Vitamins · 3 min read ·

Biotin: no proof for hair, a risk of wrong test results

Biotin is sold mainly for hair, skin and nails. Studies in healthy people do not support this — and high doses can fool laboratory tests.

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In a nutshell

1What it does and how much you need

Biotin helps enzymes make fatty acids, break down some amino acids and produce glucose. A dietary deficiency is rare.1

EFSA recommendation 40 µg EFSA set the adequate intake at 40 µg a day for adults and pregnant women and 45 µg when breastfeeding. It is based on usual intakes in Europe (26–50 µg a day), at which no deficiency appears.1

EFSA has not set an upper level — the data are not sufficient.2

2Absorption and forms

EFSA recommendation almost 100% Free biotin is absorbed almost completely. How well protein-bound biotin in food is absorbed is not yet known.1
Weak evidence — a small study 6 people Biotin was fully absorbed even at high doses: in an experiment with 6 volunteers, as much was excreted in the urine after a large oral dose as after an intravenous one.3

In the EU, supplements may contain a single form, D-biotin.4

3Hair, nails and disease

Weak evidence — a review 18 cases A review of studies on biotin for hair and nails found only 18 reported cases of its use. According to the authors, evidence of an effect is very limited.5
Moderate evidence — a large randomised trial 642 people In a trial of 642 people with progressive multiple sclerosis, high-dose biotin (300 mg a day) did not improve disability or walking more than placebo. It also distorted laboratory tests.6

4Beware of blood tests

Weak evidence — a small study 9 of 23 Six healthy people took 10 mg of biotin a day for a week — a dose common in hair supplements. Of 23 tests that use biotin in the measurement, 9 gave wrong results — some falsely high, others falsely low. The tests measured thyroid and parathyroid hormones, a heart failure marker, vitamin D and more.7

So before a blood test, tell your doctor or the laboratory that you take biotin.6,7

What to take from this

Sources

Written on , based on studies available at that date. Newer research may change the conclusions.

  1. EFSA NDA Panel (2014). Scientific Opinion on Dietary Reference Values for biotin. EFSA Journal 12:3580. doi.org/10.2903/j.efsa.2014.3580
  2. EFSA (2025). Overview on Tolerable Upper Intake Levels as derived by the Scientific Committee on Food (SCF) and the EFSA Panel on Nutrition (version 11). efsa.europa.eu
  3. Zempleni J., Mock D. M. (1999). Bioavailability of biotin given orally to humans in pharmacologic doses. Am J Clin Nutr 69:504–508. doi.org/10.1093/ajcn/69.3.504
  4. Directive 2002/46/EC on food supplements, Annex II — forms of vitamins and minerals permitted in supplements (consolidated version 26 Nov 2025). eur-lex.europa.eu
  5. Patel D. P., Swink S. M., Castelo-Soccio L. (2017). A review of the use of biotin for hair loss. Skin Appendage Disord 3:166–169. doi.org/10.1159/000462981
  6. Cree B. A. C. et al. (2020). Safety and efficacy of MD1003 (high-dose biotin) in patients with progressive multiple sclerosis (SPI2): a randomised, double-blind, placebo-controlled, phase 3 trial. Lancet Neurol 19:988–997. doi.org/10.1016/S1474-4422(20)30347-1
  7. Li D. et al. (2017). Association of biotin ingestion with performance of hormone and nonhormone assays in healthy adults. JAMA 318:1150–1160. doi.org/10.1001/jama.2017.13705

This is general information and does not replace a doctor. Before blood tests, always say which supplements you take.