Vitamin B7

Biotin, also known as vitamin B7 or vitamin H, is an essential water-soluble B vitamin discovered in the early 20th century. It was initially called "bios" and later "vitamin H" (from the German "haut" meaning skin) due to its effects on skin health.

Biotin's primary function is as a cofactor for carboxylase enzymes, which are essential for metabolism of fatty acids, glucose, and amino acids. It also plays important roles in gene expression and cell signaling.

Despite its popularity as a beauty supplement for hair, skin, and nails, scientific evidence supporting these benefits in healthy individuals is limited. Biotin deficiency does cause hair loss and skin rashes, which likely explains the marketing claims. However, supplementation appears to benefit only those with actual deficiency or specific conditions like brittle nail syndrome.

True biotin deficiency is rare in healthy people because biotin is widely available in foods and synthesized by gut bacteria. However, certain populations are at risk: pregnant women, people with alcohol dependence, those with inflammatory bowel disease, and individuals taking certain medications (anticonvulsants, long-term antibiotics).

An important consideration is that high-dose biotin supplementation can interfere with laboratory tests, particularly thyroid and cardiac troponin assays. This has led the FDA to issue warnings about biotin's potential to cause false test results.

Biotin functions primarily as a cofactor (prosthetic group) for five carboxylase enzymes in mammals:

1. Acetyl-CoA Carboxylase (ACC): Catalyzes the conversion of acetyl-CoA to malonyl-CoA, the first committed step in fatty acid synthesis. Two isoforms exist: ACC1 (cytosolic, for fatty acid synthesis) and ACC2 (mitochondrial, regulates fatty acid oxidation).

2. Pyruvate Carboxylase: Converts pyruvate to oxaloacetate, a critical step in gluconeogenesis (making glucose from non-carbohydrate sources) and replenishing Krebs cycle intermediates.

3. Propionyl-CoA Carboxylase: Metabolizes propionyl-CoA (from odd-chain fatty acids and certain amino acids) to methylmalonyl-CoA, eventually entering the Krebs cycle as succinyl-CoA.

4. Methylcrotonyl-CoA Carboxylase: Involved in leucine (amino acid) metabolism. Deficiency causes accumulation of toxic metabolites.

5. Methylmalonyl-CoA Carboxylase: Converts methylmalonyl-CoA to succinyl-CoA, important for amino acid and fatty acid metabolism.

Beyond its enzymatic roles, biotin influences gene expression. It affects the expression of genes involved in glucose metabolism, immune function, and cell cycle regulation through biotinylation of histones (epigenetic modification).

Biotin also plays roles in cell signaling, immune function, and gene silencing. It may influence the expression of genes involved in hair and skin health, though the exact mechanisms for these effects are not fully understood.

Biotin is found in many foods, with liver, egg yolks, and nuts being particularly good sources. Gut bacteria also synthesize biotin that can be absorbed.

Biotin deficiency causes dermatitis, hair loss (alopecia), and neurological symptoms. Severe deficiency can be life-threatening.

AI (Adequate Intake): adults 30 mcg/day. No established RDA due to insufficient data. Requirements increase during pregnancy (35 mcg/day) and lactation (35 mcg/day).

Biotin supplements typically contain D-biotin, the naturally occurring active form. Most supplements provide far more than the AI.