Biotin (Vitamin B7)

What it is

Biotin is a water-soluble vitamin from the B group. The D-A-CH nutrition societies estimate the requirement of adults at 40 µg per day, for breastfeeding women at 45 µg; EFSA arrives at the same values. According to the German National Nutrition Survey, men in Germany take in a median of 43 to 48 µg, women 39 to 42 µg. Most people are therefore well supplied through food.

Good sources are liver, eggs, fish, nuts and seeds. A boiled egg provides about 10 µg. Hair and nail preparations, by contrast, often contain milligram amounts. The US Food and Drug Administration (FDA) cites products with up to 650 times the recommended daily amount.

How it works

Biotin sits as a cofactor in several carboxylases. These enzymes build fatty acids, break down certain amino acids and help with gluconeogenesis. If biotin is lacking, these pathways stall. This shows up first in fast-growing tissue, that is, in skin, hair and nails, and later also in the nervous system.

This explains its reputation as a beauty vitamin. But the logic applies in one direction: anyone who has too little benefits. Whether additional biotin produces more hair or stronger nails when supply is already full is another question, and so far the data do not answer it positively.

When a deficiency occurs

A classic deficiency is rare, but not exotic. Congenital biotinidase deficiency affects about 1 in 25,000 newborns and is part of newborn screening in Germany. Detected early and treated with biotin, these children have an excellent prognosis.

Acquired deficiencies arise from heavy alcohol use, smoking, long-term antibiotic or antiepileptic therapy and from raw eggs, whose egg-white protein avidin binds biotin. In pregnancy, according to the NIH, at least one third of women develop a mild deficiency. In a Zurich hair clinic, 38 percent of 541 women with hair loss had biotin levels in the deficient range.

What the studies show

Hair loss and biotin levels

Ralph Trüeb evaluated 541 women who came to his Zurich practice in 2014 because of hair loss and whose biotin levels were measured. 38 percent were below 100 ng/L and thus in the deficient range, 13 percent in the optimal range. Only 11 percent of the women with a deficiency had known risk factors. His conclusion: give biotin selectively after measurement, not across the board. The study is retrospective and has no treatment arm.

High dose in multiple sclerosis

In the first study, 154 patients with progressive MS received 100 mg of pharmaceutical biotin three times daily or placebo. 12.6 percent on biotin improved, nobody on placebo. The large follow-up study SPI2 with 642 patients in 13 countries did not confirm this: 12 versus 9 percent, statistically no difference. The manufacturer had already withdrawn the marketing authorization application in the EU in 2017. This is study information only, not a treatment option.

Lab values after 10 mg biotin

Six healthy adults took 10 mg biotin daily for one week, a typical dose in hair preparations. Afterwards, 37 lab tests were checked. Of 23 tests that work on the biotin-streptavidin principle, 9 gave false values, of the 14 others none. Depending on the test design, the results came out falsely high or falsely low.

Where the data stop

For the main promise, more and stronger hair in people without a deficiency, proof is lacking. A 2024 review found only three studies on oral biotin and hair growth. The best of them, double-blind and placebo-controlled, saw no difference from placebo. In a small randomized study with 10 healthy men, 5 mg biotin over 14 days did not change the growth rate. Only in combination with minoxidil did it increase, and that is a medicine. The nail studies date from 1989 to 1993, were uncontrolled or retrospective and in part subjectively assessed. There is no modern placebo-controlled nail study. The authorized EU health claim on the maintenance of normal hair sounds strong, but is based on the role in preventing deficiency. According to the German consumer advice center (Verbraucherzentrale), EFSA emphasizes that the population is adequately supplied and that additional biotin has no further effect on skin and hair. For nails there is no authorized claim at all. In multiple sclerosis, the high dose is off the table after the negative phase 3 study.

Status, approval and legal

Biotin is an authorized vitamin for food supplements and is also on the market as a medicine. Because there is no known toxicity, neither the EU nor the US has set a tolerable upper intake level, and the BfR has refrained from setting a maximum amount since 2016. Instead, it recommends a note on every biotin-containing preparation that physicians or the laboratory should be informed before lab tests. For medicines with at least 150 µg per dose, this warning has been mandatory since a Dear Doctor letter (Rote-Hand-Brief) in 2019. Authorized health claims include energy metabolism, the nervous system, skin, hair and mucous membranes. Biotin is not on any doping list.

Safety

Biotin itself is remarkably safe. The NIH reports patients who took up to 200 mg daily without signs of toxicity. The real risk lies in the laboratory. Many tests use the strong binding of biotin to streptavidin, and too much biotin in the blood confuses them. Thyroid values can then mimic Graves’ disease, as a case from Düsseldorf University Hospital showed. Troponin, the central marker for heart attack, can come out falsely low. The FDA issued warnings in 2017 and again in 2019 and reported one death. The EMA sees a possible risk from 150 µg daily. After 5 mg, the interference lasted 8 hours in one study, after 10 mg 1 to 2 days. In everyday clinical practice this is rare: among 572 acute patients in Maastricht, not a single troponin value was disturbed. Caution applies especially in impaired kidney function, in children and in pregnancy, because biotin then stays in the blood longer or has a more sensitive effect. Antiepileptics can lower biotin levels.

Sources

• BfR, proposed maximum levels for biotin in foods including food supplements, 2021
• NIH Office of Dietary Supplements, Biotin Fact Sheet for Health Professionals
• Li et al., Association of biotin ingestion with performance of hormone and nonhormone assays in healthy adults, JAMA 2017
• Trüeb, Serum biotin levels in women complaining of hair loss, International Journal of Trichology 2016
• Patel et al., A review of the use of biotin for hair loss, Skin Appendage Disorders 2017
• Yelich et al., Biotin for hair loss: teasing out the evidence, Journal of Clinical and Aesthetic Dermatology 2024
• Floersheim, treatment of brittle fingernails with biotin, Zeitschrift für Hautkrankheiten 1989
• Cree et al., Safety and efficacy of MD1003 (high-dose biotin) in progressive multiple sclerosis (SPI2), Lancet Neurology 2020
• Zhang et al., Assessment of biotin interference in thyroid function tests, Medicine 2020
• FDA, Biotin Interference with Troponin Lab Tests – Assays Subject to Biotin Interference