Vitamin C, total ascorbic acid

Vitamin C, or ascorbic acid, is a water-soluble vitamin the body cannot make or store, so it has to come from food every day. It builds collagen for skin, blood vessels, and bone; helps the body absorb iron from plants; and acts as an antioxidant that neutralizes free radicals. Citrus fruit, peppers, and berries are the richest sources.

What is vitamin C

Ascorbic acid is a small, water-soluble molecule that the body uses as a cofactor for enzymes that build collagen — the structural protein in skin, blood vessels, tendons, and bone — and for enzymes involved in making carnitine and certain neurotransmitters. Because it dissolves in water rather than fat, the body does not store meaningful reserves of it, and any intake above what tissues need is filtered out through the kidneys. Humans, unlike most other mammals, lost the ability to synthesize vitamin C from glucose over the course of evolution, which is why it has to be obtained from the diet. In FoodData Explorer's own data, the most concentrated sources by measured amount are fortified low-calorie drink powders, dried coriander leaf and parsley, guavas, and raw peppers; among whole foods people actually eat in quantity, guavas, red bell peppers, Brussels sprouts, citrus fruit such as navel oranges, and cruciferous vegetables like broccoli and cauliflower rank consistently high.

Health benefits of vitamin C

• Collagen synthesis and wound healing. Vitamin C is a required cofactor for the enzymes that stabilize collagen's triple-helix structure, which is why MedlinePlus lists impaired wound healing and skin changes among the effects of low intake — the flip side of an evidence-backed structural role, not a claim that extra vitamin C speeds up healing in people who are already getting enough.
• Non-heme iron absorption. Harvard T.H. Chan School of Public Health, The Nutrition Source notes that vitamin C substantially improves absorption of non-heme iron from plant foods when eaten in the same meal, which is one reason vitamin C–rich produce is often recommended alongside iron-rich, plant-based meals.
• Common cold — modest effect at best. The same Harvard review reports that vitamin C supplementation has not been shown to reduce how often people catch colds, though some trials found a modest reduction in cold duration; it is not a treatment that prevents illness.
• Gout risk. Harvard's Nutrition Source cites the Physicians' Health Study II, in which men taking 500 mg of vitamin C daily had a modestly lower rate of newly diagnosed gout — an association from a supplement trial, not evidence that dietary intake alone produces the same effect.
• Cardiovascular disease and cancer — inconclusive. Harvard's review is explicit that randomized controlled trials have not found that vitamin C supplements reduce cardiovascular disease or cancer risk, despite earlier observational studies suggesting a link — a case where the evidence base doesn't support a benefit claim.

How much you need

The National Institutes of Health Office of Dietary Supplements sets the Recommended Dietary Allowance (RDA) for vitamin C at 90 mg/day for adult men and 75 mg/day for adult women, rising to 85 mg/day during pregnancy and 120 mg/day (115 mg/day for lactating teens) during lactation. People who smoke are advised to add 35 mg/day to their target because smoking increases vitamin C turnover. The Tolerable Upper Intake Level (UL) for adults is 2,000 mg/day from food and supplements combined; above that, gastrointestinal upset becomes more likely. These figures are not yet populated in this project's own nutrient_rda table, so they are cited directly to NIH ODS here — the NIH Office of Dietary Supplements, Vitamin C Health Professional Fact Sheet — rather than pulled from a live DB value. (Note: this specific ODS fact sheet blocks automated fetching; its figures were corroborated through Harvard's Nutrition Source, which independently states the same 90 mg/75 mg RDA, 35 mg smoker addition, and 2,000 mg UL.)

Signs of deficiency and excess

A sustained shortfall shows up first as fatigue, easy bruising, and inflamed or bleeding gums; MedlinePlus describes poor wound healing, hair and skin changes, nosebleeds, and joint pain as further signs, with frank scurvy — a severe deficiency that also weakens tooth enamel and skin integrity — occurring mainly in older, malnourished adults today rather than the general population. On the excess side, vitamin C from food alone essentially never reaches problematic levels; concerns arise only with high-dose supplementation. Harvard's Nutrition Source notes that intake well above the UL is associated with gastrointestinal distress, an increased risk of kidney stones, and elevated uric acid.

Warnings & interactions

High-dose vitamin C supplementation (generally above 1,000 mg/day) has been reported to reduce the anticoagulant effect of warfarin, and there is concern that high-dose antioxidant supplementation during chemotherapy could interfere with treatments that work in part through oxidative mechanisms — a reason to discuss any supplement, not dietary intake, with an oncology team before use. Because vitamin C meaningfully increases dietary iron absorption, people with hemochromatosis or other iron-overload conditions are generally advised to be cautious with vitamin C supplements specifically, since added iron absorption could worsen iron accumulation. People with a history of kidney stones or chronic kidney disease are also advised against high-dose supplementation given the oxalate-conversion pathway noted above. These interaction and caution points are well documented for supplemental, high-dose vitamin C; none of them apply to the amounts found naturally in food.

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