Vitamin B2

• Active forms: flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD)
  • Active forms of riboFlavin are FMN and FAD.
• Sources: meat, fish, eggs, milk, green vegetables, yeast

Functions

FAD and FMN are cofactors for enzymes that are involved in redox reactions (chemical reactions in which electrons are transferred from one substance to another), including:

• Succinate dehydrogenase (TCA cycle)
• FAD is part of glutathione reductase (GR) in erythrocytes: NADPH binds to GR → reduction of FAD to FADH- → FADH- breaks disulfide bond in GSSG → GSR can be reduced

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Vitamin B2 deficiency

• Etiology
  • Dietary inadequacy: Most common cause, especially in individuals with diets low in meat and dairy products.
  • Malabsorption syndromes: Conditions like celiac disease or short bowel syndrome can impair absorption.
  • Chronic alcoholism: A frequent cause of multiple B-vitamin deficiencies, including B₂.
  • Increased requirements: Pregnancy, lactation, and periods of rapid growth can increase the need for riboflavin.
  • Phototherapy: Used for hyperbilirubinemia in newborns, as riboflavin is light-sensitive and can be degraded.
• Clinical Presentation (Ariboflavinosis)
  • The classic triad is often remembered by the “2 C’s”:
    • Cheilosis: Fissures and scaling at the corners of the mouth (angular stomatitis).
    • Corneal vascularization: Growth of new blood vessels into the cornea, which can cause light sensitivity and blurry vision.
  • Other findings:
    • Glossitis: Inflammation of the tongue, giving it a characteristic magenta color.
    • Seborrheic dermatitis: Oily, scaly rash typically affecting nasolabial folds, scrotum, or vulva.
    • Normochromic, normocytic anemia.
• Diagnosis
  • The diagnosis is primarily clinical, based on the characteristic signs and symptoms.
  • A therapeutic trial of riboflavin supplementation leading to the resolution of symptoms can confirm the diagnosis.
  • Lab tests, such as measuring erythrocyte glutathione reductase activity or urinary riboflavin excretion, can be used but are less common in clinical practice.
  • It’s important to note that isolated riboflavin deficiency is rare; it often occurs with other B-vitamin deficiencies.