Biotin (Vitamin H): What It Does, How Much You Need, Grey Hair and Blood Tests (UK)

What is vitamin H?

Vitamin H is an old name for biotin, now known as vitamin B7. The “H” is usually traced to the German words Haar and Haut, hair and skin, because early research linked a lack of it to hair loss and skin rashes. It is one of the 8 B vitamins, dissolves in water and isn’t stored in large amounts.

Most B vitamins have a set UK daily amount, but the NHS says the bacteria in your bowel make biotin, so it isn’t clear you need any extra from food. For the other 7, see our guide to B vitamins.

What does biotin do?

Biotin is a helper (coenzyme) for 5 enzymes that break down fats, carbohydrates and protein and build fatty acids. The NHS says the body needs it in very small amounts to make fatty acids. Great Britain’s nutrition and health claims register lists 7 authorised claims for biotin, worded exactly as below.

• Biotin contributes to normal energy-yielding metabolism.
• Biotin contributes to normal functioning of the nervous system.
• Biotin contributes to normal macronutrient metabolism.
• Biotin contributes to normal psychological function.
• Biotin contributes to the maintenance of normal hair.
• Biotin contributes to the maintenance of normal mucous membranes.
• Biotin contributes to the maintenance of normal skin.

A product can only use these claims if it contains at least a “source” amount of biotin, generally 15% of the NRV. Notice what isn’t on the list: hair growth, thicker hair, stronger nails or hair colour.

How much biotin do you need a day?

Adults need roughly 30 to 50 micrograms of biotin a day: EFSA sets an adequate intake of 40 micrograms and labels use an NRV of 50 micrograms. The NHS sets no UK figure, because gut bacteria make biotin and a varied diet provides plenty. It says 0.9mg (900 micrograms) or less a day from supplements is unlikely to cause harm.

EFSA hasn’t set an upper limit for biotin because there isn’t enough data on harm from high intakes. The known problem with high doses is the lab test issue below. Labels list biotin in micrograms (µg or mcg), so 10,000mcg is the same as 10mg. Check your multivitamin and any hair gummies together, and see can you overdose on vitamins? for the safe amounts of each nutrient.

Which foods are high in biotin?

The foods highest in biotin are liver, cooked eggs, salmon, pork, avocado, seeds and nuts. One large cooked egg gives about 13 to 25 micrograms, a third to half of the NRV, and a 3oz (85g) portion of cooked liver gives 27 to 35 micrograms. Most fruit, vegetables and dairy contain small amounts.

Figures are ranges from the Linus Pauling Institute, because biotin content varies a lot between samples. Cook your eggs: raw egg white contains avidin, a protein that binds biotin and stops you absorbing it, and cooking breaks avidin down.

Does biotin help grey hair?

There’s no good evidence that biotin, or vitamin H, prevents or reverses grey hair. Greying is mainly down to genes and age. One small 2017 study found slightly lower biotin levels in young people with early greying, but none of them was deficient. Biotin’s authorised hair claim covers normal hair, not hair colour.

• The colour claim belongs to copper: the only authorised GB claim about hair pigment is “copper contributes to normal hair pigmentation”. Most diets provide enough copper, and too much zinc can lower it; see our zinc guide.
• What the study found: 52 people under 20 with early greying in India had lower vitamin B12, folic acid and biotin than people without it. The biotin gap was small and every result was in the normal range, so the authors called for larger studies.
• What is linked to early greying: family history, smoking, low vitamin B12, thyroid and other autoimmune conditions, and vitiligo. A 2018 review says hair dye remains the main option for the look of grey hair, once any nutritional cause is treated.

iIf you’re going grey early and also feel tired, short of breath or have pins and needles, ask your GP about a blood test. See vitamin B12 deficiency symptoms, underactive thyroid symptoms and our guide to whether stress causes grey hair.

Does biotin help hair growth?

Biotin only helps hair in people who are short of it, which is rare. A 2017 review found 18 reported cases where biotin improved hair or nails, and every one had an underlying cause, such as biotin deficiency or a rare hair condition. The authors found no evidence that biotin helps hair growth in healthy people.

Hair shedding more often comes from iron deficiency, thyroid problems, a recent illness, stress or hormones. See why is my hair falling out?, stress and hair loss, and the best supplements for hair growth, which ranks each nutrient by evidence. For nails, the biotin evidence is a little stronger: see brittle nails.

Biotin deficiency: causes and signs

Biotin deficiency is rare in healthy adults eating a normal diet. It can happen with a rare inherited condition called biotinidase deficiency, after eating lots of raw egg white over a long time, with long-term use of some epilepsy medicines, and with long-term tube or drip feeding without biotin. Signs include thinning hair and a scaly red rash around the eyes, nose and mouth.

iIn adults, the Linus Pauling Institute lists low mood, tiredness, numbness and tingling, and poor coordination as later signs. These have many commoner causes, so don’t self-diagnose: a GP can check. See peripheral neuropathy and why am I always tired?

Biotin and blood tests

High-dose biotin can make some blood tests read falsely high or falsely low, because many lab tests use biotin in their chemistry. In May 2025 the MHRA said biotin may interfere with thyroid function tests and that the risk rises with higher doses. The US FDA has warned that biotin can give falsely low troponin results, the test used to diagnose heart attacks.

• The evidence: in a small 2017 study in JAMA, 6 healthy adults took 10mg of biotin a day for a week. 9 of 23 tests that use biotin chemistry gave misleading results, including thyroid tests.
• Which tests: thyroid tests, troponin, vitamin D and some other hormone tests, depending on the lab’s equipment.
• Tell the clinician and lab: mention any biotin, hair supplement or multivitamin before a blood test, and ask how long to stop beforehand. Never stop a prescribed medicine to do this.
• Thyroid results that don’t fit: some thyroid tests read falsely high and others falsely low, so results can look like an overactive thyroid. See overactive thyroid symptoms.

If you have chest pain, call 999. Tell the paramedics or A&E team if you take high-dose biotin.

Who should check before taking biotin?

iMost adults don’t need a biotin supplement. Check with your GP or pharmacist first if you take epilepsy medicines, are having blood tests, have a thyroid or heart condition, or are pregnant or breastfeeding. Children should only take biotin on a doctor’s advice.

• Epilepsy medicines: carbamazepine, phenytoin and primidone may lower biotin; your prescriber can advise if you need more.
• Pregnancy and breastfeeding: the NHS advises folic acid and vitamin D; ask your midwife or GP before adding anything else.
• Skin rashes: a new rash or patchy hair loss needs a GP, not a supplement. See dry skin.