Biotin

vitamin

What is it

Biotin (also called vitamin B7 or vitamin H) is a water-soluble B-vitamin that acts as a coenzyme for five essential carboxylase enzymes. These enzymes carry out key steps in metabolism of carbohydrates, fats, and certain amino acids.

How it works

After absorption in the small intestine, biotin is attached to carboxylase enzymes by the enzyme holocarboxylase synthetase. These activated carboxylases catalyze reactions critical to gluconeogenesis (making glucose from non-carbohydrate sources), fatty acid synthesis, and breakdown of branched-chain amino acids like leucine. Biotin also influences gene expression through histone modifications and supports the formation of keratin, the structural protein that makes up hair and nails. This last role is the basis for biotin's reputation in beauty supplements, though the clinical evidence for cosmetic benefits in people with normal biotin status is much weaker than marketing suggests. The vitamin is recycled by the enzyme biotinidase, which releases biotin from older carboxylase enzymes for reuse. People with biotinidase deficiency cannot recycle biotin and require lifelong supplementation.

Evidence for 5 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Biotinidase deficiency

Grade A

Strong evidence

Lifelong supplementation (5-20 mg/day) is the standard treatment and reliably prevents neurological and dermatological complications in this rare inherited disorder. Identified through newborn screening in many countries.

Brittle nails

Grade C

Moderate evidence

Small uncontrolled studies suggest 2.5 mg/day for 3-6 months may improve nail thickness and reduce splitting in people with brittle nail syndrome. Effect is modest and the evidence base is thin.

Skin health (seborrheic dermatitis, cradle cap)

Grade C

Moderate evidence

Biotin has been used historically for seborrheic dermatitis in infants (cradle cap) with anecdotal benefit. Adult skin benefits in non-deficient individuals are not well-established.

Hair thinning (non-deficient adults)

Grade D

Mixed evidence

Despite massive marketing, controlled evidence that biotin improves hair growth or density in people with normal biotin status is weak. Improvement is more likely if someone has marginal biotin levels from anticonvulsants, malabsorption, or restrictive diets.

Multiple sclerosis (progressive)

Grade D

Mixed evidence

Early trials of very high-dose biotin (300 mg/day) in progressive MS were promising, but the larger SPI2 trial did not confirm benefit and the program was discontinued.

2 commercial forms

D-biotin

The natural, biologically active stereoisomer; well-absorbed.

Essentially all supplemental biotin is D-biotin. Standard tablets and capsules are inexpensive and effective.

Liposomal biotin

Marketed as enhanced absorption, but biotin is already well-absorbed.

Niche product. Likely does not meaningfully outperform standard D-biotin given biotin's high oral bioavailability.

Dosage

The Adequate Intake (AI) for adults is 30 mcg/day, with slightly more for lactating women. Most supplements contain 1,000-10,000 mcg (1-10 mg), far above what the body needs. Doses of 2.5-10 mg are commonly marketed for hair and nails. There is no UL. The DSLD shows biotin in nearly 20,000 supplement labels.

When and how to take it

Biotin is water-soluble and can be taken any time, with or without food. Most people take it in the morning along with a multivitamin or B-complex. Splitting doses is not required. Critically, stop biotin at least 72 hours before any planned blood work to avoid distorted lab results.

Food sources

Food	Amount	%DV
Beef liver (3 oz, cooked)	30.8 mcg	—
Eggs (1 large, whole, cooked)	10 mcg	—
Salmon (3 oz, cooked)	5 mcg	—
Pork chop (3 oz, cooked)	3.8 mcg	—
Sweet potato (1/2 cup, cooked)	2.4 mcg	—
Almonds (1/4 cup, roasted)	1.5 mcg	—
Sunflower seeds (1/4 cup)	2.6 mcg	—
Avocado (1 medium)	2-6 mcg	—

Safety

Biotin is among the safest vitamins, with no toxicity documented at oral doses up to 300 mg/day. The main safety concern is laboratory test interference: high-dose biotin distorts many common lab assays, including thyroid function, cardiac troponin (the heart attack marker), and various hormones. This has led to missed diagnoses. Stop biotin at least 72 hours before blood work.

Who should be cautious

People scheduled for blood tests should stop biotin at least 72 hours beforehand (longer for very high doses). Patients with biotinidase deficiency require lifelong dosing. Pregnant women have slightly higher needs. Generally safe across populations.

Interactions

Biotin can produce falsely abnormal results on immunoassays that use biotin-streptavidin chemistry, including thyroid panels, troponin, and hormone tests. Long-term anticonvulsants (phenytoin, carbamazepine, valproate) and prolonged antibiotic use can lower biotin status. Raw egg whites contain avidin, which binds biotin and prevents absorption when consumed regularly.

Frequently asked questions

Will biotin make my hair grow faster?⌄

If you are deficient, yes. If your biotin status is normal (true for nearly everyone eating a varied diet), the evidence that biotin improves hair growth is weak. Marketing far outpaces the science.

Why must I stop biotin before lab tests?⌄

High-dose biotin interferes with many common lab assays, producing falsely high or low values for thyroid hormones, troponin (a heart attack marker), and various hormones. This has led to missed diagnoses. Pause at least 72 hours before blood work.

Is biotin safe at high doses?⌄

Yes, in terms of direct toxicity. Doses up to 300 mg/day have been tested without harm. The main risk is lab test interference, not poisoning.

Do raw eggs really block biotin?⌄

Yes. Raw egg whites contain avidin, which binds biotin so tightly that biotin can't be absorbed. Cooking destroys avidin. Eating many raw eggs over time can cause deficiency.

Is biotin in my multivitamin enough?⌄

For preventing deficiency, almost certainly. Most multivitamins contain hundreds of micrograms — many times the AI of 30 mcg/day.

References

NIH Office of Dietary Supplements - Biotin Fact Sheet — NIH ODS link
FDA Safety Communication on Biotin Lab Interference — FDA link
Biotin - Wikidata — Wikidata link

Track Biotin with Pilora

Set up dose reminders, check interactions, and join the community in the Pilora iPhone app.

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Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.