Vitamin B7 / biotin

Biotin helps enzymes that process fats, carbohydrates and proteins. Most people get enough from food, and true deficiency is uncommon. It is sold in very high amounts for hair and nail growth, an area where evidence in people who are not deficient is thin, while the risk of distorting blood test results is real and documented.

Biotin is a small, water-soluble molecule. Raw egg white contains avidin, which binds biotin and blocks absorption; cooking prevents this.

Biotin is a cofactor for carboxylase enzymes involved in energy production from fats and carbohydrates and in amino-acid breakdown. It also has roles in gene regulation.

Supplementation clearly helps people with deficiency or biotinidase deficiency. For hair thickness or nail strength in people with normal status, the supporting studies are small, often uncontrolled, and frequently in people with an underlying deficiency or a specific brittle-nail condition, so they do not establish general benefit.

Cell and animal studies describe carboxylase function, biotin transport and effects of experimental depletion.

Evidence gap: Non-human evidence. It does not support cosmetic claims in people with adequate biotin.

Biotin is absorbed in the small intestine and excess is excreted in urine. The most important practical interaction is not with a medicine but with blood tests: high-dose biotin can make some results wrong in either direction.

Biotin itself has low toxicity and no established upper intake level, but 'non-toxic' is not the same as harmless. High-dose biotin has caused misdiagnosis through incorrect laboratory results, including missed heart attacks and mistaken thyroid diagnoses. Stop biotin before blood testing only on the advice of the requesting clinician, and always tell laboratory and emergency staff you take it. Anyone having thyroid, hormone or cardiac testing should disclose biotin use.

Tablets, capsules, gummies, multivitamins and hair-skin-nail blends are the common forms, frequently in very high amounts.

Biotin is relevant to nutrient adequacy and to specific deficiency states. For hair or nail concerns, evaluation of iron, thyroid function, protein intake, medication effects, scalp conditions and hormonal causes is more likely to identify a treatable explanation than supplementation is.

Educational example: a person taking a high-dose hair supplement attends hospital with chest pain, and the troponin result reads falsely low. The decision factors are disclosure of supplement use, the assay platform used, and whether the clinical picture matches the numbers. Questions worth asking: does this amount of biotin affect my upcoming tests, and should the laboratory be told? Hair-growth marketing rarely mentions test interference, which is the best-documented risk of high-dose biotin.