Vitamin C (ascorbic acid)

vitaminL-ascorbic acid

What is it

Ascorbic acid is the chemical name for vitamin C, the water-soluble vitamin essential for collagen synthesis, antioxidant defense, and immune function. It is the most common form found in supplements.

How it works

Ascorbic acid acts as a cofactor for enzymes that build collagen, the protein that gives structure to skin, blood vessels, tendons, and bones. It also recycles other antioxidants like vitamin E, supports neurotransmitter synthesis, and substantially increases absorption of non-heme iron from plant foods. It is absorbed in the small intestine through both passive diffusion and active transport. At low to moderate doses absorption is highly efficient, but at very high oral doses (above 1,000 mg) the fraction absorbed drops sharply and excess is excreted in urine.

Evidence for 5 uses

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

Scurvy prevention and treatment

Grade A

Strong evidence

Ascorbic acid prevents and cures scurvy, the classic vitamin C deficiency disease characterized by impaired collagen synthesis. This is one of the most definitively established vitamin effects in medicine.

Enhancing iron absorption

Grade A

Strong evidence

Taking ascorbic acid with non-heme iron substantially increases iron absorption. Commonly recommended alongside iron supplements for treating iron deficiency.

Common cold duration

Grade B

Good evidence

Daily supplementation shortens cold duration by roughly 8 to 14 percent. It does not prevent colds in the general population.

Cardiovascular disease prevention

Grade C

Moderate evidence

Observational studies link higher vitamin C intake to lower cardiovascular risk, but supplement trials have not consistently shown benefit.

Cancer prevention

Grade D

Mixed evidence

Dietary vitamin C correlates with lower cancer risk in observational studies, but ascorbic acid supplements have not shown clear cancer prevention in randomized trials.

Dosage

The RDA is 90 mg per day for adult men and 75 mg for women, with an additional 35 mg for smokers. Most ascorbic acid supplements contain 500 to 1,000 mg. The tolerable upper limit for adults is 2,000 mg per day, set primarily to avoid gastrointestinal side effects.

When and how to take it

Ascorbic acid does not require food for absorption, but taking it with meals can reduce stomach upset in sensitive people. Because the body excretes excess in urine within hours, splitting doses above 500 mg into two or three smaller doses across the day maintains higher blood levels. If you take iron supplements, taking ascorbic acid with them substantially boosts iron absorption — a useful pairing for 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%
Broccoli, 1/2 cup cooked	51 mg	57%
Strawberries, 1/2 cup	49 mg	54%
Grapefruit, 1/2 medium	39 mg	43%
Cantaloupe, 1/2 cup	29 mg	32%

Safety

Ascorbic acid is generally well tolerated. Doses above 1,000 to 2,000 mg per day commonly cause diarrhea, bloating, and stomach cramps. Very high chronic doses may modestly increase kidney stone risk in people with a history of oxalate stones. The acidic nature can erode tooth enamel if chewed or held in the mouth — swallow tablets whole and rinse the mouth after chewable forms.

Who should be cautious

People with hemochromatosis or other iron-overload conditions should avoid high-dose ascorbic acid. People with kidney disease or a history of kidney stones should keep intake near the RDA. Pregnant women need slightly more (85 mg/day) and breastfeeding women need 120 mg/day, but standard doses are safe.

Interactions

Ascorbic acid increases non-heme iron absorption — helpful for iron deficiency but a concern in hemochromatosis. High doses may reduce effectiveness of some chemotherapy drugs (consult your oncologist) and have been suggested to interact with warfarin, though evidence is mixed. Estrogen-containing medications can lower vitamin C levels modestly.

Frequently asked questions

Is ascorbic acid the same as vitamin C?⌄

Yes. Ascorbic acid is the chemical name for vitamin C and is the form your body uses. Other forms in supplements (sodium ascorbate, Ester-C) are also vitamin C, just buffered.

Does ascorbic acid hurt the stomach?⌄

Some people experience stomach upset at higher doses because of its acidity. Taking it with food or using buffered forms helps.

How much ascorbic acid can I take per day?⌄

The upper limit is 2,000 mg per day for adults. Beyond that you risk gastrointestinal side effects with no added benefit.

Does ascorbic acid help iron absorption?⌄

Yes, substantially. Taken at the same time as iron from plants or supplements, ascorbic acid can multiply absorption.

Can I get enough ascorbic acid from food?⌄

Yes. One serving of citrus fruit, bell pepper, broccoli, or strawberries provides the daily requirement for most adults.

References

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

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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.