Quick answer

Riboflavin, or vitamin B2, is a B vitamin your body uses to make energy and to process fats, other vitamins and some medicines. Adults need 1.1 to 1.3 mg a day, and most Americans get enough from milk, eggs, meat and fortified grains. Extra riboflavin can turn urine bright yellow, a minor and expected effect.^1,2

Key facts

The gut absorbs at most about 27 mg of riboflavin at a time.^1,3
Fewer than 6% of people in the United States fall short of the average requirement.²
People who are vegan or eat little dairy are among the groups most likely to run low.^1,2
No upper limit is set, and no harm has been reported even at 400 mg a day for three months.²

What riboflavin does

Riboflavin is one of the water-soluble B vitamins. It occurs naturally in some foods, is added to many others, and is sold on its own, in B-complex products and in multivitamins.^1,2

Riboflavin is part of two coenzymes, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), that many enzymes need.²

Those coenzymes have major roles in energy production, in cell growth and development, and in the breakdown of fats, steroids and medicines.²

Riboflavin's coenzymes are needed to make niacin from the amino acid tryptophan and to turn vitamin B6 into its active form. FAD is also needed in the folate cycle.^2,4

Riboflavin is yellow and glows under ultraviolet light.²

What the evidence shows

EFSA, the European food safety agency, reviewed the science behind each statement below, and the EU now permits them on foods that supply a meaningful amount of riboflavin. We grade them moderate: they describe the job riboflavin does when your intake is adequate, not an extra effect from a bigger dose.⁵

Contributes to normal energy-yielding metabolism*^1,2,5

Moderate evidence

Riboflavin is part of FMN and FAD, coenzymes with major roles in energy production. 'Contributes to normal energy-yielding metabolism' is the wording European regulators permit for riboflavin after EFSA review. It does not mean extra riboflavin gives more energy to someone who already gets enough.

Amount studied: Recommended intake: 1.3 mg a day for men and 1.1 mg for women, from all sources

Contributes to normal functioning of the nervous system*⁵

Moderate evidence

A role accepted by EFSA and included in the EU list of permitted nutrient-function statements. It describes what riboflavin does when you get enough. It does not mean extra riboflavin changes how the brain or nerves work in people who already get enough.

Amount studied: Recommended daily intake from food and supplements

Contributes to the maintenance of normal skin, mucous membranes and vision*^2,4,5

Moderate evidence

Three separate statements in the EU list of permitted nutrient-function statements, each accepted after EFSA review. EFSA lists changes in the skin, lips, mouth and throat among the signs seen when intake is very low, and NIH adds itchy, red eyes. It does not mean extra riboflavin changes skin or eyesight in people who already get enough.

Amount studied: Recommended daily intake from food and supplements

Contributes to the maintenance of normal red blood cells and the normal metabolism of iron*^4,5,6

Moderate evidence

Two statements in the EU list of permitted nutrient-function statements, accepted after EFSA review. EFSA explains that low riboflavin is thought to hinder the release of stored iron for making red blood cells. In a UK trial, 123 women aged 19 to 25 with low riboflavin status took 2 mg, 4 mg or a placebo daily for 8 weeks: riboflavin raised their status in line with the dose, and hemoglobin rose most in women whose status was lowest at the start. Iron intake and iron absorption did not change.

Amount studied: 2 or 4 mg a day for 8 weeks in women with low riboflavin status

Only the red blood cell statement is backed here by a trial of riboflavin itself, and that trial enrolled young women whose riboflavin status was low to begin with.⁶

How much you need

Men need 1.3 mg of riboflavin a day from all sources.^1,2

Women need 1.1 mg a day, 1.4 mg during pregnancy and 1.6 mg while breastfeeding.^1,2

Labels use a Daily Value of 1.3 mg. European reference values are set higher, and the dosage guide compares the two and lists the amounts for children and teens.^2,4

Where to get it

Eggs, organ meats such as kidneys and liver, lean meats, low-fat milk, some vegetables such as mushrooms and spinach, and fortified cereals, bread and grain products all provide riboflavin.¹

The largest sources of riboflavin for US adults are milk and milk drinks, bread, dishes based on meat, ready-to-eat cereals and dishes based on grains.²

Dairy foods are a major source, and NIH lists people who eat no dairy among those more likely to run short. Fortified cereals, almonds, mushrooms and spinach help fill the gap in plant-based diets.^1,2

Forms in supplements

Most supplements contain riboflavin in its free form. Multivitamins commonly provide 1.3 mg, 100% of the Daily Value.²

Some supplements use riboflavin 5'-phosphate, also called FMN, one of the vitamin's two coenzyme forms.²

NIH reports that free riboflavin is absorbed about as well as FAD and FMN, the coenzyme forms found in food.²

What's in ours

What’s in ours

Men's Multi: Vitamin B2, 7.5 mg per serving, from the label

Our multivitamin's amount is several times the recommended intake and above the 2 to 4 mg a day used in the trial above, yet well below the roughly 27 mg the gut can take up at once. No upper limit applies to riboflavin.^2,6

Who is more likely to run low

Riboflavin deficiency is very rare in the United States. NIH names the groups more likely to run low: vegetarian athletes, pregnant and breastfeeding women and their babies, vegans, people who eat no dairy, and people with riboflavin transporter deficiency, a rare inherited neurological disorder.^1,2

Exercise puts extra demand on the pathways that use riboflavin, and sports nutrition groups say vegetarian athletes may run short.²

Low thyroid hormone and some other diseases can also cause riboflavin deficiency. It rarely occurs alone: people who are short of riboflavin are usually short of other nutrients too.²

Side effects and who should ask first

Urine often turns bright yellow, because riboflavin is yellow and the body passes the extra in urine. Medical experts describe this discoloration as a minimal side effect.²

No adverse effects have been reported from high riboflavin intakes from food or supplements, including 400 mg a day for at least three months, though experts urge caution with very large amounts.^2,4

No upper limit has been set for riboflavin, because no adverse effects from high intakes have been reported. The gut absorbs at most about 27 mg at a time, and the excess leaves in urine.^2,4

NIH says riboflavin is not known to have clinically relevant interactions with medicines. Still tell your pharmacist about it, along with every other supplement and medicine you take.^1,2

Ask first if you are pregnant or breastfeeding and want more than a prenatal vitamin or multivitamin provides
Ask first before high doses such as 400 mg a day, which are used for migraine under medical guidance¹
Ask first if you have a condition that affects absorption, such as riboflavin transporter deficiency, or low thyroid hormone²

Questions people ask

Is riboflavin the same as vitamin B2?

Yes. Riboflavin is vitamin B2. Supplement labels list it as riboflavin or as riboflavin 5'-phosphate, one of its coenzyme forms.²

Why does riboflavin turn urine yellow?

Riboflavin is a yellow, naturally fluorescent vitamin. The body absorbs a limited amount, keeps little of it, and passes the extra in urine, which can turn it bright yellow.^1,2

Does riboflavin help hair?

NIH lists losing hair among the signs of a severe shortage, which is very rare in the United States. Nothing in the sources we use shows that extra riboflavin changes hair in people who already get enough.¹

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*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.