Vitamin B7 (biotin)
A water-soluble vitamin involved in the metabolism of fat, carbohydrate and protein, popularised for the health of hair, skin and nails.
Biotin (vitamin B7 or B8 depending on the nomenclature, or vitamin H) is a cofactor for enzymes of energy metabolism (carboxylases). It is famous for its association with hair, nails and skin.
The original angle (the myth of “hair” supplements): biotin is sold in huge quantities to make hair grow and strengthen nails. The reality is more nuanced:
- Biotin helps only in cases of proven deficiency (rare). In a person with normal status, taking a supplement brings no proven benefit for hair or nails: it is a very profitable marketing myth
- Real deficiency (hair loss, brittle nails, rashes) occurs in specific cases: eating too many raw eggs (see below), certain medicines, rare genetic disorders, pregnancy
The raw egg paradox: a fascinating curiosity: raw egg white contains avidin, a protein that binds to biotin and blocks its absorption. Eating a lot of raw eggs (for example some bodybuilders, extreme diets) can therefore cause a biotin deficiency! Cooking denatures avidin and solves the problem, one more argument against eating raw eggs.
⚠️ Interference with blood tests: a crucial and little-known medical point: high-dose biotin supplementation skews many laboratory tests (thyroid, cardiac troponin, hormones and so on), which can lead to false diagnoses (false hyperthyroidism, a missed heart attack). You must tell the lab about any biotin you take before a blood test and stop taking it a few days beforehand. It is a real cause of medical errors.
Sources: egg yolk (cooked!), liver, nuts, seeds, pulses, salmon, avocado, mushrooms. The gut microbiota also produces some of it.