Vitamin B6
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 B6?
Vitamin B6 refers to a group of six interconvertible compounds, with pyridoxal 5'-phosphate (PLP) being the most biologically active form and the primary measure of vitamin B6 status in blood tests. Vitamin B6 functions as a coenzyme in over 140 enzymatic reactions in the body, more than any other vitamin. These reactions are critical for amino acid metabolism, neurotransmitter synthesis (serotonin, dopamine, GABA, norepinephrine), hemoglobin formation, immune function, and gluconeogenesis.
Dietary sources of vitamin B6 include poultry, fish, potatoes, chickpeas, bananas, and fortified cereals. Unlike fat-soluble vitamins, B6 is water-soluble and not extensively stored in the body—approximately 80–90% of the body's B6 is found in muscle tissue bound to glycogen phosphorylase. Because of limited storage, regular dietary intake is necessary to maintain adequate levels. Vitamin B6 status is typically assessed by measuring plasma PLP levels, though functional assessments like urinary xanthurenic acid or plasma homocysteine can also provide indirect evidence of deficiency.
Por que isso importa
Vitamin B6 is essential for brain development and function, as it is required for the synthesis of key neurotransmitters including serotonin, dopamine, and GABA. Deficiency can cause peripheral neuropathy, depression, confusion, and seizures—particularly in infants. B6 also works with folate and B12 to regulate homocysteine levels; deficiency elevates homocysteine, increasing cardiovascular risk. Additionally, B6 supports immune function through its role in lymphocyte production and antibody formation. Paradoxically, excessive supplementation of B6 can cause a sensory neuropathy that mimics deficiency symptoms.
Faixas de referência normais
| Grupo | Faixa | Unidade |
|---|---|---|
| Adults (PLP) | 3.4–65.2 | ng/mL |
| Deficient | <3.4 | ng/mL |
| Marginal | 3.4–5.1 | ng/mL |
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 PLP
Causas comuns
- Excessive supplementation (typically >100 mg/day chronically)
- Megadose therapy for conditions like carpal tunnel or PMS
- Multiple supplements containing B6
Possíveis sintomas
- Sensory peripheral neuropathy (numbness, tingling in hands and feet)
- Difficulty walking and loss of coordination (ataxia)
- Photosensitivity
- Nausea and heartburn
- Painful skin lesions
O que fazer: Discontinue B6 supplementation immediately. B6 toxicity typically occurs with chronic intake above 100 mg/day, though some individuals may be sensitive to lower doses. Symptoms usually improve within weeks to months after stopping supplementation, though severe neuropathy can be slow to resolve or occasionally permanent. The upper limit is 100 mg/day for adults. Review all supplements for hidden B6 content.
O que significam níveis baixos de PLP
Causas comuns
- Inadequate dietary intake
- Chronic alcohol use
- Medications (isoniazid, hydralazine, penicillamine, oral contraceptives)
- Malabsorption disorders
- Kidney disease (dialysis increases losses)
- Autoimmune conditions
- Pregnancy (increased demand)
Possíveis sintomas
- Peripheral neuropathy (numbness and tingling)
- Dermatitis and cracked lips (cheilosis)
- Glossitis (swollen, sore tongue)
- Depression and confusion
- Weakened immune response
- Microcytic anemia (similar to iron deficiency)
- Seizures in severe deficiency (especially in infants)
O que fazer: Treat underlying causes and supplement with pyridoxine, typically 25–50 mg daily for mild deficiency. Patients on isoniazid should receive prophylactic B6 (25–50 mg daily). Increase dietary sources including poultry, fish, potatoes, and bananas. If on medications that deplete B6, discuss ongoing supplementation with your doctor. Recheck levels after 4–6 weeks of supplementation.
Quando o exame de PLP é recomendado?
- When peripheral neuropathy of unknown cause is present
- In patients on medications known to deplete B6 (isoniazid, hydralazine)
- When unexplained anemia does not respond to iron therapy
- If elevated homocysteine levels are found
- In chronic alcohol use or malnutrition
- When B6 toxicity from over-supplementation is suspected
Perguntas frequentes
Biomarcadores relacionados
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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.