What biotin does
Vitamin B7 helps enzymes that metabolise fats, carbohydrates and amino acids, and plays a role in gene regulation.
How much
Adults need about 30–40 µg a day.
Plant sources
Nuts and seeds (especially almonds and sunflower seeds), legumes and peanuts, sweet potatoes, mushrooms, oats and bananas. Gut bacteria make some biotin too.
A note
Biotin is popular in hair and nail supplements, but evidence for healthy people is weak. High-dose biotin can interfere with blood tests — including thyroid and heart tests — so tell your doctor if you take it.