A nutrient in the vitamin B complex that the body needs in small amounts to function and stay healthy. Riboflavin helps make red blood cells, helps some enzymes work properly, and keeps skin, nails, and hair healthy. It is found in milk, eggs, malted barley, organ meats, yeast, and leafy vegetables. Riboflavin is water-soluble (can dissolve in water) and must be taken in every day. Not enough riboflavin can cause anemia (a low number of red blood cells), mouth sores, and skin problems. Amounts of riboflavin may be higher in the blood of patients with some types of cancer. Also called vitamin B2.