Supplements and thyroid
Supplements for Hashimoto’s: What the Evidence Says
Reviewed by a qualified clinician · analysed at UKAS-accredited UK labs (ISO 15189)
Last reviewed August 20267 min read
Every Helvy guide is written by our health editors, then checked by a qualified clinician before it goes live and re-checked as the science moves. We name clinical roles, not individuals, until each reviewer has agreed to be credited publicly. This is wellness guidance to help you understand your own data, not a diagnosis.
QUICK ANSWER
Selenium has the most trial evidence: pooled randomised trials show it lowers thyroid antibody levels. Vitamin D and myo-inositol did not, over six months. Cochrane still calls the evidence incomplete. Iodine is the one to be careful with. Before starting anything, measure TSH, Free T4 and Free T3.
Most Hashimoto’s supplement advice online comes from one of two places. Either a forum stack post, or a site selling the supplement. Neither tells you what the trials measured, or how small they were.
Here is the pooled evidence, one supplement at a time. Then the part almost nobody covers: which of your own numbers to see first.
By the Helvy Medical Team · Reviewed by a qualified clinician · 7 min read
As of August 2026. Reflects the 2024 network meta-analysis in Frontiers in Endocrinology, the Cochrane review of selenium, and current NHS guidance on iodine and selenium intake.
1. What do the trials actually show?
Three supplements come up again and again: selenium, vitamin D and myo-inositol. In 2024 a research team pooled the randomised trials on all three and compared them in a single analysis. It was published in Frontiers in Endocrinology.
Ten randomised trials went in. All were in people whose thyroid hormone levels were still normal. The thing being measured was antibody level, not how anyone felt day to day. Hold onto that distinction.
SELENIUM — THE ONLY CLEAR SIGNAL
Against placebo, selenium lowered thyroid peroxidase antibodies (TPOAb, the marker of autoimmune thyroid activity) and thyroglobulin antibodies. The pooled effect sizes were large. The confidence intervals were also wide, because the trials were small and differed a lot.
VITAMIN D — NO ANTIBODY EFFECT AT SIX MONTHS
Over a six-month treatment period, vitamin D on its own did not significantly lower either antibody in the pooled analysis. That is a narrower claim than “vitamin D does nothing”. It is still less than most stack posts imply.
MYO-INOSITOL — NOT ON ITS OWN
Myo-inositol alone did not reduce either antibody. Paired with selenium it nudged TSH down, but that six-month result was not statistically significant.
Cochrane looked at the selenium question separately and was blunter about it.
“Evidence to support or refute the efficacy of selenium supplementation in people with Hashimoto’s thyroiditis is incomplete.”
— Cochrane Database of Systematic Reviews, CD010223
So the honest summary is narrow. One supplement moved one blood marker, in small trials, with a lot of noise around the result. None of this is a treatment, and none of it replaces what your GP prescribes.
2. What should you test before you start?
Most people start a thyroid stack without ever having seen their full thyroid picture. That is not carelessness. It is how UK testing is designed to work.
NICE guideline NG145 tells clinicians to measure TSH first. Free T4 is added only if TSH sits above the reference range. Free T3 is added only if TSH sits below it. Our guide to the TSH blood test explains that cascade.
The logic is sound for a screening test. It also means a normal TSH ends the investigation. You never see Free T4, and you almost never see Free T3.
If you are about to spend six months and real money on a stack, knowing your starting numbers beats guessing at them.
Our Thyroid & Vital Organs panel (£159) measures TSH, Free T4 and Free T3, alongside kidney, liver and cholesterol markers, from a home finger-prick sample. Vitamin D sits in a different one: General Energy & Wellness (£149) covers vitamin D with TSH, Free T4, B12 and magnesium.
One honest limit. Thyroid antibodies are not in any Helvy panel. TPO and thyroglobulin antibodies are the markers that define autoimmune thyroid disease, and they need to come from your GP. Our guide to a thyroid antibodies blood test covers what they measure and why.
A blood test measures markers. It does not diagnose anything, and a result that worries you belongs with your GP.
3. Which supplement should you be careful with?
Iodine. It gets recommended constantly, and it has the clearest reason for caution.
Your thyroid needs iodine to make hormone. That true fact gets stretched into “more must be better”. It does not work that way.
“Taking high doses of iodine for long periods of time could change the way your thyroid gland works.”
— NHS, Vitamins and minerals: Iodine
The NHS figure for adults is 140 micrograms a day. It adds that 0.5mg or less a day from supplements is unlikely to cause harm. Most UK diets already reach the target through dairy and fish.
A February 2026 review of Hashimoto’s management puts it plainly: excessive iodine intake increases the risk of autoimmune thyroid disease, and the authors advise avoiding a high iodine diet.
Kelp and seaweed capsules are the usual route to a high dose. The iodine content varies enormously between products, and some sit far above the NHS number. Read the label before you read the reviews.
Selenium has a ceiling too. The NHS puts adult need at 75 micrograms a day for men and 60 for women, and says 350 micrograms or less a day from supplements is unlikely to cause harm. Too much causes selenosis, which starts with hair and nail loss. The trials used 200 micrograms.
4. How would you know if it is working?
The trials ran for three to six months. That is the timescale to think in. A fortnight of feeling brighter tells you nothing.
Track what you can actually measure. TSH, Free T4 and Free T3 describe thyroid function. Vitamin D responds to a vitamin D supplement. Both are readable on a repeat sample, so a before and an after are comparable.
Take the sample the same way each time. Morning, and before your levothyroxine dose if you take one. Our guide to when to take a hormone blood test covers the timing rules that keep results comparable.
Keep your GP in the loop, especially on levothyroxine. A supplement that shifts your thyroid numbers is something your prescriber needs to know about. See levothyroxine blood tests for what gets monitored and how often.
One marker people miss: cholesterol. A slow thyroid tends to push it up, which is why the Thyroid & Vital Organs panel includes a lipid profile. Our guide to a cholesterol blood test explains those numbers.
For the wider picture, start at the thyroid guides hub.
Frequently asked questions
Does selenium lower thyroid antibodies?
In the pooled trials, yes. The 2024 network meta-analysis found selenium lowered both TPO and thyroglobulin antibodies against placebo. Cochrane, reviewing the same question, called the evidence incomplete. What a lower antibody level means for how you feel is still unsettled.
How much selenium is safe to take?
The NHS says adults need 75 micrograms a day for men and 60 for women, and that 350 micrograms or less a day from supplements is unlikely to cause harm. The trials used 200 micrograms. Doses above the NHS figure are worth discussing with your GP first.
Should I take iodine if I have Hashimoto’s?
The NHS warns that high doses over long periods could change how your thyroid gland works, and a 2026 review advises people with Hashimoto’s to avoid a high iodine diet. Kelp and seaweed capsules are the usual source of a high dose. Raise it with your GP before starting one.
Does vitamin D help Hashimoto’s?
In the pooled six-month data, vitamin D on its own did not significantly lower either thyroid antibody. That is a specific finding about antibodies, not a verdict on vitamin D generally. You can measure your own level in our General Energy & Wellness panel.
Which blood test should I get before starting supplements?
A full thyroid picture: TSH, Free T4 and Free T3. Our Thyroid & Vital Organs panel measures all three from a home finger-prick sample. Thyroid antibodies are not in any Helvy panel, so ask your GP about those.
Measure it, then decide
Our Thyroid & Vital Organs panel (£159) measures TSH, Free T4 and Free T3, plus kidney, liver and cholesterol markers. Home finger-prick kit, results in about 5 working days, from UKAS-accredited UK laboratories.
Medical disclaimer:This content is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Hashimoto’s thyroiditis is diagnosed and managed by a doctor. The studies cited measure population-level effects on blood markers and may not predict an individual response. Do not start, stop or change any supplement or treatment based solely on this article, particularly if you take levothyroxine. Consult your GP or a qualified healthcare professional. All Helvy blood tests are processed by UKAS-accredited UK laboratories to ISO 15189.
Last updated: August 2026 · By Helvy · Medically analysed at UKAS-accredited UK laboratories
RELATED READING