Riboflavin: Benefits, Dosage, and Safety

What riboflavin is

Riboflavin, also called vitamin B2, is one of the water-soluble B vitamins. It is naturally present in some foods, added to some fortified foods, and available as a dietary supplement. It is the essential building block of two major coenzymes, flavin mononucleotide (FMN, also called riboflavin-5'-phosphate) and flavin adenine dinucleotide (FAD). More than 90 percent of dietary riboflavin comes as FAD or FMN, with the rest as free riboflavin and glycosides or esters. Most is absorbed in the proximal small intestine, and the body stores only small amounts in the liver, heart, and kidneys. The body absorbs little riboflavin from single doses beyond about 27 mg, and excess absorbed amounts are excreted in urine, which turns bright yellow. Riboflavin is yellow and fluoresces under ultraviolet light, and light can rapidly inactivate it, which is why milk is not typically stored in clear glass.

What it does

• Serves as the core of the coenzymes FAD and FMN, which drive energy production from fats, carbohydrates, and protein
• Supports normal cellular function, growth, and development
• Aids metabolism of fats, drugs, and steroids
• Is required (as FAD) for converting the amino acid tryptophan into niacin (vitamin B3)
• Is needed (as FMN) to convert vitamin B6 into its active coenzyme pyridoxal 5'-phosphate
• Helps maintain normal blood levels of the amino acid homocysteine
• Supports mitochondrial function

How much riboflavin per day

These are population reference values from the NIH and the Dietary Reference Intakes. They are targets for healthy people, not personal prescriptions. The last column is the Tolerable Upper Intake Level, the most you should get from all sources combined.

Deficiency and who is at risk

Riboflavin deficiency (ariboflavinosis) is extremely rare in the United States. Signs and symptoms include skin disorders, hyperemia (excess blood) and edema of the mouth and throat, angular stomatitis (lesions at the corners of the mouth), cheilosis (swollen, cracked lips), hair loss, reproductive problems, sore throat, itchy and red eyes, and degeneration of the liver and nervous system. People with riboflavin deficiency typically also have deficiencies of other nutrients. Severe, prolonged deficiency can lead to anemia and cataracts. Earlier changes are easily reversed, but supplements rarely reverse later anatomical changes such as cataract formation.

Who may need more

• Vegetarian and vegan athletes
• Pregnant and lactating women with low intake of meat and dairy
• Vegans and people who consume little or no milk
• People in food-insecure settings reliant on food assistance
• People with riboflavin transporter deficiency, for whom high-dose riboflavin can be a life-saving treatment

Food sources

Beef liver (pan fried, 3 oz: 2.9 mg), riboflavin-fortified breakfast cereals (1 serving: 1.3 mg), fortified instant oats (1 cup: 1.1 mg), plain fat-free yogurt (1 cup: 0.6 mg), 2% milk (1 cup: 0.5 mg), beef tenderloin (3 oz: 0.4 mg), clams (3 oz: 0.4 mg), almonds (1 oz: 0.3 mg), Swiss cheese (3 oz: 0.3 mg), eggs, and enriched grains and cereals. Milk and milk drinks, bread and bread products, meat-based mixed foods, and ready-to-eat cereals are the largest contributors in the U.S. diet. Roughly twice as much riboflavin is lost in cooking water when foods are boiled versus steamed or microwaved.

Forms and absorption

Available as free riboflavin (the most common supplement form) and as riboflavin 5'-phosphate. Sold as standalone riboflavin supplements, in B-complex products, and in multivitamin/mineral supplements, which commonly provide 1.3 mg (100 percent of the Daily Value). About 95 percent of food-bound riboflavin as FAD or FMN is bioavailable up to a maximum of about 27 mg per meal or dose, and the bioavailability of free riboflavin is similar to that of FAD and FMN.

Safety, excess and interactions

Too much

Intakes of riboflavin from food that are many times the RDA have no observable toxicity, likely because its solubility and intestinal absorption are limited. Adverse effects from high intakes from foods or supplements (400 mg/day for at least 3 months) have not been reported, so the Food and Nutrition Board did not establish a Tolerable Upper Intake Level. A harmless bright-yellow discoloration of the urine can occur with high supplemental doses. The FNB nonetheless urges caution about consuming excessive amounts, since limited data do not prove that high intakes are free of adverse effects.

Interactions to know

• Per NIH ODS, riboflavin is not known to have any clinically relevant interactions with medications.
• Prolonged phototherapy (for newborn jaundice or skin disorders) can degrade riboflavin and contribute to deficiency, since ultraviolet and visible light rapidly inactivate the vitamin.

How status is measured

Riboflavin status is not routinely measured in healthy people. The most stable, sensitive marker is the erythrocyte glutathione reductase activity coefficient (EGRAC): 1.2 or less indicates adequate status, 1.2 to 1.4 marginal deficiency, and greater than 1.4 deficiency (EGRAC cannot be used in people with glucose-6-phosphate dehydrogenase deficiency). A second method is fluorometric measurement of 24-hour urinary riboflavin excretion; at least 120 mcg/day reflects adequacy while less than 40 mcg/day indicates deficiency, though this reflects recent intake more than long-term status.

Regulated as a dietary supplement ingredient under DSHEA, not FDA-approved to diagnose, treat, cure, or prevent disease. The FDA Daily Value (DV) for riboflavin is 1.3 mg for adults and children age 4 years and older. FDA does not require food labels to list riboflavin content unless riboflavin has been added to the food.

What the evidence supports

We grade the strength of evidence behind each common reason people take riboflavin, mirroring how the NIH describes it.