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.

Vitamins & Minerals

What is 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.

Why It Matters

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.

Normal Reference Ranges

Group	Range	Unit
Adults	0.4–1.5	mg/dL
Deficient	<0.2	mg/dL
Scurvy risk	<0.1	mg/dL

Reference ranges may vary by laboratory. Always compare results to the ranges provided by your testing facility.

What High Ascorbate Levels Mean

Common Causes

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

Possible Symptoms

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

What to do: 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.

What Low Ascorbate Levels Mean

Common Causes

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

Possible Symptoms

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

What to do: 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.

When Is Ascorbate Testing Recommended?

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

Frequently Asked Questions

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.

Related Biomarkers

FeSerum Iron FerritinFerritin Vit AVitamin A Vit KVitamin K

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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Reference ranges may vary between laboratories. Always consult your healthcare provider for interpretation of your specific test results.