vitamin · for brittle nails
Biotin
Thickens the nail plate by improving how keratin knits together — about 25% thicker in trials.
Say that in clinical terms
Biotin enhances nail plate thickness by stimulating keratinocyte growth and improving the cross-linking of keratin proteins in the nail matrix. Clinical trials show 25% increase in nail thickness with supplementation.
How strong is the research?
In 61 patients, biotin alone fixed the problem in 10% of cases — against 70% for the alternative.
7 papers read, 3 supporting, 1 against.
Who was studied: Patients attending a nail clinic with diagnosed brittle nail syndrome.
How much to take
daily
2500–5000 mcg
Biotin is the most studied supplement for nail brittleness. Allow 6-9 months for full nail plate replacement.
Before you take it
- No Tolerable Upper Intake Level (UL) has been established by NIH ODS/FNB for biotin. The FNB concluded that no human toxicity from high biotin intake has been documented; doses up to 200 mg/day orally have been studied without adverse direct effects. No UL can be derived from current evidence.
- Biotin-streptavidin immunoassay interference: At supplemental doses of 5 mg (5,000 mcg) and above, biotin causes clinically significant false laboratory results in immunoassays using biotin-streptavidin capture technology. Affected tests include cardiac troponin (falsely LOW — the FDA received one patient death report from a missed cardiac diagnosis), TSH (falsely suppressed, mimicking thyrotoxicosis or falsely elevated), free T4, free T3, and sex hormone panels. The FDA issued safety communications in November 2017 and November 2019. Even a single 10 mg dose can interfere with thyroid function tests administered within 24 hours. Patients must disclose biotin use to clinicians before any blood draw and should wait at least 8 hours (up to 72 hours for some assays) after last dose before blood collection.
- Anticonvulsant-biotin depletion: Carbamazepine, primidone, phenytoin, and phenobarbital — after at least 1 year of treatment — significantly lower serum biotin levels by increasing biotin catabolism and inhibiting intestinal biotin absorption. Patients on these anticonvulsants may have higher biotin requirements.
- Raw egg white consumption depletes biotin: avidin in raw (not cooked) egg whites binds dietary biotin in the GI tract and prevents absorption. Sustained consumption of raw eggs can induce biotin deficiency.
When to take it
Best taken: morning
What we make of it
A look back at clinic records, not a trial — and the 25% figure comes from somewhere else.
The detail
What we cite is a retrospective review of patients attending a nail clinic rather than a controlled trial. The 25% thickness figure quoted in our mechanism comes from a separate Swiss microscopy study, not from this one.