What the Research Actually Says About Selenium and Thyroid Antibodies

If you have spent any time in a Hashimoto's community, you have seen selenium recommended over and over. Unlike most supplement advice, this one is actually backed by randomized controlled trials — which is rare in the supplement world.

Multiple studies have found that 200 mcg of selenium per day, usually as selenomethionine, can lower thyroid peroxidase (TPO) antibodies over several months. The effect is most consistent in people who are selenium-deficient to begin with.

That said, antibodies are a marker, not the whole story. Lower antibodies do not always translate to feeling better, and selenium does not replace thyroid medication. The honest takeaway: selenium is a reasonable, low-risk foundation supplement at 200 mcg, but it is not a miracle.

What to avoid: doses above 400 mcg per day, which provide no extra benefit and can become toxic over time. Stick to the form and dose the research used.