Also known as: Biotin, Vitamin H, D-biotin, Coenzyme R
VitaminsGood evidence
The hair, skin and nails vitamin, sold at doses hundreds of times above requirement. Genuine shortfall is rare, and high-dose biotin causes a specific practical problem worth knowing about before any blood test.
Typical dose
30.0–5000.0 mcg per day
Any time; stop 2-3 days before any blood test
What it is
Biotin is a water-soluble vitamin found in eggs, liver, nuts, seeds, salmon and sweet potato. Gut bacteria also produce some, though how much of that is absorbed and used is unclear.
Requirement is tiny, around 40 micrograms daily. Supplements routinely supply 5,000 or 10,000 micrograms — more than a hundred times that. This gap is worth understanding before buying: the high doses exist because biotin is cheap and a big number looks impressive, not because anyone established that they work better.
Raw egg white contains avidin, which binds biotin tightly and blocks its absorption. Cooking destroys avidin, so this only matters to anyone eating substantial quantities of raw egg white.
How it works
Biotin acts as a cofactor for five carboxylase enzymes, which attach carbon dioxide to molecules as part of building fatty acids, breaking down certain amino acids, and generating glucose from non-carbohydrate sources.
Its association with hair and nails comes from its role in fatty acid synthesis, which matters to keratin-producing tissue. That is a plausible link rather than a demonstrated benefit at supplemental doses.
Biotin also has a role in gene expression, attaching to histone proteins that package DNA, though the significance of this is not well established.
What the evidence shows
Where biotin status is genuinely low, correcting it clearly improves hair and nail quality. That is not in dispute, and it is the origin of the whole category.
The problem is that low biotin status is uncommon, and evidence that supplementation improves hair or nails in people who are not short of it is weak. Most supporting studies are small, old, uncontrolled, or conducted in people with an identified shortfall.
The honest position is that biotin is a genuine remedy for a genuine but uncommon shortfall, sold at enormous doses to a very large number of people who do not have it. If your hair or nails are a concern, biotin is a reasonable thing to try, but expectations should be modest.
Dosing
Adequate intake is around 40 micrograms daily. Ordinary food covers it.
Supplements commonly supply 5,000-10,000 micrograms. There is no established benefit to these amounts over smaller ones, and no known toxicity either, so the main cost is the money.
One genuinely important practical point: high-dose biotin interferes with a wide range of laboratory blood tests, because many use biotin-based detection chemistry. It can produce falsely high or falsely low results depending on the test, which has led to real diagnostic errors. Stop biotin supplements at least two to three days before any blood test, and tell whoever takes the sample that you have been taking it.
At a glance
Common forms
D-biotin, Within hair, skin and nail formulas, Within B-complex, Within multivitamins
Half-life / duration
Water-soluble; excess cleared in urine, though blood test interference persists for days
Timing
Any time; stop 2-3 days before any blood test
Competition status
Permitted — not on the WADA Prohibited List
Category
Vitamins
Safety and side effects
Biotin is remarkably well tolerated. No tolerable upper intake level has been established, and even very large doses have not been associated with toxicity.
The meaningful risk is not to your health but to your test results. High-dose biotin distorts many laboratory blood tests, and because the person interpreting those results may not know you are taking it, this has caused genuine diagnostic confusion. This is the single most important thing to know about biotin supplements.
Always mention biotin use before any blood test, and stop taking it a few days beforehand.
Who should avoid it
Stop taking biotin at least two to three days before any blood test, and tell whoever takes the sample — high doses interfere with many laboratory tests and can produce misleading results. Speak to your doctor before use if you take regular medication or are under medical care.
This entry is provided for information only. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Consult a qualified healthcare professional before use if you are pregnant, breastfeeding, taking medication or under medical supervision.
