Vitamin C, also known as ascorbic acid, is a crucial nutrient for human health, renowned for its role as a powerful antioxidant. It's essential for the synthesis of collagen, a protein vital for the maintenance of skin, blood vessels, bones, and cartilage. Vitamin C also enhances the absorption of iron from plant-based foods, bolsters the immune system, and aids in wound healing. As a water-soluble vitamin, it needs to be regularly supplied in the diet since the body cannot store it. Optimal levels of Vitamin C are necessary for these physiological functions and can be maintained through consumption of fruits like oranges, strawberries, kiwi, and vegetables like broccoli, bell peppers, and spinach.
Nutrients that affect Vitamin C include iron, which is better absorbed with Vitamin C, and protein; excessive protein might hinder its absorption. Zinc, in high doses, can interfere with Vitamin C absorption and vice versa. Vitamin C may impact copper metabolism, and it works synergistically with other antioxidants like Vitamin E, helping regenerate oxidized Vitamin E. The interactions with B vitamins and a slight increase in excretion due to caffeine are also important considerations.
Deficiency of Vitamin C leads to scurvy, a condition rarely seen in modern times but can occur with extremely poor dietary habits. Early symptoms of deficiency include weakness, fatigue, and sore gums. As it progresses, scurvy can cause joint pain, poor wound healing, tooth loss, and anemia. Severe Vitamin C deficiency compromises the integrity of blood vessels, leading to bleeding gums and bruising. Children and the elderly, individuals with certain chronic illnesses, smokers, and those with limited dietary variety are at higher risk of deficiency.
Vitamin C toxicity is rare, as excess amounts are excreted in the urine. However, extremely high doses (usually from supplements) can lead to side effects like diarrhea, nausea, and abdominal cramps. There's also a potential risk of excess iron absorption in individuals with conditions like hemochromatosis. For most people, a diet rich in various fruits and vegetables provides adequate Vitamin C, ensuring its antioxidant and immune-boosting benefits without the risk of deficiency or toxicity. Supplementation should be approached cautiously and is generally only necessary for those with identified deficiencies or increased requirements.
To maintain healthy Vitamin C levels:
Consume a variety of vitamin C-rich foods daily, including citrus fruits, berries, kiwi, bell peppers, broccoli, and leafy greens.
Minimize cooking times and temperatures when preparing vitamin C-rich foods, as heat can degrade the vitamin. Opt for steaming or quick stir-frying instead of boiling.
Pair vitamin C-rich foods with iron sources, especially plant-based iron, to enhance absorption.
Avoid smoke (even secondhand smoke), as it depletes vitamin C.
Be mindful of excessive caffeine intake, which can slightly increase vitamin C excretion.
Vitamin C can be measured in: mg/100mL, mg/dL, mg/L, mg%, µg/mL, µmol/L
Reference ranges represent typical values for healthy individuals. Your healthcare provider must interpret your specific results.
| Age Range | Gender | Unit | Optimal | Normal | Source |
|---|---|---|---|---|---|
| All ages | All genders | mg/dL | - | 0.4 - 1.5 | Burnham, 2023 |
As an antioxidant, vitamin C can reduce oxidative stress and inflammation. It supports various cellular functions of both the innate and adaptive immune system. High vitamin C levels are associated with reduced levels of CRP and other inflammatory markers.[Crook, 2022][Jafarnejad, 2018][Carr, 2017]
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Vitamin C significantly enhances iron absorption from plant-based sources, potentially helping optimize ferritin levels in those with deficiency. Studies demonstrate that combining vitamin C with iron-rich meals can increase absorption by up to 300%. This relationship makes vitamin C status crucial for those trying to build iron stores through dietary approaches.[Saunders, 2013]
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Vitamin C is one of the factors enhancing absorption of selenium[Groff, 1995].
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Vitamin C (ascorbic acid) is a water-soluble antioxidant that humans cannot synthesise — unlike most mammals. The blood test measures plasma ascorbic acid concentration, which reflects recent dietary intake (it turns over within days). Because vitamin C is not stored in large amounts, plasma levels can drop rapidly with low dietary intake. A separate measure, leukocyte vitamin C, reflects tissue stores more accurately but is not routinely available from standard labs.
Vitamin C is essential for collagen synthesis (maintaining skin, tendons, blood vessels, bones, and cartilage), immune function, iron absorption (it converts dietary non-haem iron from Fe³⁺ to the more absorbable Fe²⁺), neurotransmitter production, and antioxidant protection. The body needs a continuous dietary supply — consuming vitamin C-rich foods daily is the most reliable way to maintain adequate plasma levels.
Reference ranges vary by laboratory. Some labs report in mg/L or µmol/L; use the blood test unit converter to convert between units. Men typically have slightly lower plasma vitamin C than women at equivalent intakes, partly due to body composition differences.
Vitamin C deficiency is rare in developed countries but still occurs — particularly in people with very restricted diets (alcohol dependence, food insecurity), malabsorption conditions, smokers (who have ~40% higher requirements), and in elderly people with limited dietary variety. The classical deficiency disease is scurvy.
Symptoms progress with severity of deficiency:
People with inflammatory bowel disease or Crohn's disease may have impaired vitamin C absorption. Low vitamin C is also associated with increased markers of inflammation — studies indicate that vitamin C supplementation reduces CRP in people with elevated inflammatory markers. See the Cardiovascular Health topic page. For comprehensive nutritional context, see the B vitamins blood test guide.
As a water-soluble vitamin, excess vitamin C is normally excreted in urine. Very high plasma levels from supplementation can occasionally cause gastrointestinal symptoms (diarrhoea, nausea) at doses above 2,000 mg/day. More clinically significant: very high doses can increase urinary oxalate excretion, potentially raising kidney stone risk in susceptible individuals. The EU and US Tolerable Upper Intake Level is 2,000 mg/day for adults. High vitamin C can also interfere with blood glucose test strips (some point-of-care devices) — relevant for people with diabetes.
Most laboratories consider plasma vitamin C of 0.4–1.5 mg/dL (23–85 µmol/L) as the normal range. Tissue saturation is generally achieved above 0.6 mg/dL. Levels below 0.2 mg/dL indicate deficiency; below 0.1 mg/dL carries risk of scurvy.
Research suggests vitamin C does not prevent colds in the general population when taken as a supplement, but may reduce duration by roughly half a day (about 8%) in adults. For people under heavy physical stress (e.g., marathon runners, soldiers in extreme conditions), supplementation may reduce cold incidence. The evidence does not support high-dose megadosing for prevention in typical populations.
The IOM Recommended Dietary Allowance (RDA) is 75 mg/day for adult women and 90 mg/day for adult men. Smokers need an additional 35 mg/day. The Tolerable Upper Intake Level is 2,000 mg/day. A single medium orange provides about 70 mg; a cup of red bell pepper provides about 190 mg.
Yes — consuming vitamin C alongside iron-rich plant foods or iron supplements significantly enhances non-haem iron absorption (by up to 4-fold). This is particularly beneficial for vegetarians, vegans, pregnant women, and people with iron deficiency anaemia. Drinking a glass of orange juice with iron supplements or eating citrus alongside lentils, beans, or spinach are practical strategies.
Yes. Vitamin C is water-soluble and heat-sensitive; boiling vegetables can destroy 40–60% of their vitamin C content. Steaming, stir-frying, or eating raw where possible preserves more. Storing cut fruit and vegetables for extended periods also reduces vitamin C content.
At-risk groups include smokers (higher oxidative stress), people with alcohol dependence, those with very limited dietary variety (particularly if avoiding fruits and vegetables), people with malabsorption conditions (Crohn's, ulcerative colitis, bariatric surgery), and the elderly with poor diets or social isolation.
This page is for educational purposes only. Vitamin C reference ranges vary between laboratories and assay methods. A result outside published ranges does not necessarily indicate disease. Always discuss your results with a qualified healthcare provider. Health3 is a tracking and awareness tool, not a diagnostic service.
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