Vitamin B2 (Riboflavin) is an orange-yellow crystal. B2 is stable to heat, acid, and oxidation. It is, however, sensitive to light, especially ultraviolet light, as in sunlight. So foods containing even moderate amounts of riboflavin (for example, milk) need to be protected from sunlight. Only a little of the B2 in foods is lost in the cooking water.

Riboflavin acts as an intermediary in the transfer of electrons in numerous essential oxidation-reduction reactions and participates in many metabolic reactions of carbohydrates, fats, and protein. Riboflavin is necessary for cell respiration. It works with enzymes in the utilization of cell oxygen. Riboflavin is easily absorbed through the walls of the small intestine where it is carried by the blood to the tissues of the body, used, and then excess is excreted in the urine. Riboflavin coenzymes are essential for the conversion of pyridoxine (vitamin B6) and folic acid into their coenzyme forms and for the transformation of tryptophan into niacin. Riboflavin is not stored in great quantity, thus must be supplied regularly. Riboflavin is necessary for the maintenance of good vision, skin, nails, and hair. It helps to prevent cancer and helps release energy from food. Riboflavin also helps maintain healthy respiratory, the nervous system, digestive and circulatory mucous membrane linings. Riboflavin promotes normal growth and development.

Excess B2 is eliminated in the urine, which can give it a yellow-green fluorescent glow, commonly seen after taking B complex supplements. Riboflavin is not stored in the body, except for a small quantity in the liver and kidneys, so it is needed regularly in the diet.

It is required by the body to use oxygen and the metabolism of amino acids, fatty acids, and carbohydrates. Riboflavin is further needed to activate vitamin B6 (pyridoxine), helps to create niacin and assists the adrenal gland. It may be used for red blood cell formation, antibody production, cell respiration, and growth. It eases watery eye fatigue and may be helpful in the prevention and treatment of cataracts. Vitamin B2 is required for the health of the mucus membranes in the digestive tract and helps with the absorption of iron and vitamin B6. Although it is needed for periods of rapid growth, it is also needed when protein intake is high, and is most beneficial to the skin, hair and nails.

A shortage of this vitamin may manifest itself as cracks and sores at the corners of the mouth, eye disorders, inflammation of the mouth and tongue, and skin lesions. Dermatitis, dizziness, hair loss, insomnia, light sensitivity, poor digestion, retarded growth, and slow mental responses have also been reported. Burning feet can also be indicative of a shortage.

The limited capacity to absorb orally administered riboflavin precludes its potential for harm. Riboflavin intake of many times the RDA is without demonstrable toxicity. A normal yellow discoloration of the urine is seen with an increased intake of this vitamin but it is normal and harmless.

Extra might be needed when consuming alcohol, antibiotics, and birth control pills or doing strenuous exercise. If you are under a lot of stress or on a calorie-restricted diet, this vitamin could also be of use.

Organ meats, nuts, cheese, eggs, milk and lean meat are great sources of riboflavin, but is also available in good quantities in green leafy vegetables, fish, legumes, whole grains, and yogurt.