Vitamin B7 (Biotin)

What it does

Vitamin B7, or biotin, works as a coenzyme for a small but critical group of enzymes called carboxylases. These enzymes handle key steps in metabolism: making glucose when it is in short supply (gluconeogenesis), building and breaking down fatty acids, and processing certain amino acids. Through them biotin helps keep blood sugar and energy supply steady between meals.

Biotin is also involved in gene regulation and in the normal turnover of rapidly growing tissues, which is why it is often associated with the health of hair, skin and nails. While marketing frequently promotes biotin for hair and nail growth, the clear benefits are seen in people who are genuinely deficient rather than as a general booster for those already getting enough.

Deficiency is rare because biotin is widespread in foods such as eggs, liver, nuts, seeds and some vegetables, and because bacteria in the gut make some as well. Interestingly, raw egg white contains a protein (avidin) that binds biotin and blocks its absorption, so a diet very high in raw egg white can, over time, cause a shortfall — cooking the egg deactivates it.