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Open WellbeingWhat the studies actually measured

Skin, hair and nails

Biotin (vitamin B7)and Brittle nail severity

Both sources here measured lower brittle nail severity.

How sure anyone can be

Very low certainty, level 1 of 4

Any estimate here is very uncertain.

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

The numbers reported

No number has been put on this yet. Two sources recorded only which way the numbers went — for now, that is all we have here.

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.

  • Case series, 1993

    Very low certainty, level 1 of 4

    Brittle nails: response to daily biotin supplementation.

    Cutis. 1993;51(4):303-5. PMID:8477615.

    Number reported
    Not in the abstract
    Which way it went
    Lower
    Likely range
    Not in the abstract
    Source’s own words
    no effect size is reportable: the source gives only an uncontrolled responder count (22 of 35 who took daily biotin), which is not a change in nail severity and not a comparison against any control
    Who was studied
    Adult with brittle nails
    Compared with
    none (uncontrolled retrospective series)
    Amount taken
    Not in the abstract
    For how long
    Not in the abstract
    Disagreement between studies
    Not in the abstract
    Kind of record
    Journal article
    How this rating was reachedstarts at Very low, 2 steps down: risk of bias and imprecision
    1. Starts at Very low
    2. Risk of bias — already at Very low, the lowest rungthe abstract reports no risk-of-bias or quality appraisal, so study limitations cannot be ruled outNot in the abstract
    3. Imprecision — already at Very low, the lowest rungthe abstract reports no confidence interval for the estimateNot in the abstract
    4. Ends at Very low2 steps down.
    Checked, nothing to step it down for
    indirectness
    Inconsistency
    One study, so there was nothing to disagree

    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

  • Case series, 1989 · 71 participants

    Very low certainty, level 1 of 4

    [Treatment of brittle fingernails with biotin].

    Z Hautkr. 1989;64(1):41-8. PMID:2648686.

    Number reported
    Not in the abstract
    Which way it went
    Lower
    Likely range
    Not in the abstract
    Source’s own words
    no effect size is reportable: the source gives only a single-arm response rate (41 of the 45 evaluable patients, 91%, showed definite improvement), which is not a change in nail severity and not a comparison against any control
    Who was studied
    Adult with brittle nails
    Compared with
    none (uncontrolled)
    Amount taken
    2.5 mg/d
    For how long
    Not in the abstract
    Disagreement between studies
    Not in the abstract
    Kind of record
    Journal article
    How this rating was reachedstarts at Very low, 2 steps down: risk of bias and imprecision
    1. Starts at Very low
    2. Risk of bias — already at Very low, the lowest rungthe abstract reports no risk-of-bias or quality appraisal, so study limitations cannot be ruled outNot in the abstract
    3. Imprecision — already at Very low, the lowest rungthe abstract reports no confidence interval for the estimateNot in the abstract
    4. Ends at Very low2 steps down.
    Checked, nothing to step it down for
    indirectness
    Inconsistency
    One study, so there was nothing to disagree

    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

  • None gives a number at all, only which way it went.
  • Two give no likely range, so how precise those numbers are is unknown.
  • One do not say how many people took part.
  • Amount taken — One of Two readings: Not in the abstract.
  • For how long — Not in the abstract.

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

Still to read for Biotin (vitamin B7)

Four of the 13 things on our list for Biotin (vitamin B7) have no reading here yet:

  • Fasting insulin
  • Hair growth rate
  • Hepatic Fat Fraction
  • Vitamin B7 (Biotin)

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.