B7

Biotin, also known as vitamin B7 or sometimes vitamin H, is a water-soluble B-complex vitamin that is essential for human metabolism. In humans, biotin serves as a coenzyme for carboxylase enzymes, including acetyl-CoA carboxylase, pyruvate carboxylase, propionyl-CoA carboxylase, and methylcrotonyl-CoA carboxylase. These enzymes participate in fatty acid synthesis, gluconeogenesis, and the breakdown of certain amino acids and odd-chain fatty acids.

Biotin can be obtained from the diet and is also synthesized by intestinal bacteria. Common dietary sources include egg yolks, liver and other organ meats, nuts, seeds, fish, dairy products, whole grains, and mushrooms. Raw egg whites contain avidin, a protein that binds biotin and reduces its absorption; cooking destroys avidin and improves bioavailability.

Absorption occurs in the small intestine; biotin circulates in the bloodstream largely bound to albumin and is excreted in urine. Deficiency is uncommon in healthy individuals but can occur with malabsorption, long-term use of certain anticonvulsants, copper overload, or genetic conditions such as biotinidase deficiency. Clinical signs of deficiency include thinning hair, dermatitis around the eyes, nose, and mouth, mood or cognitive changes, lethargy, and, in infants, hypotonia and seizures.

The recommended intake for adults is about 30 micrograms per day; pregnant individuals are about the same, and lactation requires around 35 micrograms. Biotin intake from supplements is generally safe for most people; there is no established upper intake level, but very high doses may interfere with certain laboratory tests and produce misleading results. Beyond deficiency treatment, biotin is sometimes marketed for hair and nail growth, though evidence in people without deficiency is limited.