change. (Larsen 2024)
  • Grade B. Across 35 trials, selenium lowered thyroid peroxidase antibodies (the antibodies that attack the thyroid; 29 trial groups, 2,358 people), though results varied a lot from trial to trial. It did not change thyroid hormone levels (T3 and T4). (Huwiler 2024)
  • Grade C. In people not yet on thyroid medicine, results on TSH (the pituitary's signal to the thyroid) disagree: one review found a small drop in 869 people, while an earlier review of 9 trials found no change in TSH, quality of life or the ultrasound picture. (Huwiler 2024, Winther 2017)

Who should be careful

  • The adult upper limit for selenium is 400 mcg a day from food and pills combined. Too much over time can cause hair loss, brittle nails, a garlic smell on the breath and a metallic taste. One Brazil nut can hold 68 to 91 mcg (NIH ODS).
  • In a trial of 1,202 adults followed for about 7.7 years, 200 mcg of selenium a day went with more new cases of type 2 diabetes than placebo (58 against 39). (Stranges 2007)
  • Don't change your levothyroxine dose on your own; ask the prescriber, and recheck thyroid levels as they advise.
  • Pregnant or breastfeeding, or under 18: ask a clinician first.

Try first

  • Thyroid hormone replacement when your thyroid is underactive. Levothyroxine is the standard treatment in the American Thyroid Association's guideline, adjusted with blood tests. (Jonklaas 2014)
  • If you still feel unwell on a steady dose, ask your doctor to look for other causes before adding supplements.

Sources

  1. Larsen C, et al. Selenium supplementation and placebo are equally effective in improving quality of life in patients with hypothyroidism. Eur Thyroid J. 2024. PubMed 38215286 · doi:10.1530/ETJ-23-0175
  2. Huwiler VV, et al. Selenium Supplementation in Patients with Hashimoto Thyroiditis: A Systematic Review and Meta-Analysis of Randomized Clinical Trials. Thyroid. 2024. PubMed 38243784 · doi:10.1089/thy.2023.0556
  3. Winther KH, et al. Insufficient documentation for clinical efficacy of selenium supplementation in chronic autoimmune thyroiditis, based on a systematic review and meta-analysis. Endocrine. 2017. PubMed 27683225 · doi:10.1007/s12020-016-1098-z
  4. Stranges S, et al. Effects of long-term selenium supplementation on the incidence of type 2 diabetes: a randomized trial. Ann Intern Med. 2007. PubMed 17620655 · doi:10.7326/0003-4819-147-4-200708210-00175
  5. Jonklaas J, et al. Guidelines for the treatment of hypothyroidism: prepared by the american thyroid association task force on thyroid hormone replacement. Thyroid. 2014. PubMed 25266247 · doi:10.1089/thy.2014.0028