Vitamin B7 (Biotin)

Biotin (vitamin B7, sometimes called vitamin H) is needed for the activity of several carboxylase enzymes that the body uses in fat, carbohydrate, and amino acid metabolism. Gut bacteria make some biotin in the bowel, although how much of that contributes to overall status is uncertain. Dietary biotin deficiency in healthy adults eating any mixed diet is essentially absent.

Values per 100g from USDA SR Legacy and McCance and Widdowson 7th edition; the site's food entries currently store macros only.

The UK has not set a strict Reference Nutrient Intake (RNI) for biotin. NHS reproduces SACN's safe-intake range and notes the gut-bacteria contribution.

Biotin deficiency is essentially unknown from a normal UK diet. It is occasionally seen in:

• People on long-term parenteral nutrition without added biotin.
• People with rare inherited disorders (biotinidase deficiency, multiple carboxylase deficiency).
• Excessive raw egg-white consumption (raw egg white contains avidin, which binds biotin; cooked egg white is not a problem).
• Long-term broad-spectrum antibiotic use, which can reduce gut bacterial production.

Signs of clinical biotin deficiency include hair thinning or loss, scaly red skin rash (especially around the eyes, nose, and mouth), and neurological symptoms.

Biotin has very low toxicity. The body excretes the excess in urine.

NHS supplement guidance: taking 0.9mg (900 micrograms) or less a day of biotin in supplements is unlikely to cause any harm.

Blood-test interference at high doses. Biotin at doses commonly sold for hair, skin, and nails (typically 5,000 to 10,000 micrograms, often labelled as 5 to 10mg, a day) interferes with many laboratory tests that use biotin-streptavidin chemistry. The clinically relevant ones include:

• Thyroid function tests (TSH, free T4 and T3)
• Troponin (used to diagnose heart attacks)
• Hormone tests (including hCG, the pregnancy hormone)
• Some tumour markers

UK labs and the MHRA ask patients to declare any biotin-containing supplements before blood is taken, particularly at the higher doses, and recommend stopping high-dose biotin for at least 48 hours (longer in some cases) before the test. Lower B-complex doses (around 30 to 50 micrograms) are not usually a problem.

Routine biotin supplementation is not needed for healthy UK adults. B-complex products typically include modest amounts (30 to 50 micrograms), well within safe range.

The standalone "hair, skin and nails" market uses doses of 5,000 to 10,000 micrograms a day. The evidence that this produces meaningful cosmetic effects in people without biotin deficiency is weak. The blood-test interference is real, and the supplement is worth pausing before scheduled blood work.

• The B-vitamin family: Vitamin B1, Vitamin B2, Vitamin B3, Vitamin B5, Vitamin B6, Folate, Vitamin B12.
• Best food sources: Eggs, Salmon, Sweet potato, Mushrooms.

• NHS. Vitamins and minerals: Vitamins B. nhs.uk/conditions/vitamins-and-minerals/vitamin-b.
• MHRA. Biotin (vitamin B7) interference with laboratory tests. Drug Safety Update, June 2019.
• SACN. Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. Department of Health Report 41 (1991).
• Public Health England. McCance and Widdowson's The Composition of Foods, 7th summary edition (2015).

This page is reference information for UK shoppers. It is not medical advice. Declare biotin supplements before blood tests.