Vitamin C

vitamin

Best with a mealTake with food

What is it

Vitamin C is a water-soluble vitamin and powerful antioxidant essential for collagen synthesis, immune function, and iron absorption. Humans cannot make it and must obtain it from food or supplements.

How it works

Vitamin C acts as a cofactor for enzymes that build collagen, the structural protein in skin, blood vessels, tendons, and bones. Without it, collagen synthesis breaks down — the underlying problem in scurvy. It also regenerates other antioxidants like vitamin E, supports neurotransmitter synthesis, and helps the body absorb non-heme iron from plant foods. In immune cells, vitamin C accumulates at concentrations much higher than in plasma, where it supports the production and function of white blood cells. It is rapidly absorbed in the small intestine but at high doses absorption efficiency drops sharply, with excess excreted in urine.

Evidence for 6 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Scurvy prevention

Grade A

Strong evidence

Vitamin C completely prevents and cures scurvy. This is the original and most definitive evidence for vitamin C, established centuries ago.

Iron absorption enhancement

Grade A

Strong evidence

Vitamin C taken with non-heme iron (from plants or supplements) substantially increases iron absorption by keeping iron in its more absorbable ferrous form. Recommended alongside iron supplements for deficiency.

Common cold severity and duration

Grade B

Good evidence

Regular daily supplementation does not prevent colds in the general population, but it shortens duration by about 8 percent in adults and 14 percent in children. Larger benefits are seen in people under physical stress like marathon runners.

Wound healing

Grade B

Good evidence

Adequate vitamin C supports collagen formation needed for healing. Deficiency clearly impairs wound healing; supplementation above the RDA in non-deficient people has uncertain additional benefit.

Cardiovascular disease prevention

Grade C

Moderate evidence

Observational data suggest higher vitamin C intake correlates with lower cardiovascular risk, but randomized trials of supplements have not consistently shown benefit.

Cancer prevention

Grade D

Mixed evidence

Dietary vitamin C from fruits and vegetables is associated with lower cancer risk in observational studies, but supplement trials have been largely negative.

3 commercial forms

Ascorbic acid

standard, well absorbed, acidic

The most common and least expensive form. Highly bioavailable, but can cause stomach upset in sensitive people.

Sodium ascorbate / mineral ascorbates (Ester-C)

buffered, gentler on stomach

Mineral-buffered forms are less acidic and easier on the stomach. Bioavailability is similar to plain ascorbic acid.

Liposomal vitamin C

claims higher absorption

Marketed as delivering more vitamin C into cells. Some pharmacokinetic studies show higher blood levels, but clinical benefit over standard forms is unproven.

Dosage

The RDA is 90 mg per day for adult men and 75 mg for adult women, with an additional 35 mg for smokers. Most multivitamins provide 60 to 100 mg, while standalone supplements often contain 500 to 1,000 mg. The tolerable upper intake level for adults is 2,000 mg per day, mainly to avoid gastrointestinal side effects.

When and how to take it

Vitamin C is water-soluble and does not require food for absorption, though some people find it gentler on the stomach when taken with a meal. Because the body excretes excess vitamin C in urine within hours, splitting larger daily doses (such as 1,000 mg) into smaller doses taken throughout the day improves blood levels. If you take iron supplements, vitamin C taken at the same time can boost iron absorption substantially — useful for people with iron deficiency.

Food sources

Food	Amount	%DV
Red bell pepper, 1/2 cup raw	95 mg	106%
Orange, 1 medium	70 mg	78%
Kiwi, 1 medium	64 mg	71%
Strawberries, 1/2 cup	49 mg	54%
Broccoli, 1/2 cup cooked	51 mg	57%
Brussels sprouts, 1/2 cup cooked	48 mg	53%
Grapefruit, 1/2 medium	39 mg	43%
Tomato juice, 3/4 cup	33 mg	37%
Potato (baked, with skin)	17 mg	19%

Safety

Vitamin C is generally very safe. Doses above 1,000 to 2,000 mg per day can cause diarrhea, nausea, and stomach cramps because unabsorbed vitamin C draws water into the gut. Very high doses may increase the risk of kidney stones in susceptible people, particularly those with a history of oxalate stones. Megadoses (10,000+ mg) provide no additional benefit because saturation of intestinal absorption and renal excretion means excess is simply lost in urine.

Who should be cautious

People with kidney disease or a history of kidney stones should keep intake near the RDA. People with hemochromatosis or other iron-overload conditions should avoid high-dose vitamin C because it increases iron absorption. Pregnant and breastfeeding women have slightly higher needs (85 mg and 120 mg respectively) but standard doses are safe.

Interactions

Vitamin C enhances absorption of non-heme iron, which is usually beneficial but can be a problem for people with hemochromatosis. High doses may reduce the effectiveness of some chemotherapy drugs and have been suggested to interact with anticoagulants like warfarin, though evidence is limited. Estrogen and oral contraceptives can raise vitamin C requirements modestly.

Frequently asked questions

Does vitamin C prevent colds?⌄

No, regular supplementation does not prevent colds in the general population. It does modestly shorten duration and may reduce severity, particularly in people under physical stress.

How much vitamin C is too much?⌄

Doses above 2,000 mg per day commonly cause diarrhea and stomach upset. There is no benefit to megadosing because excess is excreted in urine.

Can I take vitamin C on an empty stomach?⌄

Yes, but it may cause mild stomach upset in sensitive people. Buffered forms (sodium ascorbate, Ester-C) are gentler.

Is liposomal vitamin C worth the extra cost?⌄

Probably not for most people. Pharmacokinetic data show higher blood levels, but clinical outcome data showing it works better than standard forms is lacking.

Does smoking affect vitamin C needs?⌄

Yes. Smokers need an additional 35 mg per day above the standard RDA because smoking increases oxidative stress and vitamin C turnover.

References

NIH ODS Vitamin C Fact Sheet — NIH Office of Dietary Supplements link

Track Vitamin C with Pilora

Set up dose reminders, check interactions, and join the community in the Pilora iPhone app.

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Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.