Riboflavin, also known as vitamin B-2, is a water-soluble vitamin that promotes normal growth, facilitates the breakdown of fat, and aids the syntheses of steroids, red blood cells, and glycogen. Natural sources of vitamin B-2 include almonds, yeast, cheese, eggs, chicken, beef, organ meats, and wheat germ.

View a second image of riboflavin.

Synthesized riboflavin is available as a dietary supplement or is found in vitamin-enriched foods, such as skim milk and breakfast cereals, and is featured in animal feeds. Activation of vitamin B-6 and folic acid require riboflavin, and the vitamin is helpful in the treatment of cataracts and other eye disorders. Symptoms associated with riboflavin deficiency are inflammation of the tongue, light sensitivity, itching, dizziness, insomnia, and slow learning.

Named from the Latin word flavius (yellow) to denote the rich color of crystals formed from the pure vitamin and the deep yellow color it gives to urine, riboflavin was formerly known also as lactoflavin or vitamin G. Biochemically, riboflavin is metabolized to form the flavin coenzymes: flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN). The functional moiety in both coenzymes is riboflavin's isoalloxazine ring system, which serves as a two-electron acceptor in enzymatic biochemical reductions. Enzymes that use a flavin cofactor are termed "flavoproteins" and have been extensively studied.

On an industrial scale, riboflavin is manufactured via biosynthesis using yeast or other fermenting organisms, and it is used as a yellow coloring agent and for vitamin fortification of foods such as cereals, sauces, vitamin supplements, and soups. However, it is difficult to incorporate into most food products because of it insolubility in water and thus, the more expensive, but water-soluble derivative, riboflavin-5'-phosphate is often used in milk products, jams, and sugar products. Upon ingestion, this chemically prepared supplement and dye converts to free riboflavin.