Vitamin C

Medically reviewed by Prof. Giorgi Pkhakadze, MD, MPH, PhD — GMJ Editorial Board

What is Vitamin C?

Vitamin C, also known by its scientific name ascorbic acid, is an essential water-soluble vitamin that the human body cannot produce on its own. As a member of the vitamin category, it must be obtained through diet or supplementation. Unlike fat-soluble vitamins, vitamin C is not stored in the body for extended periods and excess amounts are excreted through urine, making regular intake necessary.

The Recommended Dietary Allowance (RDA) for vitamin C is 90 mg per day for adult men and 75 mg per day for adult women, with higher amounts needed during pregnancy (85 mg) and breastfeeding (120 mg). The Tolerable Upper Intake Level (UL) is set at 2,000 mg per day for adults.

Health benefits & uses

Strong evidence: Vitamin C is essential for collagen synthesis, wound healing, and immune system function. It serves as a powerful antioxidant, protecting cells from oxidative stress and supporting the absorption of non-heme iron from plant-based foods. Clinical evidence strongly supports its role in preventing and treating scurvy, a deficiency disease.

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Moderate evidence: Research suggests vitamin C may help reduce the duration and severity of common cold symptoms, particularly in people exposed to extreme physical stress or cold environments. Studies also indicate potential benefits for cardiovascular health through its antioxidant properties and role in maintaining healthy blood vessels.

Limited evidence: Some studies suggest vitamin C supplementation may support skin health, reduce the risk of certain chronic diseases, and potentially enhance exercise performance. However, more research is needed to establish definitive therapeutic benefits in these areas.

How it works

Vitamin C functions as a cofactor in numerous enzymatic reactions throughout the body. It plays a crucial role in collagen synthesis by helping convert proline and lysine into hydroxyproline and hydroxylysine, essential components of stable collagen structure. As an antioxidant, vitamin C donates electrons to neutralize free radicals, protecting cellular components from oxidative damage.

The vitamin enhances immune function by supporting the production and function of white blood cells, particularly neutrophils, lymphocytes, and phagocytes. It also helps maintain the integrity of epithelial barriers and supports the skin’s defense system against pathogens.

Dosage

For general health maintenance, the RDA provides adequate vitamin C for most healthy adults: 75-90 mg daily. However, certain circumstances may warrant higher doses under healthcare provider guidance.

Typical supplemental doses range from 100-1,000 mg daily. For immune support during illness, some practitioners recommend 1,000-3,000 mg daily in divided doses. Smokers require an additional 35 mg daily above the standard RDA due to increased oxidative stress.

Always consult with a healthcare provider before exceeding the UL of 2,000 mg daily, especially if you have underlying health conditions or take medications.

Food sources

Excellent food sources of vitamin C include citrus fruits (oranges, grapefruits, lemons), berries (strawberries, blueberries, cranberries), kiwi fruit, and tropical fruits like papaya and mango. Vegetables rich in vitamin C include bell peppers, broccoli, Brussels sprouts, cauliflower, cabbage, and leafy greens.

Other notable sources include tomatoes, potatoes, cantaloupe, and fortified foods. Cooking can reduce vitamin C content, so consuming fresh or lightly cooked fruits and vegetables maximizes intake.

Safety & side effects

Vitamin C is generally safe for most people when taken within recommended doses. Being water-soluble, excess amounts are typically excreted through urine. However, high doses (above 1,000-2,000 mg daily) may cause gastrointestinal side effects including nausea, diarrhea, stomach cramps, and heartburn.

Very high doses may increase the risk of kidney stones in susceptible individuals and can interfere with certain medical tests, including glucose monitoring in diabetics.

Interactions

Vitamin C can enhance the absorption of iron supplements and iron from plant-based foods, which may be beneficial for those with iron deficiency but potentially problematic for individuals with iron overload conditions.

High doses may reduce the effectiveness of certain chemotherapy drugs and blood-thinning medications like warfarin. Vitamin C can also interact with aluminum-containing antacids, potentially increasing aluminum absorption.

Some studies suggest that vitamin C may interfere with vitamin B12 absorption when taken together in large doses.

Who should be cautious

Individuals with kidney disease, kidney stones, or a history of oxalate stones should exercise caution with high-dose vitamin C supplementation. People with glucose-6-phosphate dehydrogenase (G6PD) deficiency may experience hemolytic anemia with very high doses.

Those with hemochromatosis or other iron overload conditions should be cautious due to vitamin C’s iron-enhancing effects. Pregnant and breastfeeding women should not exceed recommended doses without medical supervision.

Frequently asked questions

Can I take too much vitamin C?

While vitamin C toxicity is rare due to its water-soluble nature, doses above 2,000 mg daily can cause digestive upset and other side effects. The body can only absorb limited amounts at once, making megadoses largely unnecessary.

Is natural vitamin C better than synthetic?

Scientific evidence shows that synthetic ascorbic acid is chemically identical to naturally occurring vitamin C and equally bioavailable. Natural sources may provide additional beneficial compounds like flavonoids, but both forms effectively meet vitamin C needs.

Should I take vitamin C when I feel a cold coming on?

While vitamin C may not prevent colds in the general population, regular supplementation might reduce cold duration and severity. Starting supplementation when symptoms begin shows limited benefit compared to consistent daily intake.

Can vitamin C help with iron absorption?

Yes, vitamin C significantly enhances the absorption of non-heme iron from plant sources when consumed together. This makes it particularly beneficial for vegetarians and those with iron deficiency.

How long does vitamin C stay in the body?

Vitamin C has a relatively short half-life in the body, with most being metabolized or excreted within 24-48 hours. This is why daily intake is recommended for maintaining adequate levels.