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Open WellbeingWhat the studies actually measured

Hormones, thyroid and fertility

Seleniumand Thyroid-stimulating hormone (TSH)

Both sources here measured lower thyroid-stimulating hormone (TSH).

How sure anyone can be

Moderate certainty, level 3 of 4

Further research may change this.

The most certain of the two findings here; each record carries its own.

The numbers reported

One source’s range, drawn against its own line of no difference and scaled to its own numbers.

-0.43-0.21 standardised effect size-0.02

This range stays on one side of the no-difference line.

Bar the confidence interval — the range the true effect is likely to sit inNotch the number the source reportedLine where there would be no difference at all

Two sources, newest first

What we read is the published abstract, not the full paper, so a blank below may still be printed in the paper itself. A fixed rule worked this out from the source’s own fields. Nobody checked this rating by hand.

  • Systematic review, 2025

    Low certainty, level 2 of 4

    Clinical efficacy of selenium supplementation in patients with Hashimoto thyroiditis: A systematic review and meta-analysis.

    Medicine (Baltimore). 2025;104(35):e44043. doi:10.1097/MD.0000000000044043. PMID:40898469.

    Number reported
    -0.18 standardised effect size
    Which way it went
    Lower
    Likely range
    -0.35 to -0.01
    Source’s own words
    standardized mean difference in TSH vs comparison, 6-month time-point
    Who was studied
    Patients with hashimoto thyroiditis
    Compared with
    not stated in the abstract
    Amount taken
    Not in the abstract
    For how long
    183 days
    Disagreement between studies
    Not in the abstract
    Kind of record
    Journal article
    How this rating was reachedstarts at High, 2 steps down: risk of bias and imprecision
    1. Starts at High
    2. Risk of bias brought it down to Moderatethe abstract reports no risk-of-bias or quality appraisal, so study limitations cannot be ruled outNot in the abstract
    3. Imprecision brought it down to Lowthe abstract does not state how many participants were pooledNot in the abstract
    4. Ends at Low2 steps down.
    Checked, nothing to step it down for
    indirectness
    Inconsistency
    No disagreement reported, and no count of studies behind it

    Imprecision stops at the first check that applies; others may apply too.

    Source saved; quote checked byte-for-byte against it by software; no signature.

    Read the abstract on PubMed

  • Systematic review, 2024 · 7 studies pooled · 869 participants

    Moderate certainty, level 3 of 4

    Selenium Supplementation in Patients with Hashimoto Thyroiditis: A Systematic Review and Meta-Analysis of Randomized Clinical Trials.

    Thyroid. 2024;34(3):295-313. doi:10.1089/thy.2023.0556. PMID:38243784.

    Number reported
    -0.21 standardised effect size
    Which way it went
    Lower
    Likely range
    -0.43 to -0.02
    Source’s own words
    standardized mean difference in TSH vs control
    Who was studied
    Adult with hashimoto thyroiditis not on thyroid hormone replacement
    Compared with
    placebo
    Amount taken
    Not in the abstract
    For how long
    Not in the abstract
    Disagreement between studies
    I2 = 0%
    Kind of record
    Journal article
    How this rating was reachedstarts at High, one step down: imprecision
    1. Starts at High
    2. Imprecision brought it down to Moderatethe interval excludes no effect but spans a 22-fold range of effect size, from trivial to largeReported in the abstract
    3. Ends at ModerateOne step down.
    Checked, nothing to step it down for
    risk of bias and indirectness
    Inconsistency
    No high disagreement reported between the 7 studies it pooled

    Imprecision stops at the first check that applies; others may apply too.

    AI-reviewed & signed — an AI agent re-read this finding against the saved source and checked that the quote, the numbers, the units and the direction match it. No person read it. The owner authorised the agent to sign the batch with the owner's key, and every build rechecks that signature against these exact bytes.

    Read the abstract on PubMed

What is still missing from these readings

  • One do not say how many people took part.
  • Amount taken — Not in the abstract.
  • For how long — One of Two readings: Not in the abstract.

Something nobody wrote down is never a zero and never a guess.

Still to read for Selenium

Nine of the 20 things on our list for Selenium have no reading here yet:

  • Depression
  • Estimated VO2max
  • Free thyroxine (fT4)
  • Free triiodothyronine (fT3)
  • High-sensitivity CRP
  • Mood
  • Oxidative stress (F2-isoprostanes)
  • Plasma Selenium
  • Thyroglobulin Antibodies (TgAb)

Still to read means nobody here has got to it, not that it was tried and did nothing or that no research exists. A pairing on no list is not a gap: we never set out to read it.

Read next

This is a library, not advice. No recommendation, no dose, no diagnosis, no ranking. We never ask about your symptoms, and nothing here is tailored to you.