Biotin is vitamin B7, a water-soluble B vitamin (older labels call it vitamin H). Its job is narrow: it sits inside a handful of enzymes called carboxylases that help your body build fatty acids, make glucose and break down certain amino acids. Adults need about 30mcg a day, and most diets already supply it.
That last part is the bit the beauty aisle would rather you skipped. Biotin is one of the most heavily marketed vitamins on the shelf and one of the least likely to be missing from your plate.
The short version
- Biotin is vitamin B7, a coenzyme for carboxylase enzymes.
- It helps make fatty acids and glucose, per a 2019 review.
- Adults need about 30mcg a day. Western diets supply 35 to 70mcg.
- Pregnancy and some anti-seizure drugs raise biotin needs.
- A 10mg daily dose skewed 9 of 23 lab tests in a small trial.
What biotin actually does in your body
Most vitamins get described as if they "support energy". Biotin has a more specific CV than that. It acts as a prosthetic group, a permanent attachment, on enzymes known as biotin-dependent carboxylases. According to a 2019 review in the Journal of Inherited Metabolic Disease, those enzymes run key steps in gluconeogenesis (making new glucose), fatty acid synthesis and amino acid breakdown. Biotin's role is mechanical. It carries a carboxyl group from one molecule to another, then goes back for the next one.
Two of those enzymes matter for how scientists measure biotin status. Propionyl-CoA carboxylase and methylcrotonyl-CoA carboxylase both slow down when biotin runs short, and when the second one slows, a by-product called 3-hydroxyisovaleric acid builds up in urine. Researchers use that by-product as a readout of marginal deficiency, as described in Zempleni and Mock's 1999 review of human biotin requirements. Keep that acid in mind. It shows up again in the pregnancy data below.
The 2019 review also covers the other proposed role that gets more attention lately: biotin regulating gene expression, separate from its job in the carboxylases. It describes the related work on neurological disease as a developing literature. Translation: interesting, not settled, and not a reason to buy anything.
How much biotin you need, and where it comes from
The adequate intake for adults is 30mcg a day, the figure the US uses and the one the NIH Office of Dietary Supplements lists. The same 1999 review estimated typical Western intake at 35 to 70mcg a day and found that humans absorb biotin nearly completely. So the average plate clears the bar before you count anything else.
Food sources are spread thin. The NHS describes biotin as present in a wide range of foods, but only at very low levels. Cooked eggs, liver, salmon, nuts and seeds are the usual entries on the NIH food list. No single food carries the day. You get it the boring way, a little from everything.
There is a second supplier that no food label accounts for: your gut. The NHS notes that the bacteria in your bowel can make biotin, and says it is not clear whether you need any extra from food at all. A 2011 review of water-soluble vitamin absorption in the Biochemical Journal backs up the plumbing side of that: the large intestine has dedicated uptake systems for vitamins made by gut microflora. How much this contributes to your overall biotin status is still an open question.
Who actually runs low on biotin
Frank, symptomatic biotin deficiency is rare, according to a 2017 review by Donald Mock in the Journal of Nutrition. Marginal deficiency is a different story, and it clusters in specific groups rather than spreading evenly across everyone.
| Situation | What the research found |
|---|---|
| Eating raw egg white | 10 healthy adults eating undenatured egg white for 28 days developed marginal biotin deficiency, reversed after repletion. |
| Pregnancy | About 50% of pregnant women showed raised 3-hydroxyisovaleric acid. 300mcg of biotin a day for 14 days brought it down. |
| Long-term anti-seizure medication | Adults on long-term anticonvulsants broke biotin down faster and probably had reduced biotin status. |
| Chronic alcohol use, gut disease or resection | These interfere with water-soluble vitamin absorption, biotin included. |
| Biotinidase deficiency | An inherited condition, often found by newborn screening, that responds to oral biotin treatment. |
The raw egg detail is the one worth knowing if you train. Raw egg white contains a protein called avidin that binds biotin and blocks its absorption, per the NIH biotin fact sheet. Cooking denatures avidin, which is why the researchers in that 28-day study had to use undenatured egg white to cause the deficiency in the first place. If your breakfast is six raw whites in a shaker, that is the one habit on this list you control. Cook them.
Notice who is missing from the table. A healthy man eating a mixed diet with cooked eggs is not on it.
Why the label says 10,000mcg
Walk down any supplement aisle and you will find biotin sold in 5,000mcg and 10,000mcg doses. Against a 30mcg adequate intake, 10,000mcg is about 333 times what you need (10,000 divided by the 30mcg adequate intake). The pitch is almost always hair and nails.
The evidence for that pitch is thin. A 2017 review in Skin Appendage Disorders found 18 reported cases of biotin helping hair or nails, and every single one involved an underlying condition behind the poor growth. The authors concluded there was not enough evidence to support supplementing healthy people. We covered the hair question on its own in does biotin help hair growth, so the short answer here: only if you were deficient to begin with.
Megadoses also have a cost that has nothing to do with hair. Many hospital blood tests use biotin and streptavidin as part of the chemistry. In a 2017 JAMA trial, 6 healthy adults took 10mg of biotin a day for a week. Interference showed up in 9 of the 23 biotin-based assays tested, with some results reading falsely high and others falsely low. Six people is a small study. It was still enough for the authors to say doctors should ask about biotin before ordering bloods.
Even the most ambitious use of high-dose biotin has stalled. The SPI2 trial in the Lancet Neurology gave 642 patients with progressive multiple sclerosis 100mg of pharmaceutical biotin three times a day, or placebo. After 12 months, 12% improved on biotin against 9% on placebo, a difference that did not reach significance, and the authors concluded it could not be recommended. That is 300mg a day, ten thousand times the 30mcg adequate intake, and it still did not move the result. That trial was never about supplements, but it does show how little the extra milligrams buy.
So what should you do about biotin?
For most men, very little. Eat a mixed diet, cook your eggs, and you are probably already above 30mcg before your gut bacteria add their share. The UK Department of Health and Social Care advice, as set out on the NHS vitamin B page, is that a varied, balanced diet should give you all the biotin you need.
If you are on long-term anti-seizure medication, drink heavily, or have a gut condition affecting absorption, that is a conversation for your GP, who can look at your whole picture rather than one vitamin. And if you are about to have blood work while taking a high-dose biotin product, tell whoever is ordering the test. The JAMA authors made exactly that point.
Biotin is a real vitamin with a real job. It is just a small job, done at a small dose, and most of the time it is already done.
We sell a daily formula, so take this with that in mind. Fireblood includes 120mcg of biotin as D-biotin, four times the 30mcg adequate intake, as a margin for the days your diet falls short rather than a headline number. It sits alongside 38 other ingredients, every dose printed on the label. For a look at how the rest of the B group is formulated, see the B vitamin forms most labels get wrong.
