Vitamin B7 (Biotin)

Biotin, also called vitamin B7 or vitamin H, is a water-soluble B vitamin. It is a cofactor (a helper) for five enzymes called carboxylases, says the NIH (the US National Institutes of Health). These enzymes carry out key steps in the metabolism of fatty acids, glucose and amino acids.

People cannot make biotin, so it comes from food. Bacteria in the large intestine make some too, but how much that adds is unclear.

Biotin is best known as a hair, skin and nail supplement, and that is where the evidence is thinnest. The NIH says these claims rest, at best, on a few case reports and small studies. Reviews find gains in people with a deficiency or a rare hair or nail disorder, and no high-quality trial in healthy people.

The hair and nail studies we found used 1 to 10 mg a day. That is about 33 to 333 times the 30 mcg adequate intake (mcg means micrograms, millionths of a gram).

Two facts surprise most readers. Raw egg white contains avidin, a protein that binds biotin and blocks its absorption, and cooking disables it.

And biotin supplements can make blood tests lie. The FDA warned in 2017 that biotin can cause incorrect lab results that may go undetected. It reported that a patient taking high levels of biotin died after a falsely low result on troponin, a heart attack test.

Health benefits of biotin

• ★★★EU-approved claims: normal hair, skin, mucous membranesThe EU allows foods that are a source of biotin to claim it helps maintain normal hair, skin and mucous membranes. It does not claim that extra biotin grows hair or treats hair loss.
• ★★High-dose biotin did not clearly help MS disabilityAt 300 mg a day, biotin pills did not clearly improve disability in progressive multiple sclerosis (MS). Walking was mixed: pooled trials found people 2.06 times as likely to improve their 25-foot walk time, but the biggest trial found no clear gain.
• ★★High-dose biotin can give false lab test resultsIn MS trials, 4.7% of people on 300 mg or more a day had affected lab tests (31 of 662), against none on placebo. At 10 mg a day for 7 days, 9 of 23 biotin-based tests gave wrong results in 6 adults.
• ★Little evidence it helps hair in healthy peopleA review found biotin improved hair or nails only in 18 cases that had an underlying cause, such as deficiency. A 2024 review found only 3 eligible hair studies, and its best trial found no difference in growth.
• ★Firmer nails in brittle-nail studies, with no placeboIn an uncontrolled study, 41 of 45 people assessed (71 were treated) had firmer nails on 2.5 mg of biotin a day. In a 50-person trial, adding 10 mg of biotin pills to a nail lacquer raised responders from 53% to 80%, a borderline gap.

Foods high in biotin

Oysters lead our ranking per serving: 3 oz (85 g) gives 34.9 mcg, 116% of the 30 mcg Daily Value (the FDA label value). Sunflower seeds (28.3 mcg per ounce), hazelnuts (24.9 mcg) and almonds (23.4 mcg) follow. One large egg gives 11.8 mcg.

Per 100 g, sunflower seeds (99.8 mcg), hazelnuts (87.8 mcg) and almonds (82.5 mcg) are richest. Soybeans are not in our ranking. Per 100 kcal, kale (103 mcg), oysters (50.6 mcg) and white mushrooms (44.7 mcg) lead.

Beef liver is not in our ranking, but the NIH lists cooked beef liver at 30.8 mcg in 3 oz, 103% of the Daily Value. The NIH names organ meats, eggs, fish, meat, seeds, nuts and certain vegetables such as sweet potatoes as the richest sources. It lists a cooked egg at 10.0 mcg and canned pink salmon at 5.0 mcg in 3 oz. A cooked pork chop gives 3.8 mcg in 3 oz.

Treat food numbers for biotin with care. A team that measured 87 foods in the lab found that published values were likely to be inaccurate. Only 7 of 51 foods agreed within the margin of error, and measured values ran from 247 times higher to 36% lower than published ones.

Databases also differ. The NIH table lists roasted sunflower seeds at 2.6 mcg per ¼ cup. Our ranking uses the Danish Frida food database and shows 28.3 mcg in 1 oz. Use the ranking to see which foods are richer, not as an exact count.

How much you absorb also varies. Most biotin in cereals and meats is bound to protein and must be freed by digestion. Plant variety and season change the biotin in cereal grains, and the NIH says canning can reduce it. Eat eggs cooked, since raw egg white holds avidin.

How biotin works

Most of this is established biochemistry, described in reviews, cell work and a few human feeding experiments, not in trials of extra biotin. Four ideas cover it: biotin helps five enzymes, and raw egg white can lock it up. The gut takes it in on a shared carrier, and in large amounts it can fool lab tests. Here is each one, and what has been seen in people.

It helps five enzymes

Biotin is a cofactor for acetyl-CoA carboxylase 1 and 2, pyruvate carboxylase, methylcrotonyl-CoA carboxylase (MCC) and propionyl-CoA carboxylase (PCC), according to the NIH. A 2024 Nordic review describes their work. They build fatty acids, make glucose from other fuels, and convert pyruvate to oxaloacetate in the citric acid cycle. They also break down branched-chain amino acids and odd-chain fatty acids.

The NIH adds that biotin also takes part in histone changes (changes to the proteins that package DNA) and gene regulation. The review treats this as a possible role outside the enzymes.

Low biotin leaves a trace in urine

When biotin runs short, the MCC step slows. A by-product of the amino acid leucine, 3-hydroxyisovaleric acid (3-HIA), then builds up in urine. In 10 adults whose diet held enough avidin to bind seven times its biotin, urinary 3-HIA rose and urinary biotin fell within 20 days. Blood biotin did not clearly drop.

In 7 adults fed egg white for 28 days, PCC activity in white blood cells fell below normal in all of them by day 14. The NIH lists urinary 3-HIA above 3.3 mmol/mol creatinine as a sign of deficiency. It says blood biotin is not a good indicator of marginal deficiency.

Raw egg white can lock it up

Avidin is a glycoprotein (a protein with sugars attached) in raw egg white. It binds dietary biotin tightly and prevents its absorption in the gut, and cooking denatures (unfolds) it, according to the NIH. Deficiency has been reported in people who ate large amounts of raw egg white over a long time, as EFSA and the Nordic review note. A cooked egg is a source of biotin, with 10 mcg in the NIH food table.

It crosses the gut wall on a shared carrier

Most biotin in food is bound to protein. Gut enzymes break the protein down to biocytin and small biotin peptides. The enzyme biotinidase then frees the biotin for absorption in the small intestine, the NIH explains.

Free biotin crosses the gut wall on the sodium-dependent multivitamin transporter, which also carries pantothenic acid and lipoate. In human-derived gut and liver cells it is the main, perhaps the only, uptake route at normal concentrations. EFSA says the nutritional meaning of the shared carrier is not known. At pharmacologic (drug-level) doses, biotin taken by mouth is absorbed completely.

In large amounts it can fool lab tests

Many lab tests, including those for thyroid hormones, troponin and 25-hydroxyvitamin D, use biotin and streptavidin, a protein that grips biotin. Excess biotin in the blood can disturb that binding. Six healthy adults took 10 mg a day for a week. Then 9 of 23 such tests gave wrong results, and none of the 14 tests without biotin did.

Depending on the test design, the error can run in either direction, falsely high or falsely low. A case report with a review of the literature found the same.

What has been seen in people

The clearest human findings are about shortage and excess. Biotin is needed. Children on long-term intravenous feeding without it lost hair and developed a rash that cleared with biotin. Children with biotinidase deficiency who get biotin from birth develop normally.

Marginal shortage shows up in urine markers in pregnancy and in smokers, though what it means for health is still unclear. At the other end, doses of 10 mg and more disturb lab tests. For hair and nails, the gains seen so far are in people with a deficiency or a rare disorder, as the study cards above show.

How much biotin do you need?

Adults have an adequate intake of 30 mcg of biotin a day in the US and 40 mcg in the EU. These are adequate intakes, not recommended allowances, because the data were too thin to set an average requirement. The label value is 30 mcg in the US (the Daily Value) and 50 mcg in the EU (the EU Reference Intake).

There are no national US estimates of intake. But the NIH says average intakes from food in other western populations are about 35 to 70 mcg a day. So most people there eat enough.

An EFSA report on five EU countries gives 26 to 50 mcg for adults under 65, according to the Nordic review. Intake estimates are rough, because food tables for biotin are imprecise.

In pregnancy the US adequate intake stays at 30 mcg and EFSA’s is 40 mcg. While breastfeeding it is 35 mcg in the US and 45 mcg in the EU.

For US children, the values are 8 mcg at ages 1 to 3 and 12 mcg at ages 4 to 8. They are 20 mcg at ages 9 to 13 and 25 mcg at ages 14 to 18. Infants get 5 mcg up to 6 months and 6 mcg from 7 to 12 months in the US.

The EU values are 20, 25 and 35 mcg for ages 1 to 3, 4 to 10 and 11 to 17. Neither body sets a higher value for older adults.

Some groups may need more, but no official value says so. In a controlled feeding study that gave 57 mcg of biotin a day, pregnant women excreted 69% more 3-HIA than controls. Breastfeeding women excreted 76% more of the breakdown product bisnorbiotin. The authors suggest that intakes above the current recommendations may be needed in pregnancy and breastfeeding.

Smokers break biotin down faster, and some anticonvulsants do the same, as the cards above show. The NIH adds that at least a third of pregnant women develop marginal biotin deficiency in spite of normal intakes. Its clinical meaning is not yet understood.

Biotin deficiency: signs and who is at risk

Deficiency is rare. The NIH says severe deficiency has never been reported in healthy people eating a normal mixed diet. When it occurs, signs appear gradually. Hair thins and can progress to loss of all body hair, and a scaly red rash appears around the eyes, nose, mouth and perineum.

Other signs are conjunctivitis, brittle nails, and in adults depression, lethargy, hallucinations and tingling in the arms and legs. Seizures and skin infection can follow. Infants can show low muscle tone, lethargy and developmental delay.

Deficiency has been reported in people who ate large amounts of raw egg white for a long time. It has also been seen in patients on long-term intravenous feeding without biotin. It also occurs in biotinidase deficiency, a rare inherited disorder in which the body cannot release free biotin from food. Without treatment it causes neurological and skin symptoms, and in the profound form it can lead to coma or death.

Lifelong oral biotin started at birth prevents the symptoms. That is why newborns are screened for it in all US states and in many other countries.

The NIH also lists chronic alcohol exposure, which inhibits absorption: plasma biotin was low in 15% of people with chronic alcoholism. Pregnancy, breastfeeding and anticonvulsant drugs are on its list too. Plant-based diets are not a risk factor in the one study we found: vegans excreted more biotin than people on mixed diets.

Testing is not simple. The most reliable markers are biotin-dependent enzymes in white blood cells and urinary 3-HIA above 3.3 mmol/mol creatinine. Blood biotin hardly falls in marginal deficiency, according to the NIH. The Nordic review notes that no single marker cleanly separates deficient from sufficient people.

Forms of biotin: absorption and effects

Biotin supplements are free biotin, sold alone or inside B-complex and multivitamin products, as the NIH describes. Biotin in food is mostly bound to protein and has to be freed during digestion. The trials on this page used an ordinary supplement dose of 1 to 10 mg, or combination products. A pharmaceutical-grade product (MD1003) was given at 300 mg a day for multiple sclerosis.

The honest bottom line: free biotin is absorbed almost completely, even at large doses, so the form matters little for absorption. What differs between products is the dose and the other ingredients. We found no study that compared tablets, capsules, gummies or liquids, and none showing that one form works better for hair or nails. Nor did we find a trial of any form for hair in healthy people.

Several outcome trials used mixtures, and their results cannot be credited to biotin alone. Examples are chromium picolinate with biotin in diabetes, and a nail lacquer with biotin in brittle nails.

Form	Activity or conversion	What studies show	Source
Free biotin (supplements)	Not stated. The NIH puts absorption of oral free biotin at 100%, even at up to 20 mg a day	In 6 healthy adults, urinary recovery of biotin and its metabolites was similar after oral doses of 8.2 and 81.9 micromol, which suggests complete absorption. We found no trial comparing it with other forms for hair or nails.	1, 2
Biotin in food (protein-bound)	Freed to biocytin and biotin peptides by gut enzymes, then to free biotin by biotinidase (NIH)	Absorption varies by food, and avidin in raw egg white blocks it. We found no study that measured the share absorbed from foods against supplements.	1, 3
Biotin in B-complex and multivitamin products	Not stated	A 1989 check found that labeled biotin amounts matched the assay in most products, and that some products with no biotin label held meaningful amounts, especially with liver or yeast extract.	1, 4
Pharmaceutical-grade biotin (MD1003), 300 mg a day	Not stated	Used in multiple sclerosis trials: disability reversed in 12.6% against none in 154 people in one trial, but no significant gain in 642 people in the larger one, and no gain in vision in 93 people. It also caused lab test interference.	5, 6, 7
Biotin with chromium picolinate or in a nail lacquer combination	Not stated	With chromium, the 2-hour glucose curve fell 9.7% against a 5.1% rise on placebo in 43 people; the trial cannot separate biotin from chromium. With a lacquer, 80% against 53% responders compared with lacquer alone in 50 people.	8, 9
Biotin made by gut bacteria	Not stated	Bacteria in the large intestine make biotin and the gut can absorb it, but how much this adds to human intake is unclear.	3, 10

Here are the 2 studies that compared doses or checked what products contain.

Is biotin safe? Supplements, dose and interactions

Biotin from food is not a safety concern, and neither the US nor the EU has set an upper level. The US Food and Nutrition Board could not set a tolerable upper intake level. There is no evidence of biotin toxicity in people at high intakes.

The NIH notes several studies with no adverse effects at 10 to 50 mg a day. In people with biotinidase deficiency, it notes no toxicity at up to 200 mg a day by mouth or 20 mg a day by vein.

In the EU, the Scientific Committee on Food could not derive an upper level in 2001. It judged that observed intakes from all sources are not a health risk for the general population, as EFSA reports. No upper level means no known toxicity, not no risk. The lab-test problem below starts well below the doses studied for toxicity.

• Lab tests. Very high intakes can interfere with tests that use biotin and streptavidin, including thyroid hormones, 25-hydroxyvitamin D and troponin, the NIH says. Results can come out falsely high or falsely low. In 6 healthy adults, 10 mg a day for a week affected 9 of 23 such tests. The NIH lists cases that falsely suggested Graves’ disease (an overactive thyroid) in people taking 10 to 300 mg a day. It also lists a single 10 mg dose that interfered with thyroid tests within 24 hours. The FDA reported that a patient taking high levels of biotin died after a falsely low troponin result. It keeps a list of troponin tests still subject to interference. It advises health care providers to ask about biotin, tell the lab and consider interference when results do not fit the clinical picture. It also said the data were not enough to say how long biotin takes to clear from the blood. If you take biotin, tell your doctor and the lab before any blood test, and ask whether to stop it first. One modeling study found the risk very low for a single troponin T assay, but that does not cover other tests.
• Doses and side effects. The trials on this page gave 1 to 10 mg a day for hair and nails and 300 mg a day in multiple sclerosis. In the large MS trial, serious adverse events were equally common on biotin and placebo (26% in both). In the pooled MS trials, any adverse event and any serious event did not differ from placebo. But 4.7% of people on biotin had lab test interference, against none on placebo.
• Medicines. The NIH lists anticonvulsants as lowering biotin. Carbamazepine, primidone, phenytoin and phenobarbital were linked to lower blood biotin in 264 people with epilepsy, probably because treatment speeds up biotin breakdown. People who take these drugs regularly should talk to their doctor about their biotin status.
• Who should ask a doctor. Anyone due for blood tests such as thyroid, heart or vitamin D tests. People who are pregnant or breastfeeding, because prenatal vitamins can already contain biotin and needs may be higher. People on anticonvulsants, and anyone with hair loss that is sudden or lasting. The reviews above found gains only in people with a specific underlying problem, so it is worth finding the cause rather than guessing.

How to get more biotin

• Eat a mix of foods. The NIH lists 30.8 mcg in 3 oz of cooked beef liver and 10 mcg in a cooked egg. Our ranking has oysters (34.9 mcg in 3 oz), sunflower seeds and nuts. Single servings of some of these, such as liver or oysters, exceed the 30 mcg adequate intake.
• Cook your eggs. Raw egg white holds avidin, which binds biotin, and cooking denatures it. Deficiency from eggs has been reported only with large amounts of raw egg white over a long time.
• Skip high-dose pills unless a doctor prescribes them. Average intakes in other western populations are about 35 to 70 mcg a day. Hair and nail gains are shown only in deficiency, and large doses can disturb lab tests.

History of biotin

Biotin was found by following a puzzle. By the 1920s it was clear that the “water-soluble B” factor in yeast was several substances. Biotin and pantothenic acid were recognized as vitamins somewhat later, through work on growth factors for microbes.

Along the way, researchers saw that rats fed raw egg white as their main protein lost hair and developed skin disease and nerve problems. A factor found in liver protected them. Boas published on the nutritive properties of egg white in 1927.

The substance had several names. In 1936 Fritz Kögl and Benno Tönnis crystallized a yeast growth factor from egg yolk and called it biotin. Paul György called the protective factor in liver vitamin H, and a third substance was known as coenzyme R.

In 1940 György and Vincent du Vigneaud, with colleagues, reported that vitamin H and biotin were the same substance. The harmful part of raw egg white turned out to be avidin, which binds biotin. Harris and colleagues made biotin in the lab in 1943.

Human deficiency came to light more slowly. In the 1980s Donald Mock described biotin deficiency in children on long-term intravenous feeding. His group later showed that marginal deficiency is common in pregnancy. Biotinidase deficiency, a rare inherited disorder, is now screened for in newborns in all US states. In 2017 the FDA warned that high-dose biotin can distort lab tests.

Frequently asked questions about biotin

Does biotin make hair grow?

Only if hair loss comes from a biotin deficiency or a rare hair disorder, as far as studies show. A review of 18 cases found that every person who improved had an underlying cause. A 2024 review found 3 studies, and the best of them saw no difference in hair growth. The EU authorizes a claim for maintaining normal hair. It applies to foods that are at least a source of biotin, and does not say that extra biotin grows hair. If your hair is thinning, ask a doctor to look for the cause first.

Does biotin help brittle nails?

Possibly, but the evidence is weak. In an uncontrolled study, 41 of 45 people (91%) had firmer, harder nails after about 5.5 months on 2.5 mg a day. In a randomized trial of 50 people, a nail lacquer plus 10 mg of biotin gave a 50% improvement in 80% of people. With the lacquer alone, 53% improved that much. That gap was borderline. Neither study tested healthy people, and neither had a placebo group.

Can biotin affect blood test results?

Yes. High-dose biotin can make tests that use biotin and streptavidin read falsely high or falsely low. In 6 healthy adults, 10 mg a day for a week affected 9 of 23 such tests and none of 14 tests without biotin. The FDA reported that a patient taking high levels of biotin died after a falsely low troponin result. Tell your doctor and the lab if you take biotin, and ask whether to stop it before a blood test.

Can you take biotin every day?

At food amounts, yes. Neither the US nor the EU has set an upper level. The NIH notes studies with no adverse effects at 10 to 50 mg a day. But supplements are unnecessary for most people. Their average intakes in other western populations are about 35 to 70 mcg a day, against an adequate intake of 30 mcg. And daily use can disturb lab tests.

Is raw egg white bad for biotin?

Yes, if you eat a lot of it over a long time. Raw egg white contains avidin, which binds biotin and stops its absorption, and cooking denatures it. In an experiment, 10 adults ate a diet with enough avidin to bind seven times their dietary biotin. Within 20 days they had signs of lower biotin status. A cooked egg gives 10 mcg of biotin, according to the NIH.

Which foods are highest in biotin?

In our ranking, oysters lead per serving with 34.9 mcg in 3 oz. Next come sunflower seeds (28.3 mcg per ounce), hazelnuts (24.9 mcg) and almonds (23.4 mcg). The NIH lists cooked beef liver at 30.8 mcg in 3 oz and a cooked egg at 10 mcg. Food tables disagree on biotin, so treat the numbers as a guide.

Do you need extra biotin in pregnancy?

The adequate intake in pregnancy is 30 mcg in the US and 40 mcg in the EU, the same as for other adults. In a randomized trial in 26 pregnant women with a raised marker of low biotin, 300 mcg a day for 14 days lowered the marker. The NIH says at least a third of pregnant women develop marginal deficiency. No human study has shown that low biotin causes birth defects, although it does in mice. Ask your doctor, since prenatal vitamins can already contain some.

Can biotin treat multiple sclerosis?

Not at present. A first trial in 154 people with progressive MS found disability reversal in 12.6% on 300 mg a day, against none on placebo. But the larger SPI2 trial in 642 people found no clear gain in disability or walking speed. A meta-analysis found a possible walking benefit of moderate certainty, and more lab test interference. The SPI2 authors conclude that biotin cannot be recommended for progressive MS.