Biotin (vitamin B7)

What it is

Biotin (vitamin B7) is a water-soluble B vitamin found in eggs, nuts, seeds, salmon, and organ meats. Gut bacteria make some too. Deficiency is rare in healthy people.

It is heavily marketed for hair, skin and nails, often in doses thousands of times higher than daily need. Raw egg white contains avidin, which binds biotin; eating a lot of raw egg white can cause deficiency.

The most important practical issue is that high-dose biotin can interfere with many lab tests, which has led to missed or wrong diagnoses.

How it works

Biotin is a coenzyme for enzymes that process fats, carbohydrates and amino acids. Lab tests using biotin-streptavidin chemistry can be thrown off by excess biotin in a blood sample.

What the evidence says

• Strong Correcting biotin deficiency
  Improves hair loss, rash and brittle nails when deficiency is the cause.
• Limited Brittle nails
  Small, older studies suggest modest nail thickening; quality of evidence is low.
• Weak Hair growth in people without deficiency
  No good evidence that extra biotin grows hair in healthy people.
• Strong Biotinidase deficiency and certain metabolic conditions
  Medically supervised use in rare disorders.
• Limited Multiple sclerosis (high-dose, investigational)
  Results are mixed and this is medical-supervision territory only.

Evidence ratings are our plain-English summary of how much good human research exists, not a promise of results. How we rate evidence.

Dosage and timing

• NHS advice is that taking 0.9 mg or less a day is unlikely to cause harm; many supplements exceed this, so check current guidance.
• Typical hair and nail products give 2,500 to 10,000 micrograms (2.5 to 10 mg), far above need.
• If you are due a blood test, tell the person ordering it that you take biotin.
• Stop high-dose biotin for several days before blood tests; many labs suggest at least 2 days, and some longer, so check with your clinician.

Forms and what to look for

• Biotin (D-biotin) is the only form; the label may say vitamin B7.
• Multi-ingredient hair formulas often include biotin plus zinc, selenium and others.
• Gummies may contain sugar and variable amounts.
• Some B-complex and multivitamin products contain biotin too, so you can double up without realising.

What to expect, and when

• Hair and nail growth is slow, so any change would need three to six months.
• Many people see no difference.
• Interference with lab tests can start within hours of a high dose.

Side effects

• Usually well tolerated.
• Nausea, stomach cramps or diarrhoea in some.
• Skin breakouts or acne in some people.
• Rarely, allergic reactions.

Interactions

• Lab test interference: troponin (heart attack test), thyroid function tests, hormone tests, vitamin D and others may read falsely high or low.
• Some anti-seizure medicines (carbamazepine, phenytoin) and long antibiotic courses can lower biotin.
• Taken with high-dose B5 (pantothenic acid), absorption may compete.
• Always tell any doctor or lab that you take biotin.

Who should avoid it

• Anyone who may need urgent blood tests (such as for chest pain) should tell clinicians if they take biotin.
• People with thyroid conditions being monitored should be especially careful.
• People starting a medical work-up or on hormone treatment should check first.
• Pregnant women should stick to NHS-recommended doses.

Risks and safety

• The US FDA has issued a safety warning about biotin interfering with lab tests, including troponin; UK clinicians raise the same concern.
• Wrong results can lead to missed diagnoses or wrong treatment.
• Not banned in sport.
• Doses on labels are often 30 to 60 times the daily need.

Buying well: quality and testing

• Check the dose in micrograms; 1 mg equals 1,000 micrograms, a common source of confusion.
• Third-party seals (NSF, USP) add confidence.
• Be wary of "hair growth" blends with vague claims.
• Lower doses (under 1 mg) cause less test interference trouble.

Bottom line

Biotin is a fine idea if you are truly deficient, but for most people it is an expensive gamble on hair and nails with a real downside: it can make blood tests unreliable. If you do take it, use a low dose and stop it before any tests.