vitamin
Biotin
Vitamin B7/vitamin H, a water-soluble B-vitamin serving as a coenzyme for carboxylase enzymes. Supports keratin production for healthy hair, skin, and nails, and assists in macronutrient metabolism.
Marketing vs Evidence
What brands claim
"Promotes healthy hair, skin, and nails" — found on nearly every beauty supplement label.
What the research shows
Only benefits people with a genuine biotin deficiency, which is uncommon in healthy adults eating a varied diet. No clinical evidence it improves hair or nail growth in non-deficient individuals. Most products dose 10–100× the daily requirement.
What it’s good for
Biotin for Brittle Nails
Mixed7 studies · 3 supporting · 1 against
4 safety notes
Thickens the nail plate by improving how keratin knits together — about 25% thicker in trials.
Dose: 2500–5000 mcg
Biotin for Hair Thinning
No Benefit2 studies · 0 supporting · 1 against
4 safety notes
How it was tested: Two weeks of 5 mg a day did nothing for hair length or coverage in healthy men.
Biotin helps build keratin, the protein hair is made of.
Dose: 2500–5000 mcg
Biotin for Muscle Cramps
Not verified1 study · 1 supporting · 0 against
4 safety notes
Dose: 1 mg
Tested as: Oral biotin 1 mg daily
Why we could not verify it: We found 1 study on this. We have not finished reading them yet, so we are not ready to say either way.