Vitamin B7 (biotin)

vitaminvitamin B7

What is it

Vitamin B7, commonly called biotin, is a water-soluble B-vitamin that serves as a coenzyme for five essential carboxylase enzymes involved in glucose, fatty acid, and amino acid metabolism. It is best known for its popular reputation in supporting hair, skin, and nails.

How it works

Biotin is absorbed in the small intestine and circulates bound to proteins. Inside cells, the enzyme holocarboxylase synthetase attaches biotin to four mitochondrial carboxylases (pyruvate carboxylase, propionyl-CoA carboxylase, methylcrotonyl-CoA carboxylase, acetyl-CoA carboxylase 2) and one cytosolic carboxylase (acetyl-CoA carboxylase 1). These enzymes are essential for gluconeogenesis, amino acid catabolism, and fatty acid synthesis. Biotin also plays a role in gene expression by modifying histones, though the physiological significance of this is still being studied. Gut bacteria synthesize some biotin, contributing modestly to total body stores.

Evidence for 5 uses

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

Biotinidase deficiency / inherited biotin metabolism disorders

Grade A

Strong evidence

Lifelong biotin supplementation (5-20 mg/day) is the standard treatment and effectively prevents neurological damage and skin/hair manifestations in this rare inherited condition.

Brittle nails

Grade C

Moderate evidence

Small studies suggest 2.5 mg/day for several months may improve nail thickness and reduce brittleness, particularly in those with poor baseline status. Effect size is modest and evidence quality is limited.

Hair growth (without diagnosed deficiency)

Grade D

Mixed evidence

Despite widespread marketing, evidence that biotin improves hair growth or thickness in people without deficiency is weak and inconsistent. People with adequate biotin status are unlikely to benefit.

Diabetic neuropathy

Grade D

Mixed evidence

A few small studies tested very high biotin doses for diabetic neuropathy with mixed results. Not part of standard care.

Multiple sclerosis (progressive)

Grade D

Mixed evidence

Initial trials of very high-dose biotin (300 mg/day) in progressive MS showed promise but the larger SPI2 trial was negative. Not currently recommended.

1 commercial form

D-biotin

The natural and biologically active form; only D-biotin is used by enzymes.

Essentially all supplemental biotin is D-biotin. Well absorbed in standard capsule and tablet forms.

Dosage

The Adequate Intake (AI) for adults is 30 mcg/day, with 35 mcg for lactating women. Most supplements contain 1,000-10,000 mcg (1-10 mg), far above physiological needs. Doses of 5-10 mg/day are commonly marketed for hair and nail support. There is no established UL because biotin shows no toxicity at high doses.

When and how to take it

Biotin is water-soluble and can be taken at any time of day, with or without food. It is often included in morning B-complex formulas. If you take a multivitamin separately, there is no benefit to special timing. Stop high-dose biotin at least 72 hours (some labs recommend longer) before any blood tests to avoid assay interference.

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	—
Sunflower seeds (1/4 cup)	2.6 mcg	—
Almonds (1/4 cup, roasted)	1.5 mcg	—
Sweet potato (1/2 cup, cooked)	2.4 mcg	—
Tuna (3 oz, canned)	0.6 mcg	—

Safety

Biotin is considered very safe with no documented toxicity at oral doses up to 300 mg/day. The most important safety issue is laboratory test interference: high-dose biotin can cause falsely high or low results on many common assays (thyroid hormones, troponin, vitamin D, hormones), which has led to misdiagnoses including missed heart attacks. Stop biotin at least 72 hours before blood work.

Who should be cautious

Pregnant women may have higher needs and modestly reduced status. People with biotinidase deficiency require lifelong biotin supplementation. Patients scheduled for blood work should pause biotin 72+ hours beforehand. Otherwise generally safe across populations.

Interactions

Biotin's main clinical issue is interference with immunoassay laboratory tests using biotin-streptavidin chemistry. This can produce false thyroid function results, troponin readings, and hormone levels. Anticonvulsants (carbamazepine, phenytoin, valproate) and long-term antibiotics may lower biotin status. Raw egg whites contain avidin, which binds biotin and prevents absorption.

Frequently asked questions

Will biotin actually grow my hair?⌄

If you have biotin deficiency, yes. If your levels are normal (true for almost everyone with a balanced diet), evidence that supplemental biotin grows hair is weak.

Why do I need to stop biotin before blood tests?⌄

High-dose biotin interferes with the chemistry used in many lab assays, producing falsely high or low results for thyroid hormones, troponin (heart attack marker), vitamin D, and hormones. This has led to misdiagnoses. Stop at least 72 hours before blood work.

How much biotin is too much?⌄

There is no established upper limit. Doses up to 300 mg/day have been tested without toxicity. The main risk is lab test interference, not direct harm.

Can raw eggs cause biotin deficiency?⌄

Yes, in theory. Raw egg whites contain avidin, which binds biotin and prevents absorption. Cooking destroys avidin. Eating many raw eggs daily over time can cause deficiency.

Should I take biotin with other B vitamins?⌄

B vitamins work together in energy metabolism, so a B-complex is a reasonable approach if you want B-vitamin support. Standalone high-dose biotin is unnecessary for most people.

References

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

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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.