Vitamin B2 (Riboflavin)
Vitaminas e mineraisÚltima revisão: 7 de abril de 2026. Abordagem de fontes: contexto padrão de interpretação laboratorial, material médico de referência e orientações clínicas ou de saúde pública quando relevantes.
O que é Vitamin B2 (Riboflavin)?
Riboflavin, also known as vitamin B2, is a water-soluble vitamin that serves as a precursor to two essential coenzymes: flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). These coenzymes participate in over 100 enzymatic reactions throughout the body, playing central roles in energy production, cellular respiration, and the metabolism of fats, carbohydrates, and proteins. FAD is also a critical cofactor for the enzyme methylenetetrahydrofolate reductase (MTHFR), linking riboflavin status to folate and homocysteine metabolism.
Riboflavin is obtained primarily from dietary sources including dairy products, eggs, lean meats, organ meats, green vegetables, and fortified cereals. Because it is water-soluble, the body has limited storage capacity and requires consistent dietary intake. Riboflavin status is most accurately assessed by measuring erythrocyte glutathione reductase activity coefficient (EGRAC) or directly measuring plasma/serum riboflavin levels. Clinical deficiency, known as ariboflavinosis, often coexists with other B-vitamin deficiencies and is more common in populations with limited access to dairy and animal products.
Por que isso importa
Riboflavin is fundamental to energy metabolism—without adequate B2, the body cannot efficiently convert food into usable energy. As a precursor to FAD, riboflavin supports the electron transport chain in mitochondria, the antioxidant glutathione system, and the metabolism of other B vitamins including folate, niacin, and vitamin B6. Deficiency can impair iron absorption and utilization, contribute to anemia, and elevate homocysteine levels. Emerging evidence also suggests riboflavin supplementation may reduce migraine frequency in some patients.
Faixas de referência normais
| Grupo | Faixa | Unidade |
|---|---|---|
| Adults (serum) | 6.2–39.0 | nmol/L |
| Adults (EGRAC) | <1.4 | ratio |
As faixas de referência podem variar entre laboratórios. Sempre compare seus resultados com as faixas fornecidas pelo seu local de exame.
O que significam níveis altos de B2
Causas comuns
- Excessive supplementation (generally well-tolerated)
- High dietary intake of fortified foods
- Parenteral nutrition with riboflavin
Possíveis sintomas
- Usually asymptomatic—excess is excreted in urine (causing bright yellow color)
- No established toxicity from oral intake
- Possible photosensitivity at very high doses
O que fazer: High riboflavin levels are not considered harmful, as excess is rapidly excreted by the kidneys, producing characteristically bright yellow urine. No upper tolerable intake level has been established due to the lack of observed toxicity. If levels are excessively high, simply reduce supplementation. The bright yellow urine caused by riboflavin is harmless and is not a cause for concern.
O que significam níveis baixos de B2
Causas comuns
- Inadequate dietary intake (common in vegans and those avoiding dairy)
- Chronic alcoholism (impairs absorption and increases excretion)
- Malabsorption disorders (celiac disease, inflammatory bowel disease)
- Medications (certain antidepressants, antimalarials, phenobarbital)
- Hypothyroidism and adrenal insufficiency
- Increased requirements during pregnancy and lactation
Possíveis sintomas
- Angular cheilitis (cracking at corners of the mouth)
- Glossitis (swollen, magenta-colored tongue)
- Sore throat and mucosal inflammation
- Seborrheic dermatitis-like skin rash
- Eye symptoms: photophobia, tearing, burning, itching
- Normochromic normocytic anemia
- Fatigue and weakness
O que fazer: Riboflavin deficiency is treated with supplementation, typically 5–30 mg daily until symptoms resolve, then a maintenance dose of 1–4 mg daily. Increase dietary intake of riboflavin-rich foods including milk, yogurt, eggs, almonds, and fortified grains. Because riboflavin deficiency rarely occurs in isolation, your doctor should assess other B-vitamin levels (B6, B12, niacin, folate). Address underlying causes such as malabsorption or alcoholism.
Quando o exame de B2 é recomendado?
- When angular cheilitis or glossitis is present without clear cause
- In patients with chronic alcoholism or malabsorption disorders
- When evaluating multiple B-vitamin deficiencies
- During pregnancy or lactation if dietary intake is poor
- When elevated homocysteine persists despite folate and B12 supplementation
- In patients on long-term medications that interfere with riboflavin
Perguntas frequentes
Biomarcadores relacionados
Leitura relacionada
Condições
Referências e abordagem de revisão
As páginas do glossário de biomarcadores são explicações educativas e devem ser interpretadas junto com as faixas de referência e observações fornecidas pelo seu laboratório e pelo seu médico. Para conhecer nossos padrões editoriais e processo de revisão, veja nossa Política editorial e a nossa revisão de conteúdo.
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Enviar resultados de exames →Aviso médico: Estas informações são apenas educativas e não substituem orientação, diagnóstico ou tratamento médico profissional. As faixas de referência podem variar entre laboratórios. Sempre converse com seu profissional de saúde sobre a interpretação dos seus resultados específicos.