Coenzyme for carboxylases in fat, carbohydrate and amino-acid metabolism.
Switzerland age 18–65: 40 µg/day.
Eggs, fish, meat, nuts, seeds, sweet potato and legumes.
Rare; can cause hair thinning, rash, brittle nails and neurological symptoms.
The reverse is not true: common hair or nail problems almost never automatically mean biotin deficiency.
Hair, skin and nails can be affected in genuine severe deficiency but are diagnostically unreliable on their own.
Large amounts of raw egg white, some anti-seizure medicines, parenteral nutrition and rare genetic disorders.
Check more common causes of hair/nail problems first; test only when suspicion is justified.
No proven hair or nail benefit without confirmed deficiency.
High doses interfere with important laboratory tests, including thyroid and troponin assays.