Flavins are critical for the metabolism of carbohydrates, fats, and proteins. The glutathione redox cycle plays a major role in protecting organisms from reactive oxygen species , such as hydroperoxides. See diagram . Glutathione reductase requires FAD to regenerate two molecules of reduced glutathione from oxidized glutathione. Xanthine oxidase , another FAD-dependent enzyme, catalyzes the oxidation of hypoxanthine and xanthine to uric acid.
Uric acid is one of the most effective water-soluble antioxidants in the blood.
Riboflavin deficiency alters iron metabolism. In humans, improving riboflavin nutritional status has been found to increase circulating hemoglobin levels. Alcoholics are at increased risk for riboflavin deficiency due to decreased intake, decreased absorption, and impaired utilization of riboflavin. Anorexic individuals rarely consume adequate riboflavin. Lactose intolerance may prevent people from consuming milk or dairy products, which are good sources of riboflavin.