Biotin is a water-soluble B vitamin — also known as vitamin B7 or, historically, vitamin H (from the German Haar und Haut, "hair and skin"). It functions primarily as a coenzyme for five carboxylase enzymes that are essential for:
- Fatty acid synthesis — biotin-dependent acetyl-CoA carboxylase is required for de novo lipogenesis
- Gluconeogenesis — pyruvate carboxylase, a biotin-dependent enzyme, is a critical step in glucose production from non-carbohydrate sources
- Amino acid catabolism — propionyl-CoA carboxylase is involved in branched-chain amino acid metabolism
- Cell signalling — biotin affects gene expression, including the transcription of several metabolic genes
How Much Biotin Do You Need?
The UK Reference Nutrient Intake (RNI) is not formally established for biotin — the UK sets an "adequate intake" of around 30–35 mcg/day for adults. The US AI is 30 mcg/day. These values are modest and achievable through a normal mixed diet.
A standard Western diet provides approximately 35–70 mcg/day of biotin. True deficiency is rare in healthy adults eating varied diets.
Biotin Deficiency: When Does It Occur?
Biotin deficiency, when it does occur, causes:
- Hair thinning and loss
- Brittle nails
- Scaly, red rash around the nose, eyes, and mouth
- Neurological symptoms in severe cases (lethargy, hallucinations, paraesthesia)
- In infants: hypotonia (low muscle tone), developmental delay
Risk factors for deficiency:
- Biotinidase deficiency — a rare inherited disorder preventing biotin recycling
- Prolonged raw egg white consumption — egg white contains avidin, a protein that binds biotin and prevents its absorption. Cooking denatures avidin. This is an unusual cause of deficiency but biomedically established.
- Long-term anticonvulsant use — certain epilepsy medications (phenytoin, carbamazepine) reduce biotin absorption
- Parenteral nutrition without biotin supplementation
- Chronic alcoholism — impairs absorption
- Pregnancy — biotin catabolism increases; subclinical deficiency is relatively common
Food Sources of Biotin
Biotin is widespread in food, though content varies significantly:
| Food | Biotin Content (approx.) |
|---|---|
| Cooked beef liver (85g) | 31 mcg |
| Cooked egg (1 whole) | 10 mcg |
| Salmon (85g cooked) | 5 mcg |
| Pork (85g) | 4 mcg |
| Sunflower seeds (30g) | 2.6 mcg |
| Sweet potato (125g cooked) | 2.4 mcg |
| Almonds (30g) | 1.5 mcg |
| Tuna (85g canned) | 0.6 mcg |
Biotin is also produced by gut bacteria, though the extent to which this contributes to human biotin status is debated.
The Hair and Nail Supplement Claim
Biotin supplements are heavily marketed for hair growth, nail strength, and skin health. This is the primary reason most people take it.
What the evidence shows:
In people with genuine biotin deficiency — which does cause hair loss — correcting the deficiency improves hair growth. This is uncontroversial.
In people who are not biotin-deficient, the evidence for benefit is much weaker:
- Most clinical trials are small and lack control groups
- A 2017 review in Skin Appendage Disorders found that the majority of studies reporting improvement were either uncontrolled, very small, or conducted in patients with underlying deficiency or rare genetic conditions
- No large, rigorous RCT has demonstrated meaningful hair or nail benefit in non-deficient individuals
The US FDA issued a safety communication in 2017 noting that high-dose biotin supplements (common in hair/nail supplements) can significantly interfere with certain laboratory tests — including cardiac troponin tests (used to diagnose heart attacks) and thyroid hormone tests — potentially causing falsely low or falsely high results. This is a genuine clinical concern, not theoretical.
Doses in supplements: Many commercially available biotin supplements contain 5,000–10,000 mcg (5–10 mg) — 150–300× the adequate intake. There is no established tolerable upper intake level for biotin because no adverse effects from high doses have been documented, but the laboratory interference issue is a practical concern at these doses.
Biotin and Pregnancy
Subclinical biotin deficiency may be common in pregnancy — estimates suggest up to 50% of pregnant women have marginal biotin status due to increased catabolism. There is emerging animal evidence that even subclinical deficiency may affect embryonic development, though robust human data is limited.
Most prenatal vitamins contain biotin. Pregnant women should not avoid biotin supplementation from fear of causing harm — the concern is deficiency, not excess.
Key Takeaways
Biotin is an essential coenzyme for several fundamental metabolic pathways. Deficiency is uncommon in healthy adults but does cause hair loss and other symptoms. The claim that supplementing biotin improves hair or nail quality in non-deficient people is not well-supported. High-dose biotin supplements can interfere with important blood tests.
For context on how biotin fits into your overall vitamin intake, see what vitamins should I take daily.
Frequently Asked Questions
Does biotin cause acne? Some people report acne breakouts with high-dose biotin supplementation. The proposed mechanism: high-dose biotin competes with pantothenic acid (B5) for intestinal absorption, and B5 deficiency is associated with acne. This is plausible but not confirmed in clinical trials.
How long does biotin take to work? In people with genuine deficiency, improvement in hair shedding and nail brittleness can be seen within 1–3 months. In non-deficient people taking supplements, there is no reliable timeframe because the benefit is not well-established.
Is biotin safe? No upper tolerable limit has been set, and toxicity has not been reported. The main practical concern is laboratory test interference at high doses. If you're taking high-dose biotin and having blood tests done, inform your doctor.
Who genuinely needs a biotin supplement? People with biotinidase deficiency (a genetic condition requiring medical supervision), those on long-term anticonvulsants, those who regularly consume raw egg white, or those with confirmed deficiency. Otherwise, diet covers requirements for most people.
Does cooking destroy biotin? Biotin is relatively stable to heat. Cooking reduces raw egg white's avidin content, which actually increases net biotin absorption from eggs — the opposite of what you'd expect.
Sources & References
- Mock DM. "Biotin." In: Modern Nutrition in Health and Disease, 11th ed. Wolters Kluwer, 2014.
- Patel DP, Swink SM, Castelo-Soccio L. "A review of the use of biotin for hair loss." Skin Appendage Disorders, 2017.
- US FDA Safety Communication. "The FDA warns that biotin may interfere with lab tests." 2017, updated 2019.
- National Institutes of Health Office of Dietary Supplements. "Biotin Fact Sheet for Health Professionals." 2023.
- Zempleni J, et al. "Biotin and biotinidase deficiency." Expert Review of Endocrinology & Metabolism, 2008.