Biotin (B7): Beyond Hair and Nails

Biotin has been heavily marketed as a hair and nail supplement, but its actual biological roles are far more fundamental. It serves as a cofactor for carboxylase enzymes that are critical for fatty acid synthesis, gluconeogenesis, and amino acid metabolism.

What Biotin Actually Does

Biotin functions as a coenzyme for five carboxylase enzymes in humans. These enzymes are involved in fatty acid synthesis (acetyl-CoA carboxylase), energy production from amino acids (propionyl-CoA carboxylase and 3-methylcrotonyl-CoA carboxylase), gluconeogenesis (pyruvate carboxylase), and oxaloacetate formation. Without adequate biotin, these metabolic pathways are impaired.

The Hair and Nails Question

The evidence for biotin supplementation improving hair and nails in people who aren't biotin-deficient is actually quite thin. Most positive case reports involve individuals with pre-existing deficiency or specific genetic conditions (like biotinidase deficiency). For people with adequate biotin intake, megadose supplements are unlikely to produce dramatic changes in hair or nail growth.

Food Sources & Gut Production

Biotin is found in egg yolks, liver, almonds, sweet potatoes, and spinach. Interestingly, gut bacteria in the large intestine produce biotin, though the extent to which this bacterial biotin is absorbed and contributes to human requirements is still debated. Raw egg whites contain avidin, a protein that binds biotin and prevents absorption — cooking denatures avidin and eliminates this concern.

For more on how biotin fits into the larger B-vitamin picture, see The Complete B-Complex.

External resources: NIH — Biotin Fact Sheet