Vitamin B2 (Riboflavin)


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Subject: Vitamin B2 (Riboflavin)

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  • Vitamin B2, or riboflavin, is one of the water-soluble vitamins. It is synthesized in plants and microorganisms and occurs naturally in three forms: the physiologically inactive riboflavin and the physiologically active coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). The latter accounts for about 90% of the total riboflavin in whole blood. Because of their capacity to transfer electrons, FAD and FMN are essential for proton transfer in the respiratory chain, for the dehydration of fatty acids, the oxidative deamination of amino acids, and for other redox processes.

  • Normal range: 3–15 μg/L.

    • Marginally low: 2 μg/L

    • Diminished: <2 μg/L


  • Evaluation of persons who present the signs of ariboflavinosis

  • Detect riboflavin deficiency


Decreased In

  • Patients with anorexia nervosa

  • Individuals who avoid dairy products (such as people with lactose intolerance) because dairy products are a good source of riboflavin

  • Patients with malabsorptive syndromes such as celiac sprue, malignancies, and short bowel syndrome

  • Rare inborn errors of metabolism in which there is a defect in riboflavin synthesis

  • Long-term use of phenobarbital and other barbiturates, which may lead to oxidation of riboflavin and impair its function


  • Testing of nonfasting specimens or the use of dietary vitamin B2 supplementation can result in elevated plasma vitamin B2 concentrations.

  • Sample should be frozen immediately to reduce the stability of B2 in serum.

Suggested Reading

Russell  RM, Suter  PM. Vitamin and trace mineral deficiency and excess. In: Fauci  AS, Kasper  DL, Braunwald  E (eds.). Harrison's Principles of Internal Medicine, 17th ed. New York, NY: McGraw-Hill; 2008:441–449.