Clinical Information

Riboflavin, which is commonly known as vitamin B2, is a water-soluble vitamin that is the precursor to the coenzymes flavin mononucleotide and flavin adenine dinucleotide. These coenzymes play a pivot role in a plethora of oxidation-reduction reactions, energy production, and metabolism of fats, drugs, and steroids.

Deficiency of riboflavin (ariboflavinosis) is characterized by sore throat, cheilosis (lesions on the lips), angular stomatitis (lesions on the angles of the mouth), glossitis (fissured and magenta-colored tongue), corneal vascularization, dyssebacia (red, scaly, greasy patches on the nose, eyelids, scrotum, and labia), and normocytic, normochromic anemia associated with pure red blood cell aplasia of the bone marrow. Riboflavin coenzymes play a key role in metabolism of vitamin B9 and vitamin B12, the activation of vitamin B6, and the conversion of tryptophan to vitamin B3. Therefore, deficiency of vitamin B2 can cause issues associated with other B vitamins as well. Early-stage symptoms of deficiency typically respond well to supplementation, but later stage anatomical changes cannot be reversed with therapy alone. Those at risk for vitamin B2 deficiency include those that are malnourished, vegan or vegetarian, individuals with hypothyroidism or adrenal insufficiency, pregnant and lactating women and their infants, and those on drugs with similar chemical structures such as tricyclic antidepressants.

In addition to dietary deficiency, there are rare inborn errors of metabolism, primarily involving loss of function of riboflavin transporters, which result in functional vitamin B2 deficiency. Many of these cases present with neurodegenerative features and/or hearing loss, which if left untreated can be fatal. In these cases, high-dose riboflavin supplementation is critical.

Riboflavin has a low level of toxicity and no case of riboflavin toxicity in humans has been reported. The limited absorptivity of riboflavin and its ready excretion in the urine normally precludes a health problem due to increased intake of riboflavin.