Vitamins

Riboflavin (Vitamin B2)

By All The Nutrients Editorial Team Published: 7 min read

Riboflavin (vitamin B2) is a water-soluble B-vitamin that forms the core of two coenzymes — flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) — that are essential components of hundreds of oxidation-reduction reactions in cellular energy metabolism, fatty acid β-oxidation, amino acid catabolism, and the electron transport chain. Riboflavin is also required for converting other B-vitamins (B6, folate, niacin) to their active coenzyme forms, making its adequacy a prerequisite for the function of the entire B-vitamin network. The richest dietary sources are organ meats, dairy products, eggs, fortified grains, and almonds.

Daily Value

1.30 mg

FDA 2020

Top Source

Yeast extract spread

17.5 mg

What Does Riboflavin (Vitamin B2) Do?

  • Energy metabolism via FAD and FMN: FAD is a critical electron carrier in the mitochondrial electron transport chain (Complex I, Complex II) and in fatty acid β-oxidation. FMN is the cofactor for Complex I (NADH-ubiquinone oxidoreductase) — the entry point for electrons from NADH into the chain. Without riboflavin, the electron transport chain cannot run efficiently, and ATP production from all macronutrient fuels is impaired.
  • Glutathione regeneration and antioxidant defence: Glutathione reductase — a FAD-dependent enzyme — regenerates oxidised glutathione (GSSG) back to its reduced, active antioxidant form (GSH). This makes riboflavin essential for maintaining the cellular glutathione pool, which is the primary water-soluble antioxidant system protecting cells from oxidative damage. Erythrocyte glutathione reductase activity coefficient (EGRac) is the standard functional biomarker of riboflavin status.
  • B-vitamin network activation: Riboflavin is required for converting other B-vitamins to their active coenzyme forms: it converts B6 (pyridoxine) to pyridoxal-5-phosphate (PLP) via FAD-dependent pyridoxine-phosphate oxidase; it supports folate conversion to its active tetrahydrofolate forms; and it is a cofactor in the tryptophan→niacin conversion pathway. This makes riboflavin deficiency multiplicative — it produces functional deficiencies in B6, folate, and niacin simultaneously.
  • Iron metabolism and anaemia prevention: FAD-dependent enzymes are required for mobilising iron from body stores (ferritin) and incorporating it into haemoglobin. Riboflavin deficiency impairs intestinal iron absorption and mobilisation, causing anaemia that does not respond to iron supplementation alone. This interaction is particularly clinically important in populations with both riboflavin inadequacy and iron deficiency — common in sub-Saharan Africa and South Asia.
  • Migraine prevention (clinical use): High-dose riboflavin (400 mg/day) significantly reduces migraine frequency and severity in a proportion of patients. The proposed mechanism is correction of mitochondrial energy deficiency in migraine-prone neurons — riboflavin (as FAD in Complex I) enhances mitochondrial electron transport efficiency. Multiple RCTs have shown 50%+ reduction in migraine days with 400 mg riboflavin, with an excellent safety profile given that excess riboflavin is simply excreted in urine (producing bright yellow urine).
Horizontal bar chart of riboflavin per 100g: lamb kidney 3.34mg, beef liver 2.97mg, chicken liver 2.35mg, almonds 1.14mg, portobello mushrooms 0.49mg, eggs 0.46mg, cheddar cheese 0.34mg, milk (per 100mL) 0.18mg. FDA DV reference line at 1.3mg.
Organ meats lead by a wide margin. For everyday eating, eggs, dairy, almonds, and mushrooms are the most practical riboflavin sources.
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Signs of Riboflavin (Vitamin B2) Deficiency

Riboflavin deficiency (ariboflavinosis) is rarely severe enough to produce dramatic clinical disease in isolation because cells conserve FAD during depletion. However, subclinical deficiency producing the following cluster of mucocutaneous and haematological signs is common in populations with low dairy intake and low fortified grain consumption:

  • Cheilosis — cracks at the corners of the mouth (angular stomatitis) and vertical fissures on the lips; often painful and prone to secondary infection; the most characteristic riboflavin deficiency sign
  • Glossitis — magenta (purplish-red) discolouration and inflammation of the tongue; papillae atrophy making the tongue appear smooth
  • Seborrhoeic dermatitis — greasy, scaly dermatitis around the nose, mouth, and ears; resembles psoriasis
  • Corneal vascularisation — growth of capillaries into the normally avascular cornea; can impair vision in severe deficiency; associated with the high riboflavin content of the lens and cornea
  • Anaemia — normocytic (normal cell size), normochromic anaemia from impaired erythropoiesis and iron mobilisation; does not respond to iron supplementation without correcting riboflavin
  • Neurological symptoms in severe deficiency — peripheral neuropathy, ataxia; rare in isolation; usually co-occurs with other B-vitamin deficiencies

Consider supplementing

B-Complex supplement

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How to Get the Most from Riboflavin (Vitamin B2)

Riboflavin absorption is carrier-mediated in the small intestine and is generally efficient (about 60–65% of dietary riboflavin is absorbed), though it can be limited by dose and food matrix:

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Take riboflavin supplements with food

Intestinal absorption of riboflavin is saturated at about 27 mg per dose — any excess is excreted unchanged in urine (producing bright yellow urine, which is harmless). Absorption is enhanced when taken with food, as food slows gastric emptying and prolongs contact with intestinal transporters. For the standard dietary context, this is not a concern; it matters mainly for the 400 mg/day doses used in migraine prophylaxis.

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Protect dairy and riboflavin-rich foods from light

Riboflavin is highly photosensitive — it degrades rapidly when exposed to UV or visible light. Milk left in clear glass bottles or exposed to fluorescent light for 2 hours loses 50%+ of its riboflavin content. This is why milk is sold in opaque cartons or cardboard in most countries. Store riboflavin-rich foods (milk, yoghurt, eggs) in light-blocking containers and away from direct sunlight.

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Pregnant and breastfeeding women have increased needs

The RDA increases to 1.4 mg/day during pregnancy and 1.6 mg/day during breastfeeding — a 27–45% increase above the baseline 1.1 mg/day for adult women. Riboflavin is actively transferred into breast milk, and the infant's entire supply comes from the mother. Dairy products, eggs, and fortified grains are the most reliable sources to meet increased needs.

Common Riboflavin (Vitamin B2) Questions

How much riboflavin do I need per day?

The FDA Daily Value for riboflavin is 1.3 mg/day. The National Academies RDA is 1.3 mg/day for adult men and 1.1 mg/day for adult women 19+; 1.4 mg/day during pregnancy; 1.6 mg/day while breastfeeding. No Tolerable Upper Intake Level has been established for riboflavin from food or supplements — no adverse effects have been documented at any intake level because excess riboflavin is readily excreted in urine. Most adults in developed countries meet the RDA through dairy products and fortified grain products.

What foods are highest in riboflavin?

Per 100 g: beef liver (2.97 mg), lamb kidney (3.34 mg), chicken liver (2.35 mg), marmite/yeast extract (11 mg — used in small amounts), almonds (1.14 mg), milk (0.18 mg per 100 mL / 0.45 mg per 240 mL glass), yoghurt plain (0.26 mg per 100 g), eggs (0.46 mg per 100 g / 0.23 mg per large egg), cheddar cheese (0.34 mg), fortified breakfast cereals (up to 1.7 mg per serving), portobello mushrooms (0.49 mg per 100 g). A glass of milk, an egg, and a serving of fortified cereal together cover more than the full daily value.

Can riboflavin prevent migraines?

Yes — at high doses (400 mg/day), riboflavin is an evidence-based migraine prophylaxis option. A landmark 1998 RCT (Schoenen et al., Neurology) found that 400 mg/day reduced attack frequency by 50% in 59% of patients versus 15% in the placebo group over 3 months. The ECAM (European College of Headache) guidelines include high-dose riboflavin as a first-line preventive for migraine. Its advantages: excellent safety profile, very low cost, and no drug interactions. The main side effect is bright yellow-orange urine (harmless). The effective dose (400 mg) is about 300× the RDA and must be taken as a supplement — dietary sources cannot provide this dose.

Why is my urine bright yellow after taking B-vitamins?

The vivid yellow-orange colour in urine after taking multivitamins or B-complex supplements is almost entirely due to excess riboflavin (vitamin B2) being excreted. Riboflavin has an intensely yellow-green fluorescent colour — in fact, the name "riboflavin" derives from the Latin "flavus" (yellow). Because riboflavin absorption is dose-limited and any excess above cellular needs is immediately excreted by the kidneys, the colour of urine changes within 1–2 hours of a supplement dose. This is completely harmless and simply indicates that the dose exceeded the body's immediate riboflavin needs. Urine returns to its normal colour within a few hours.

Are vegans at risk of riboflavin deficiency?

Riboflavin deficiency is a genuine concern for vegans not eating fortified foods, because the primary dietary sources in most diets — dairy and eggs — are excluded. Studies of strict vegans in some regions show marginal riboflavin status, particularly in countries where grains are not fortified. However, plant-based diets that include regular portions of nutritional yeast (very rich in riboflavin, often fortified), almonds, mushrooms (especially UV-exposed), fortified plant milks, fortified cereals, sunflower seeds, edamame, and green leafy vegetables can meet the RDA. Reading food labels and choosing fortified alternatives to dairy is the most practical strategy.