Selenium
Best for
Calm thyroid autoimmune activity
Likely strong benefit · 50–1000 mcg/day for 8–52 weeks · 4 meta-analyses , n=5.1k
58 papers · 9 claims · 120 outcomes scored · 6 positive
Evidence summary
Evidence summary
Likely strong benefitSelenium shows a likely strong benefit for calming autoimmune thyroid activity in Hashimoto's thyroiditis, with additional benefit for sperm quality, while other uses remain weaker.
- Across 9 studies (n=5,146), selenium lowered thyroid autoantibody levels, a change consistent with meaningful improvement in Hashimoto's thyroiditis.2
- Male infertility trials also report improved sperm quality, but thyroid autoimmunity is the clearest signal across the evidence base.3
- Useful doses sit close to the upper intake limit, so excess selenium can become a real safety issue.1
Outcomes
What selenium actually does, by outcome
Each row is one outcome with effect size, evidence base, the dose that worked in trials, and time to first effect. Magnitude tiers come from native-unit MCID where available, Cohen's d otherwise.
Reduces the antibodies that attack thyroid tissue in Hashimoto's.
Less oxidative damage to your cell membranes, proteins, and DNA.
Essential mineral blood levels rise into optimal range, confirming absorption.
Raises count, movement, and normal shape in your semen analysis.
Keeps the gland that controls your metabolism producing at the right level.
Fewer diagnoses, slower precancerous changes, steadier PSA.
Reduces cold intolerance, fatigue, and brain fog from underactive thyroid.
Keeps your thyroid stable when pregnancy doubles its workload.
Repairs sun-damaged skin cells before they turn precancerous.
Forms & standardisation
The best-studied forms are selenium yeast and L-selenomethionine. Those are the labels to look for if you want to match the thyroid and fertility trials, because those studies used those forms most often.123 Sodium selenite also appears in research, but the strongest consumer-facing evidence clusters around yeast or selenomethionine.14
Risk profile
Adverse events and known drug interactions
Safety events
Drug interactions
Frequently asked
Common questions
Is selenium good for Hashimoto's thyroiditis?
How much selenium should I take?
Does selenium improve sperm quality?
What form of selenium is best?
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