Vitamin B7 (Biotin)

What Is Vitamin B7 (Biotin)?

Biotin, also called vitamin B7 or vitamin H, is a water-soluble B vitamin that functions as a covalently bound coenzyme for five carboxylase enzymes. These enzymes catalyze carboxylation reactions — the addition of carbon dioxide to a substrate — central to fatty acid synthesis, gluconeogenesis, and amino acid catabolism.

An Adequate Intake (AI) rather than an RDA has been established: 30 mcg/day for adults. Lactating women have an AI of 35 mcg/day. Biotin is not currently included on the US Nutrition Facts panel because deficiency is rare.

Key Functions

• Fatty acid synthesis: Acetyl-CoA carboxylase (ACC1/ACC2) uses biotin to convert acetyl-CoA to malonyl-CoA, the first committed step in fatty acid synthesis.
• Gluconeogenesis: Pyruvate carboxylase converts pyruvate to oxaloacetate, a critical step in producing glucose from non-carbohydrate precursors.
• Amino acid catabolism: Propionyl-CoA carboxylase and 3-methylcrotonyl-CoA carboxylase are required for the breakdown of certain branched-chain amino acids.
• Gene expression: Biotin modifies histones, influencing chromatin structure and gene regulation.

Deficiency, Interactions, and Food Sources

Biotin deficiency is uncommon but can occur with chronic consumption of raw egg whites, which contain avidin — a protein that binds biotin with very high affinity and blocks its absorption. Symptoms include hair thinning, a scaly red rash around facial orifices, depression, and lethargy. Long-term anticonvulsant therapy can also impair biotin status.

Rich food sources include beef liver, cooked eggs (cooking denatures avidin), salmon, pork, sunflower seeds, and sweet potatoes. Gut bacteria also synthesize biotin, though the contribution to human requirements is uncertain.