What are the signs of riboflavin (B2) deficiency?

Riboflavin deficiency cracks the corners of the mouth and lips, inflames the tongue and throat, and in severe cases damages the liver and nerves.

Who is most likely to run low

Vegans and people who drink little milk are the groups most likely to fall short on riboflavin in wealthy countries.

What this means for you

Riboflavin deficiency has an unusually recognisable face. Cracks at the corners of the mouth, swollen and split lips, a sore throat, a swollen tongue, and eyes that are red and itchy.

In wealthy countries it is uncommon, and it clusters in two groups that are easy to name: vegans, and people who drink little or no milk without deliberately replacing it. Vegetarian athletes are listed separately, because training raises the requirement.

If that is you

Fortified plant drinks, almonds, mushrooms, eggs and nutritional yeast are the practical sources. The daily requirement is small, 1.3 mg for men and 1.1 mg for women, so this is a gap that closes with one habit rather than a programme.

Established. No upper limit was set for riboflavin, because high intakes have not produced harm. Bright yellow urine after a B complex is the excess leaving, not a warning sign.

Riboflavin has a second life at doses a hundred times the daily requirement, taken for migraine, and the two should not be confused. Pooling 22 randomised trials, riboflavin cut migraine attacks by about one and a third a month in adults, while trials in children came out mixed. None of that is a treatment for deficiency, and none of the deficiency signs above respond faster to a large dose than to an ordinary one.

There is no test that answers this

Unsettled. If you go looking for a blood test for riboflavin, there is not one that will tell you what you want to know. No cut-off values have ever been proposed for plasma riboflavin, FAD or FMN, because those track what you ate recently rather than your status over time. The functional test, called EGRAC, measures an enzyme's response to added riboflavin, and it fails completely in people with G6PD deficiency because that enzyme holds FAD too tightly to reveal a shortage. So what settles a suspected deficiency is the distinctive picture, cracked corners of the mouth and a sore swollen tongue, plus whether it responds to treatment. Not a number.

The gene variant that makes riboflavin matter more

Some people need more riboflavin than others for a reason that has nothing to do with their diet. The MTHFR 677TT variant produces an enzyme that holds on less well to its FAD cofactor, and FAD is made from riboflavin. It is not a rare variant. It affects 5 to 15 per cent of most populations, around 20 per cent in parts of Italy and China, and about 30 per cent in Mexico.

What follows from carrying it is less clear than the biology suggests, and the blood pressure claim built on it is covered on the page about riboflavin and medicines. For deficiency, treat it as one more reason that two people eating the same food can end up in different places.

Not for everyone. There is a small group where this stops being a nutrition question. People born without working riboflavin transporters cannot absorb or move the vitamin properly, and they develop hearing loss, bulbar palsy and difficulty breathing. High-dose riboflavin can be life-saving for them, and it works best started soon after symptoms begin. That diagnosis is made by a specialist. It is the reason a neurologist may prescribe a dose this site would otherwise describe as pointless, and it is not a template for anyone else.

Unsettled. Whether people eating no dairy actually fall short is not settled. In Northern Europe riboflavin comes mostly from milk and meat, and one body of survey work reports vegan diets may not supply enough while another reports intakes similar to omnivores. With no agreed blood test to adjudicate, the practical answer is to stop waiting for the argument to resolve and put almonds, mushrooms, fortified plant drinks and nutritional yeast in the week.

What a riboflavin label is allowed to claim

This page is largely about how hard riboflavin status is to pin down. There is a matching fact on the regulatory side, and it is worth knowing before you read a promise on a package.

Established. No food or supplement sold in the United States may legally claim that riboflavin prevents or treats anything. A health claim is unlawful unless the regulations specifically provide for it, and the sections that do run without gaps from 101.72 to 101.83. They cover calcium and vitamin D, dietary lipids, sodium, saturated fat, fibre, fruits and vegetables, folate, sugar alcohols, soluble fibre, soy protein and plant sterols. Riboflavin is not among them, and no qualified claim exists for it either.

Read that as narrowly as it is written. An empty register is a fact about the regulator rather than about the vitamin. It records that the evidence never reached the bar an authorised claim demands. It does not record that riboflavin does nothing, and a page about deficiency is the last place to suggest otherwise, because the deficiency is real, it has a distinctive look, and treating it works.

What the emptiness does do is set your expectations for the shop. If a bottle of riboflavin carries a promise about your energy, your eyes, your nerves or your headaches, that promise has no authorisation behind it, and there is no legal route by which it could have. Take a suspected deficiency to somebody who can treat it, and treat the label as decoration.

Written from the evidence cards and the data on this page, then checked back against the sources. Bioma Learn has no human medical reviewer at this time and we say so rather than invent one. Information, not medical advice. How we verify.

Where to get it from food

• Chicken, liver, all classes, cooked — 1.69 mg per 3 oz (130% DV)
• Almonds, dry roasted — 1.65 mg per 1 cup whole kernels (127% DV)
• Almonds, oil roasted — 1.23 mg per 1 cup whole kernels (94% DV)
• Frankfurter, meatless fortified — 1.17 mg per 1 cup, sliced (90% DV)
• Almonds, blanched — 1.03 mg per 1 cup whole kernels (79% DV)

All riboflavin (B2) sources ranked →

Full guide: Riboflavin: a milk and egg vitamin, and what the migraine trials really show