Vitamin B2

What Is Riboflavin (Vitamin B2)?

Riboflavin is a water-soluble B vitamin with a color: its name comes from the Latin flavus, yellow, and it is approved in the EU as a yellow food coloring, E101. The body stores very little of it, so what is not used leaves in urine, which is why a B-complex tablet turns urine bright yellow.

What Riboflavin Does

Cells turn riboflavin into two coenzymes, flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN). They carry electrons in the reactions that release energy from carbohydrate, fat and protein, and they help break down medicines, steroids and fats.

How Riboflavin Activates Other B Vitamins

Riboflavin's coenzymes are needed to turn vitamin B6 into its active form, pyridoxal 5'-phosphate, and to make niacin (B3) from the amino acid tryptophan. They also take part in folate metabolism, which keeps blood levels of homocysteine in check. So a shortage of riboflavin can lower the working forms of vitamin B6 and niacin too.

Riboflavin in Milk, Eggs, and Almonds

Three everyday foods give similar amounts. A 237 g cup of whole milk has about 0.34 mg, a 28 g handful of almonds about 0.34 mg, and one boiled egg about 0.26 mg. Each is roughly a quarter to a third of what an adult needs a day, so the three together give about three quarters of it or more.

Plants are a smaller source, with exceptions: raw mushrooms have 0.453 mg per 100 g in the Caltide food library and raw spinach 0.194 mg. In many countries breakfast cereals and bread have riboflavin added, which is why fortified cereals are left out of the ranking above.

How Light and Cooking Reduce Riboflavin

Riboflavin breaks down when exposed to light, so foods rich in it keep more of it in opaque cartons and jugs than in clear glass. It also dissolves in water: boiling loses about twice as much riboflavin into the cooking water as steaming or microwaving.

Who Is Most Likely to Be Low in Riboflavin

Because dairy and meat supply so much of it, vegans and people who eat little dairy are the most likely to fall short, along with vegetarian athletes, whose needs may be higher, and pregnant and breastfeeding women. A rare inherited condition, riboflavin transporter deficiency, blocks uptake into cells and is treated with high doses under medical care.