Vitamin B2 (riboflavin)
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Water-soluble and like other B-vitamins, it is not appreciably stored and therefore must be supplied daily; facilitates the metabolism of carbohydrates, fats and proteins; combines with phosphoric acid to become part of two important flavin co-enzymes: FAD (flavin adenine dinucleotide) and FMN (flavin mononucleotide); FAD and FMN are known to bind to over 100 flavoprotein enzymes which catalyse oxidation-reduction reactions in cells. These enzymes include the oxidases which function aerobically, and dehydrogenases which function anaeobically; plays a critical role in the conversion of carbohydrates to ATP in the production of energy; in energy production, flavoprotein enzymes function as hydrogen carriers in the electron transport system resulting in the production of ATP and energy within the mitochondria; has important antioxidant activity, both by itself and as part of the enzyme glutathione peroxidase; necessary for growth and reproduction; and necessary for the healthy growth of hair, nails and skin.

A vitamin B2 deficiency could be a contributing cause of acne, angular stomatitis, blood-shot eyes and an extreme sensitivity to light, burning, itching, reddening and tearing of the eyes; cataracts, chelosis (cracks in the corners of the mouth), chronic diarrhea, compromised immune function, dementia, eyes that tire easily; excessive stress, muscle cramp, sebborheic dermatitis (dry, itchy scaly skin) and scaling eczema of the face and genitals may develop, slow wound healing, and soreness and burning of the lips, mouth and tongue (possible magenta-colored tongue). A vitamin B2 deficiency frequently overlaps with deficiencies of vitamin B3, vitamin B6 and/or iron, and a severe deficiency can also cause depression and hysteria.

Pharmaceutical drugs that can cause a vitamin B2 deficiency include acetophenazine, aminoglycosides, amitriptyline, amoxapine, cephalosporins, chlorpromazine, chlortetracycline, clomipramine, demeclocycline, desipramine, doxepin, doxycycline, fluoroquinolones, fluphenazine, imipramine, macrolides, mesoiradazine, methdiazine, methotrimeprazine, minocycline, nortriptyline, oral contraceptives, oxytetracycline, penicillins, perphenazine, prochlorperazine, promazine, promethazine, protriptyline, sulfonamides, tetracyclines, thiethylperazine, thioridazine, trifluoperazine, trimethoprim and trimipramine.

Dietary sources richest in vitamin B2 (per serving) include avocado, egg, dark green leafy vegetables, enriched grains and grain products, fish (especially salmon and tuna), liver, meats, milk and dairy products, nutritional supplements, nutritional yeasts and oyster. Vitamin B2 is absorbed from the upper part of the small intestine and thus, when repleting the diet with a nutritional supplement, it is best absorbed when taken with food. In addition, vitamin B2 is heat stable but very sensitive to destruction by light. Because it is water-soluble, substantial amounts are lost by leaching into water when cooking. Since B-2 exists in the germ and bran of grains, milling and processing of grains results in substantial losses.