Vitamin B2, also known as riboflavin, is a water-soluble B vitamin essential for cellular energy production. The body cannot synthesize riboflavin and must obtain it from foods like dairy, eggs, meats, and green vegetables. Once absorbed, riboflavin is converted into its active forms, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). These coenzymes are crucial for oxidation–reduction reactions that drive mitochondrial energy production, metabolize carbohydrates, fats, and proteins, and support antioxidant defenses. Adequate riboflavin ensures efficient ATP generation, redox balance, and activation of other vitamins, making it vital for overall metabolic health.

Early signs of riboflavin deficiency include cracks at the corners of the mouth (angular cheilitis), a sore or swollen tongue, scaly facial rash, light sensitivity, red or irritated eyes, and unexplained fatigue. In more severe cases, deficiency can lead to anemia due to impaired iron utilization, slowed growth in children, and disproportionate fatigue in teens. Women who are pregnant or taking oral contraceptives, as well as individuals with malabsorption, alcoholism, or restrictive diets, are at higher risk. If you experience these symptoms, consider checking your riboflavin status through lab testing.

Vitamin B2 is found in a variety of foods, including dairy products (milk, cheese, yogurt), eggs, lean meats, green vegetables (such as spinach and broccoli), and fortified grains or cereals. Because the body cannot store large amounts of riboflavin, regular intake from these foods is necessary to maintain adequate levels. People with restricted diets, malabsorption issues, or increased needs (such as during pregnancy) may require supplementation to prevent deficiency.

Riboflavin status can be assessed through blood or urine measurements of riboflavin, FMN, or FAD, or by functional enzyme-based tests like the erythrocyte glutathione reductase activation coefficient. Reference ranges vary, but optimal status is typically indicated by mid-range values where flavoprotein enzymes are saturated and stable. Low values suggest deficiency, while very high values often reflect recent intake rather than tissue sufficiency. Interpretation should consider related markers such as folate, B12, homocysteine, CBC, and ferritin, as well as clinical symptoms.

Low riboflavin impairs the body’s ability to produce energy, leading to symptoms like tiredness, reduced exercise tolerance, mouth and skin irritation, and anemia. It can also increase oxidative stress, hinder the activation of other B vitamins (B6, folate), and raise homocysteine levels, which is linked to cardiovascular risk. In pregnancy, deficiency may worsen anemia and increase the risk of high blood pressure, especially in those with MTHFR gene variants. Children may experience slowed growth, and older adults or those with chronic illness are more susceptible to deficiency.

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Riboflavin, through its coenzyme forms FMN and FAD, is required to activate other B vitamins, including vitamin B6 (pyridoxal 5′-phosphate) and folate. It is also a cofactor for the MTHFR enzyme, which is critical for converting homocysteine to methionine. Low riboflavin can impair these processes, leading to elevated homocysteine levels—a risk factor for cardiovascular disease and complications in pregnancy. Individuals with MTHFR gene variants may have higher riboflavin needs to maintain healthy homocysteine metabolism.

High riboflavin levels in blood or urine are usually due to recent intake from supplements or fortified foods. Because riboflavin is water-soluble, excess amounts are typically excreted in urine, often turning it bright yellow. Persistently high levels without recent intake may indicate reduced kidney clearance or timing effects, but toxicity is rare. There is no evidence that high riboflavin intake from food or supplements causes harm in healthy individuals, as the body efficiently eliminates excess.

Individuals at higher risk for riboflavin deficiency include those with malabsorption syndromes (such as after bariatric surgery), chronic alcoholism, restrictive diets, older adults, pregnant women, and those taking oral contraceptives. Increased needs during growth, pregnancy, or chronic illness can also raise risk. These groups may have reduced intake, impaired absorption, or higher requirements, making regular monitoring and dietary support important for maintaining adequate riboflavin status.

Riboflavin deficiency can be corrected by increasing dietary intake of riboflavin-rich foods or using targeted supplements. Addressing underlying causes such as malabsorption, restrictive diets, or increased physiological needs is crucial. Monitoring riboflavin status alongside related markers (folate, B12, homocysteine, CBC, ferritin) helps guide effective intervention. For those at risk, regular consumption of dairy, eggs, meats, green vegetables, and fortified grains, or appropriate supplementation, can help restore and maintain optimal energy, redox balance, and overall health.