Biotin

Biotin, also known as Vitamin B7 or Vitamin H, is a water-soluble B-vitamin that plays a central role in the metabolism of fats, carbohydrates, and proteins. It serves as a cofactor for five carboxylase enzymes — including pyruvate carboxylase (crucial for gluconeogenesis) and acetyl-CoA carboxylase (crucial for fatty acid synthesis). Biotin is found in foods like eggs (especially yolks), organ meats, nuts, and certain vegetables, but it is also synthesized by gut bacteria.

Biotin is most famous in the supplement world for its purported benefits for hair, skin, and nails. This reputation stems from case reports of biotin deficiency causing alopecia (hair loss), dermatitis, and brittle nails, and from the logical inference that correcting deficiency would reverse these symptoms. In clinical practice, biotin is routinely used for children with rare biotinidase deficiency, where it is genuinely life-saving. However, the evidence for high-dose biotin supplementation in people without deficiency is considerably more modest.

Despite the limited evidence for cosmetic applications, biotin is one of the most widely sold supplements, often marketed in mega-doses of 5,000–10,000 mcg. The daily adequate intake is only 30 mcg. One important safety consideration: high-dose biotin can cause clinically significant interference with biotin-based laboratory immunoassays — potentially producing false high or low results for thyroid hormones, troponin, PSA, and other critical tests. Many major health systems now advise stopping high-dose biotin at least 48–72 hours before blood tests.