Biotin for hair: does it work, how much, and what about other vitamins?

Biotin is the first thing many people buy when they get worried about their hair. It is cheap, it is a real vitamin, and the packaging is confident. It also has a plausible story attached: people who are seriously short of biotin can lose their hair.

The trouble lies in the step from that fact to "so extra biotin will help mine". That step has very little research behind it, and taking biotin carries a specific risk that most people have never heard of.

What biotin does

Biotin, also known as vitamin B7, is a B vitamin your body uses to help process fats, carbohydrates and protein. Hair loss, along with skin and nail changes, can be a symptom of real deficiency. The American Academy of Dermatology includes low biotin among the nutrient shortages that can cause noticeable hair loss, and says hair can regrow once the levels are corrected.

That part is not in dispute. The question is how many people it applies to.

What the evidence for biotin and hair shows

The most-cited summary is a 2017 review in Skin Appendage Disorders, by Patel, Swink and Castelo-Soccio. The authors searched for case reports and clinical trials of biotin for hair and nails. What they found:

• 18 reported cases of biotin being used for hair or nail problems. All of them showed some improvement.
• Every one of those people had an underlying condition behind their poor hair or nail growth, such as acquired or inherited biotin deficiency, brittle nail syndrome or uncombable hair.
• No randomised trials showing that biotin helps healthy people.

The authors concluded that they found no evidence of benefit from biotin outside known deficiency. The US National Institutes of Health's fact sheet is similarly plain: claims for hair, skin and nails are supported, at best, by only a few case reports and small studies.

So there is a gap between what is known and what is sold. That doesn't prove biotin does nothing for anyone, because absence of trials is not proof of absence. But the people selling it have not shown that it works.

Who might really be short of biotin?

True deficiency is uncommon in people who eat a balanced diet. The review links it with:

• Eating a lot of raw egg white, which contains a protein that binds biotin
• Certain medications
• Pregnancy
• Alcohol use disorder
• Rare inherited enzyme conditions

If any of those apply and you have noticed hair changes, raise it with your doctor. Do not assume this is the cause, and do not treat it by yourself.

How much biotin for hair growth?

No dose has been shown to grow hair in people who are not deficient. These are the figures you are likely to come across:

A lot more is not obviously better, and the highest doses are the ones most likely to cause the following problem.

The biotin blood test warning

This is the part of the biotin story that deserves more attention than the hair claims.

Many modern laboratory tests use a biotin-based chemical reaction. When there is a lot of biotin in your blood, it can interfere with that reaction and give a result that is wrong. The US Food and Drug Administration issued a safety warning about this in November 2017 and updated it in November 2019.

Depending on how the test is designed, the result can be falsely high or falsely low. The examples reported include:

• Troponin, the blood test used to help detect heart attacks. A falsely low result could mean a heart attack is missed. The FDA has received a report of a patient on high-dose biotin who died after falsely low troponin results.
• Thyroid tests. Falsely abnormal results have led to wrongly diagnosing Graves' disease in several patients who were taking biotin.
• Other tests, including some viral hepatitis panels, have also been reported as potentially affected.

Biotin at the level you get from food is not high enough to cause this. The concern is with supplements, and the FDA has not set a precise "safe" dose. Some test manufacturers have since altered their tests, but others have not.

This matters particularly for hair, because a blood test for thyroid function is one of the most common checks for anyone seeing a doctor about hair loss. Biotin taken for your hair could give you a misleading result from the very test meant to explain your hair loss.

Vitamins for hair growth: the wider picture

The best general overview is a 2019 review in Dermatology and Therapy, by Almohanna and colleagues. It looked at vitamins and minerals in non-scarring hair loss, and concluded that larger, well-designed trials are still needed to test whether supplements help. The short version looks like this.

There's a pattern here. These nutrients matter when you lack them, and adding more on top of an adequate intake has not been shown to help. In the case of vitamin A and selenium, more can actually cause the problem you are trying to fix.

"Hair growth" blends deserve the same questions as anything else: how many trials, how many people, compared with what, and for how long? Be wary of any mix that contains several of these ingredients, because it can be hard to tell how much you are getting in total.

Foods for hair growth

No food has been shown to make healthy hair grow faster. But hair is sensitive to shortages, and severe protein malnutrition can cause hair loss. Crash diets are a known trigger of delayed shedding. So the useful advice is rather dull:

• Eat enough overall. If your shedding followed a period of heavy dieting, that is the first thing to look at.
• Get enough protein. Meat, fish, eggs, dairy, beans, lentils and tofu all count.
• Pay attention to iron. Red meat, beans, lentils and leafy greens all provide it, and it is worth extra attention if you have heavy periods or eat little meat.
• Include biotin-containing foods naturally. Eggs, liver and some seeds and nuts contain it. Cooked eggs are fine; raw egg white is the problem.

Some studies have linked particular foods and nutrients with better hair, but those associations do not show that any food causes faster growth.

What to do instead of guessing

If your hair is shedding or thinning, biotin is unlikely to be the answer, and taking it first could get in the way of finding the actual one. In order:

1. Work out what kind of loss you have, starting with the shedding or breakage check. Breakage is a fibre problem, and no vitamin fixes that.
2. See a doctor if it is more than breakage, and ask about blood tests.
3. Correct whatever those tests actually find.
4. If you do decide to try a supplement, try only one, tell your doctor, and judge it by monthly photos over at least six months.

If what you really want is longer hair, how to grow hair faster explains where length is actually lost.

See a doctor if your hair loss is sudden, patchy or getting worse, or comes with a sore or scaly scalp, tiredness or other symptoms. And please do not delay medical care for hair loss while you wait to see whether a supplement works.