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Women’s health · Thyroid

Thyroid antibodies: what selenium and vitamin D can and can’t do

Hashimoto’s thyroiditis is the most common cause of an underactive thyroid in the US and is several times more common in women. Selenium and vitamin D lowered antibody levels in trials. Lower antibodies are not the same as feeling better, and neither replaces thyroid hormone when it is needed.

By Kymata Health Editorial Sources cited inline Prices checked Oct 29, 2026

Quick answer

The quick answer

  • In trials, selenium lowered TPO antibodies across 29 groups of patients, and lowered TSH slightly in people not on thyroid hormone.
  • Vitamin D lowered antibodies in small trials, with larger effects beyond 12 weeks; correct a low level first.
  • Lower antibodies have not been shown to slow progression or ease symptoms.
  • Iodine megadoses can worsen thyroid problems; most US adults get enough iodine from food.

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Story

A story you might recognize

Composite story built from common reader accounts; details changed. Not a testimonial.

She is 38. Her TSH is normal but her TPO antibodies came back high, and her doctor said to recheck in a year. Online, she found people saying to cut gluten, take iodine and buy an "adrenal and thyroid" blend.

She asked what had trials. Selenium had lowered antibodies; vitamin D was low on her test. She took both within their limits, skipped the iodine, and kept her yearly thyroid check.

The plan

The plan

  1. Step 1Know your numbers

    TSH, free T4 and TPO antibodies; recheck as your clinician advises, usually yearly with normal TSH.

  2. Step 2Check vitamin D

    Correct a low level within the upper limit.

  3. Step 3Consider selenium

    Within the upper limit, for a defined period, then review.

  4. Step 4Plan for pregnancy

    Positive antibodies raise the risk of thyroid problems in pregnancy; tell your clinician before trying.

The stack

The thyroid antibody stack

Two nutrients that lowered antibody levels in trials, within their upper limits. Evidence grade: A strong · B moderate · C limited · D preliminary.

  1. 01

    Selenium (selenomethionine)

    Lowered thyroid antibody levels in trials. It has not been shown to change how people feel or to replace thyroid hormone.

    What the research shows: A 2024 meta-analysis (29 cohorts, 2,358 people) found selenium lowered TPO antibodies and, in people not on thyroid hormone, TSH slightly. Whether lower antibodies translate into fewer symptoms or slower progression is not shown. (PMID 38243784)

    • Adult upper limit: 400 mcg a day from all sources (NIH Office of Dietary Supplements). Too much causes hair loss, brittle nails and a garlic odor on the breath.
    • A large trial in men linked long-term selenium to a higher risk of type 2 diabetes; do not take it indefinitely without a reason.

    In the studies

    • Trials in the 2024 meta-analysis mostly gave 200 mcg of selenium a day.

    A record of what researchers gave, in whom; not a dose for you.

    Evidencemoderate (Grade B)

    Quick pick · HerbsPro

    Brands that pay us are shown first in this list.

    NOW Foods Selenium, 100 mcg, 250 Tabs

    1 tablet: 100 mcg elemental selenium (from L-selenomethionine)

    $11.24price checked Oct 14, 2026 on HerbsPro’s site

    Shop at HerbsPro (paid link, opens in new tab)

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    Also from our partners

    Only brands that pay us are listed here.

  2. 02

    Vitamin D3 (if low)

    Correct a low level; lower antibodies are a possible bonus.

    What the research shows: A 2023 meta-analysis of 12 small trials (862 people with Hashimoto’s) found vitamin D lowered TPO and thyroglobulin antibodies. Trials were small and varied in dose. (PMID 38206745)

    • Adult upper limit: 4,000 IU (100 mcg) a day from all sources (NIH Office of Dietary Supplements).

    In the studies

    • Trials in the 2023 meta-analysis gave vitamin D for 12 weeks or more; doses varied, and the effect on antibodies was larger beyond 12 weeks.

    A record of what researchers gave, in whom; not a dose for you.

    Evidencelimited (Grade C)

    Quick pick · Momentous

    Brands that pay us are shown first in this list.

    Momentous Vitamin D3 2000 IU, 60 capsules

    1 capsule: 50 mcg (2,000 IU) vitamin D3 as plant-based cholecalciferol, in extra virgin olive oil; 60 servings

    $19.99price checked Oct 19, 2026 on Momentous’ site

    One-time
    $19.99
    Subscription
    $14.99

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    Also from our partners

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    Subscribe & save 25%. Pick “Subscribe 25% Off” on the product page; delivery every 1, 2 or 3 months; cancel or reschedule anytime.

    • Subscription price shown on each product card.
    • Our Momentous links apply the brand’s ambassador discount at checkout, so there is no code to type. Momentous sets any discount it applies; check the cart total before you pay.
    • Offer terms from Momentous’ site, checked Oct 8, 2026. Offers can change; the brand's checkout is final.

Listed picks above total $31.23 at one-time prices on the brands' own sites; most hold about a month of servings at the label's serving size.

Left out

What we left out, and why

Iodine and kelp supplements
Excess iodine can trigger or worsen thyroid dysfunction, especially in people with autoimmune thyroid disease. Kelp products vary enormously in iodine content.
"Thyroid support" glandulars
Some contain actual thyroid hormone in unknown amounts, which can cause dangerous over-replacement.
Biotin
High-dose biotin distorts thyroid blood tests and can lead to wrong diagnoses; stop it several days before testing.

Safety

Safety and interactions

  • Selenium: stay at or under the 400 mcg a day upper limit from all sources.
  • Never stop or change thyroid hormone without your prescriber.
  • Not medical advice. Check with your clinician or pharmacist before starting supplements if you take prescription medicines, are pregnant, trying to conceive or breastfeeding, or have kidney, liver or thyroid disease.
  • Supplements are not evaluated by the FDA to diagnose, treat, cure or prevent any disease.

Questions

Frequently asked questions

Does selenium lower thyroid antibodies?

Yes, in trials. A 2024 meta-analysis found selenium lowered TPO antibodies, mostly at 200 mcg a day (PMID 38243784). Whether that improves symptoms or slows progression is not shown.

Should I take iodine for Hashimoto’s?

No, not without a clinician. Excess iodine can worsen autoimmune thyroid disease, and most US adults get enough from food.

Does vitamin D help Hashimoto’s?

Small trials found vitamin D lowered thyroid antibodies, more so beyond 12 weeks. Correcting a low level is reasonable; stay under the 4,000 IU upper limit.

Sources

Sources

Studies were checked on PubMed on Oct 31, 2026. Product prices come from each brand's own site, read on Oct 29, 2026; each product shows the date its price was read.

  1. 1Huwiler VV et al. Selenium supplementation in Hashimoto thyroiditis: systematic review and meta-analysis of randomized clinical trials. Thyroid 2024 (opens in new tab)PMID 38243784
  2. 2Tang J et al. Effects of vitamin D supplementation on autoantibodies and thyroid function in Hashimoto’s thyroiditis: systematic review and meta-analysis. Medicine (Baltimore) 2023 (opens in new tab)PMID 38206745

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Educational only. Not medical advice.

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