vitamin b2

Vitamin B2, also known as riboflavin, is a water‑soluble micronutrient belonging to the B‑vitamin complex. Chemically, riboflavin consists of an isoalloxazine ring linked to a ribitol side chain. It was first isolated in the 1930s and recognized as an essential nutrient for human health due to its unique role in cellular metabolism. In the body, riboflavin is phosphorylated to form two biologically active coenzymes: flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). These coenzyme forms are critical for the function of flavoprotein enzymes involved in oxidative reactions that oxidize carbohydrates, fats, and proteins for energy production. Riboflavin also participates in the metabolism of other vitamins; for example, the conversion of vitamin B6 to its active form and the conversion of tryptophan to niacin both require FAD and FMN. Riboflavin’s unique chemical properties as a cofactor allow it to play a central role in electron transfer reactions in the mitochondrial electron transport chain. The body cannot store large amounts of riboflavin, so a steady dietary supply is essential. Because riboflavin is water‑soluble, excess amounts are rapidly excreted in the urine, often resulting in bright yellow urine when intake is high. Unlike fat‑soluble vitamins, riboflavin does not accumulate to toxic levels under normal consumption. The discovery of riboflavin’s importance emerged from studies in the early 20th century that linked its deficiency to specific clinical syndromes affecting the skin and mucous membranes, highlighting its essential role. Modern nutritional science continues to explore riboflavin’s functions beyond basic metabolism, including roles in antioxidant mechanisms and cellular signaling pathways. Understanding the molecular basis of riboflavin’s activity has allowed clinicians to appreciate why its deficiency, though uncommon in developed nations, can disrupt multiple metabolic processes and why its adequate intake is vital for health.

Vitamin B2 (riboflavin) serves as the precursor to the coenzymes FMN and FAD, which are indispensable for energy production through the mitochondrial electron transport chain and for redox reactions throughout the body. These flavin coenzymes participate in the metabolism of carbohydrates, fats, and proteins, facilitating ATP generation—the primary energy currency of cells. Riboflavin is also integral to the metabolism of other vitamins: it supports the conversion of vitamin B6 to its active form and assists in the transformation of tryptophan into niacin. Another key function is its role in maintaining normal homocysteine levels, which, when elevated, are a risk factor for cardiovascular disease. Mechanistically, FAD and FMN act as cofactors in flavoprotein enzymes that catalyze crucial redox reactions, including the oxidation of succinate in the Krebs cycle. Emerging evidence suggests riboflavin has antioxidant properties, as it participates in the regeneration of glutathione, an endogenous antioxidant that protects cells from oxidative damage. Systematic reviews highlight riboflavin’s potential therapeutic benefits, such as its modest efficacy in migraine prophylaxis at high doses, likely due to enhanced mitochondrial energy metabolism and reduced oxidative stress. Other observational and mechanistic studies indicate riboflavin’s role in maintaining eye health and possibly lowering certain chronic disease risks, though evidence for these outcomes is still evolving. The nutrient’s involvement in multiple metabolic pathways underscores its importance for cellular function, growth, and development across all life stages, making consistent dietary intake crucial. Riboflavin’s diverse functions extend beyond energy metabolism to include support of immune function and the integrity of mucous membranes, skin, and visual system.

Daily requirements for riboflavin vary by age, sex, and physiological status. The Recommended Dietary Allowances (RDAs) established by the NIH designate specific amounts to meet the needs of nearly all healthy individuals. Infants have an Adequate Intake, while children, adolescents, and adults have RDAs ranging from 0.5 mg in toddlers to up to 1.3 mg in older teenage males and adult males. Women of childbearing age need 1.1 mg/day, which increases during pregnancy and lactation due to higher metabolic and growth demands. These RDAs ensure sufficient coenzyme formation and metabolic function under normal conditions. Factors that can increase needs include periods of rapid growth, pregnancy, lactation, chronic illness, and exposure to stressors that increase metabolic turnover. Because riboflavin is water‑soluble and not stored in significant amounts, inadequate intake over time can lead to deficiency signs, emphasizing the importance of consistent daily consumption. Dietary Guidelines emphasize obtaining nutrients primarily through a balanced diet rich in whole foods, as this approach optimizes overall nutrient status and health outcomes. Meeting riboflavin needs also supports optimal energy metabolism and metabolic flexibility. Most people consuming mixed diets that include dairy, lean meats, fish, eggs, nuts, and fortified cereals easily meet or exceed RDAs; however, individuals following restricted diets may require careful planning to ensure adequate riboflavin intake.

Riboflavin deficiency, or ariboflavinosis, manifests with distinct mucocutaneous signs due to impaired metabolic processes. Early symptoms include sore throat, cheilosis (cracks at the corners of the mouth), and glossitis (a swollen, magenta‑colored tongue). As the deficiency progresses, individuals may develop seborrheic dermatitis, characterized by red, scaly patches around the nasolabial folds, ears, and scalp. Conjunctivitis and photophobia may occur due to eye irritation, while normocytic anemia can arise from disrupted red blood cell metabolism. In severe or prolonged deficiency, impaired metabolism of other nutrients may occur, increasing susceptibility to anemia and other micronutrient deficiencies. Diagnosis often involves clinical assessment of characteristic signs, supported by laboratory measures such as decreased urinary riboflavin excretion or an elevated erythrocyte glutathione reductase activity coefficient, which reflects biochemical insufficiency. Although deficiency is uncommon in populations with fortified food supplies, certain groups remain at risk, including individuals with malabsorption disorders, chronic alcohol use, and those undergoing dialysis. Because riboflavin is essential for energy production and cellular metabolism, deficiency can also lead to nonspecific symptoms such as fatigue and impaired wound healing. Understanding these signs and identifying at‑risk populations enables early intervention and prevention of more serious outcomes.

Riboflavin is widely distributed across both animal and plant foods. Animal sources such as liver, dairy products (milk, yogurt, cheese), eggs, and lean meats are among the richest sources. Fortified breakfast cereals and grain products also provide riboflavin, especially in regions with mandatory or voluntary fortification programs. Plant‑based sources include nuts (almonds), mushrooms, green leafy vegetables, and legumes. Because riboflavin is light‑sensitive, milk is commonly packaged in opaque containers to preserve its content. Consuming a variety of these foods ensures adequate riboflavin intake and supports overall nutrient adequacy. It’s important to note that cooking methods and exposure to light can reduce riboflavin content, so proper food storage and preparation practices help preserve vitamin levels in foods. Including both animal and fortified plant sources enhances dietary diversity and nutrient intake.

Riboflavin is absorbed primarily in the proximal small intestine through a carrier‑mediated process. Once absorbed, it is phosphorylated to FMN and FAD in enterocytes and transported bound to plasma proteins. Because excess riboflavin is not stored, urinary excretion reflects recent intake and status. Factors such as gastrointestinal health and concurrent nutrient interactions can influence absorption efficiency. Certain medications and conditions that alter gut function may impair riboflavin uptake.

Most individuals meeting RDAs through diet do not require supplementation. However, supplements may be considered for individuals with restricted diets, certain medical conditions affecting absorption, or increased needs. Riboflavin supplements are available as standalone products or as part of B‑complex vitamins. High‑dose riboflavin has been studied for migraine prevention, typically at 400 mg daily, with some evidence of reduced headache frequency. As with all supplements, consult healthcare providers before use.

Riboflavin has low toxicity due to its water‑soluble nature, and no tolerable upper intake level has been established. Excess intake is excreted in urine, often causing bright yellow discoloration, a harmless sign of surplus. Very high supplemental doses are generally well‑tolerated, though occasionally gastrointestinal discomfort may occur.

Riboflavin may interact with certain medications. Long‑term use of anticonvulsants and barbiturates can increase riboflavin metabolism and reduce status. Antibiotics like tetracycline may interfere with riboflavin absorption if taken simultaneously. Other drug classes, including some antipsychotics and diuretics such as thiazides, may affect riboflavin levels or excretion. Always consult healthcare providers when combining supplements with prescription medications.

Common Forms: riboflavin tablets, B‑complex vitamins, effervescent tablets, capsules

Typical Doses: 1.1–1.6 mg daily for general needs; up to 400 mg for migraine prophylaxis under medical supervision

When to Take: With meals to enhance absorption

Best Form: riboflavin in coenzyme forms FMN/FAD

⚠️ Interactions: tetracycline antibiotics, anticonvulsants (phenytoin, phenobarbital), thiazide diuretics