Ascorbate

Vitamin C

Q: Can vitamin C prevent or cure the common cold?

Research shows that regular vitamin C supplementation does not prevent colds in the general population, but it may modestly reduce cold duration by about 8% in adults (roughly half a day shorter). However, in people under extreme physical stress (marathon runners, soldiers), regular vitamin C supplementation can reduce cold incidence by up to 50%. Taking vitamin C after cold symptoms begin has little to no effect on duration or severity. A balanced diet with adequate vitamin C is the best approach for immune support.

Q: Why do smokers need more vitamin C?

Smoking generates enormous amounts of free radicals and oxidative stress, which rapidly deplete vitamin C stores. Smokers have 25–40% lower plasma vitamin C levels than non-smokers, even with similar dietary intake. The increased oxidative burden means smokers metabolize vitamin C faster and require approximately 35 mg more per day than non-smokers. Secondhand smoke exposure also increases vitamin C requirements, though to a lesser degree.

Q: Can high-dose vitamin C cause kidney stones?

Yes, high-dose vitamin C (typically above 1,000–2,000 mg/day) can increase urinary oxalate excretion, which may raise the risk of calcium oxalate kidney stones in susceptible individuals—particularly those with a history of stones or kidney disease. The body converts some excess vitamin C to oxalate, which can crystallize in the urinary tract. People at risk of kidney stones should limit vitamin C supplements to standard recommended amounts and stay well hydrated.

Vitaminas e minerais

Última 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 C?

Vitamin C (ascorbic acid) is a water-soluble vitamin and potent antioxidant that plays essential roles in collagen synthesis, immune defense, iron absorption, and protection against oxidative stress. Humans are among the few mammals that cannot synthesize vitamin C internally due to a mutation in the gene encoding L-gulonolactone oxidase, making dietary intake absolutely essential. The body maintains a total pool of approximately 1,500–2,000 mg of vitamin C, with the highest concentrations found in the adrenal glands, pituitary gland, white blood cells, and eyes.

Vitamin C is absorbed in the small intestine via sodium-dependent active transport, with absorption efficiency decreasing as intake increases—approximately 70–90% at moderate doses (30–180 mg/day) but dropping below 50% at doses exceeding 1,000 mg. Excess vitamin C is excreted by the kidneys. Blood levels are measured as plasma or serum ascorbic acid concentration and reflect recent dietary intake over the preceding 1–2 weeks. Vitamin C's role as an electron donor underlies its antioxidant properties and its ability to regenerate other antioxidants like vitamin E.

Por que isso importa

Vitamin C is critical for collagen production—the structural protein in skin, blood vessels, tendons, and bones. Severe deficiency causes scurvy, a potentially fatal disease characterized by bleeding gums, tooth loss, impaired wound healing, and hemorrhage. Even subclinical deficiency impairs immune function, slows wound healing, and increases susceptibility to infections. Vitamin C enhances the absorption of non-heme iron from plant sources by 2–3 fold, making it important for preventing iron deficiency anemia. As an antioxidant, it protects cells from free radical damage associated with chronic diseases, aging, and environmental pollutants.

Faixas de referência normais

Grupo	Faixa	Unidade
Adults	0.4–1.5	mg/dL
Deficient	<0.2	mg/dL
Scurvy risk	<0.1	mg/dL

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 Ascorbate

Causas comuns

High-dose vitamin C supplementation
Excessive dietary intake (uncommon)

Possíveis sintomas

Diarrhea and abdominal cramps
Nausea
Kidney stones (in susceptible individuals)
False-positive or false-negative results on certain lab tests (glucose, occult blood)

O que fazer: Reduce vitamin C supplementation to recommended daily amounts (75–90 mg for adults). High-dose vitamin C can increase oxalate excretion, raising kidney stone risk in susceptible individuals. Inform your doctor about supplement use, as high vitamin C can interfere with certain laboratory tests. Very high doses should be avoided in patients with kidney disease, hemochromatosis, or G6PD deficiency.

O que significam níveis baixos de Ascorbate

Causas comuns

Inadequate fruit and vegetable intake
Smoking (increases vitamin C turnover by 30–40%)
Chronic alcohol use
Malabsorption disorders
Dialysis
Restrictive diets or eating disorders
Older age with limited dietary variety

Possíveis sintomas

Fatigue and malaise
Bleeding gums and loose teeth
Easy bruising and petechiae
Poor wound healing
Joint pain and swelling
Dry, rough skin and corkscrew hairs
Iron deficiency anemia (impaired iron absorption)
Depression and irritability

O que fazer: Increase dietary vitamin C through citrus fruits, strawberries, bell peppers, broccoli, and tomatoes. For diagnosed deficiency, supplement with 250–500 mg of vitamin C twice daily until levels normalize, then maintain adequate dietary intake. Smokers should aim for an additional 35 mg/day above the standard recommendation. Scurvy requires higher doses and medical monitoring, with symptoms typically improving within days to weeks of treatment.

Quando o exame de Ascorbate é recomendado?

When scurvy is suspected (bleeding gums, poor wound healing)
In malnourished patients or those with restrictive diets
Smokers with symptoms of deficiency
When unexplained fatigue or bleeding occurs
In elderly patients with limited dietary variety
In patients with chronic malabsorption

Perguntas frequentes

Research shows that regular vitamin C supplementation does not prevent colds in the general population, but it may modestly reduce cold duration by about 8% in adults (roughly half a day shorter). However, in people under extreme physical stress (marathon runners, soldiers), regular vitamin C supplementation can reduce cold incidence by up to 50%. Taking vitamin C after cold symptoms begin has little to no effect on duration or severity. A balanced diet with adequate vitamin C is the best approach for immune support.

Smoking generates enormous amounts of free radicals and oxidative stress, which rapidly deplete vitamin C stores. Smokers have 25–40% lower plasma vitamin C levels than non-smokers, even with similar dietary intake. The increased oxidative burden means smokers metabolize vitamin C faster and require approximately 35 mg more per day than non-smokers. Secondhand smoke exposure also increases vitamin C requirements, though to a lesser degree.

Yes, high-dose vitamin C (typically above 1,000–2,000 mg/day) can increase urinary oxalate excretion, which may raise the risk of calcium oxalate kidney stones in susceptible individuals—particularly those with a history of stones or kidney disease. The body converts some excess vitamin C to oxalate, which can crystallize in the urinary tract. People at risk of kidney stones should limit vitamin C supplements to standard recommended amounts and stay well hydrated.

Biomarcadores relacionados

FeFerro sérico FerritinFerritina Vit AVitamin A Vit KVitamin K

Leitura relacionada

Condições

Anemia →Asma →

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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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.