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Vitamin C
An essential vitamin in fruit and vegetables such as citrus and peppers. It is widely sold for colds and promoted for many other conditions.
Explained simply · Last reviewed
What it is
Vitamin C, also known as L-ascorbic acid, is a water-soluble vitamin. The Office of Dietary Supplements (ODS), part of the US National Institutes of Health, describes it as naturally present in some foods, added to others, and sold as a dietary supplement. It says that humans, unlike most animals, cannot make vitamin C, so it has to come from the diet.
More about Vitamin C
The Office of Dietary Supplements (ODS), part of the US National Institutes of Health, describes it as naturally present in some foods, added to others, and sold as a dietary supplement. It says that humans, unlike most animals, cannot make vitamin C, so it has to come from the diet.
ODS says the body needs vitamin C to make collagen, a building block of connective tissue that matters for wound healing, as well as L-carnitine and some brain chemicals. ODS adds that it is an antioxidant, plays a part in immune function, and helps the body absorb the form of iron found in plant foods. It names citrus fruits, red and green peppers, kiwifruit, broccoli, strawberries and Brussels sprouts among the best sources, and notes that cooking can reduce how much of it food contains.
Vitamin C has a long history. ODS recounts that in the mid-1700s a British Navy surgeon, James Lind, found that citrus fruits or juices could cure scurvy among sailors, though ascorbic acid was not proven to be the active component until 1932. A 2013 Cochrane review describes how interest in vitamin C for colds took off in the 1970s, when Nobel laureate Linus Pauling concluded that it would prevent and alleviate them. The reviewers say it has been widely sold and used for colds. ODS reports that in 1999–2000 about 12% of US adults took a separate vitamin C supplement, and that it has been promoted for many other conditions.
Also known as: ascorbic acid, L-ascorbic acid, ascorbate, sodium ascorbate, calcium ascorbate
At a glance
Safety: known risks, 6 groups who should avoid it or take extra care and 2 documented interactions. See Safety ↓Claims made about Vitamin C, and how strong the evidence is for each:
- Prevents scurvy, the disease caused by vitamin C deficiencyEvidence rating: Strong
- Taken every day, lowers the chance of catching a cold in the general populationEvidence rating: Evidence against
- Taken every day, makes colds shorter and milderEvidence rating: Moderate
- Taken once a cold starts, makes it shorter or milderEvidence rating: Insufficient
- Lowers the risk of heart attack, stroke and other cardiovascular diseaseEvidence rating: Evidence against
- Lowers the risk of developing cancerEvidence rating: Evidence against
- Lowers blood pressureEvidence rating: Limited
Longevity and aging claims
Claims made about Vitamin C and aging, and how strong the evidence is for each. A change in a marker is not the same as a longer life.
Each rating follows our published rules and the sources cited for it. We don’t add our own medical judgment. How we rate
Safety
Read this before the ratings below.
Risks
- ODS, part of the US National Institutes of Health, says vitamin C has low toxicity and is not believed to cause serious adverse effects at high intakes. The most common complaints are diarrhea, nausea, abdominal cramps and other stomach and bowel upsets, caused by the osmotic effect of unabsorbed vitamin C in the gut.
- Kidney stones: ODS says high intakes could raise the oxalate and uric acid passed in urine, which could contribute to kidney stones, especially in people with kidney disorders. It says studies conflict, so it is not clear whether vitamin C plays a role. The best evidence that it contributes is in people with pre-existing hyperoxaluria.
- Iron overload: vitamin C helps the body absorb iron from plant foods. ODS says this does not appear to be a concern in healthy people, but that in hereditary hemochromatosis, chronic high doses could worsen iron overload and damage tissue.
- In one US study of postmenopausal women with diabetes, taking supplemental vitamin C (at least 300 mg a day) was linked to a higher risk of dying from cardiovascular disease. ODS says the mechanism is unclear, the finding comes from a subgroup in an epidemiological study, no other epidemiological study has seen it, and its significance is uncertain.
- Kidney stones in men: a 2022 evidence review for the US Preventive Services Task Force reports two cohort studies, both in men, that suggest a link between vitamin C supplements and kidney stones. In one, Swedish men who reported taking vitamin C supplements had a higher risk of a first kidney stone over 11 years (risk ratio 1.92, 1.33 to 2.77). The review calls this weak evidence, rated low strength for increased risk on its own scale, and notes that both studies asked about supplement use only once, by questionnaire. In its two trials, it found no increase in serious or non-serious harms from long-term vitamin C use, and it rates the evidence on these other harms low strength for no increased risk, on its own scale.
- Cataracts: the same review reports that two Swedish cohort studies linked vitamin C supplements to more cataract surgery, while a US cohort study and the large US trial found no association. It describes the cohort results as conflicting, and rates the evidence low strength for no increased risk of cataract, on its own scale.
- In seven large cold trials reviewed by Cochrane in 2013, 5.8% of people taking vitamin C and 6.0% of people taking placebo reported symptoms they put down to their tablets. No serious symptoms were reported.
Who should avoid it or take extra care
- People with hereditary hemochromatosis: see the iron overload risk above.
- People with kidney disorders or hyperoxaluria: see the kidney stone risk above.
- People having chemotherapy or radiation therapy: ODS says to consult an oncologist before taking vitamin C or other antioxidant supplements, especially in high doses.
- Infants: ODS states that formula and food should be the only sources of vitamin C for infants.
- Children and teenagers: their upper limits are lower than for adults, according to ODS.
- Anyone taking the medications listed below on a regular basis: ODS advises discussing vitamin C intake with a health care provider.
Documented interactions
- Chemotherapy and radiation therapy: ODS calls the safety and efficacy of vitamin C and other antioxidants during cancer treatment controversial. Some data suggest antioxidants might protect tumor cells from radiation and some chemotherapy drugs; other data suggest they might protect normal tissue or make treatment more effective. ODS notes that at least some of these data have been criticized for poor study design. It says it is unclear whether vitamin C taken by mouth could change vitamin C levels enough to have these effects. Source [1]
- Statins combined with niacin (for example simvastatin/Zocor with niacin): ODS says vitamin C, together with other antioxidants, may blunt the rise in HDL cholesterol that combined niacin and simvastatin therapy produces. It says it is not known whether this happens with other cholesterol treatments, and that health care providers should monitor lipid levels in people taking both statins and antioxidant supplements. Source [1]
Safety sources: Source [1]Source [2]Source [3]
What the evidence says
Each claim is rated on its own evidence. Ratings follow the scale on our methodology page.
Prevents scurvy, the disease caused by vitamin C deficiency Evidence rating: Strong
People take it to make sure they get enough vitamin C and never develop scurvy.
ODS, part of the US National Institutes of Health, states that too little vitamin C causes scurvy, and that through a varied diet most people should get enough to prevent it.
This claim rests on the Office of Dietary Supplements (ODS) at the US National Institutes of Health. It states that vitamin C deficiency causes scurvy. Early signs include fatigue, malaise and inflamed gums. As it progresses, collagen production fails and connective tissue weakens, causing bleeding into the skin (petechiae, ecchymoses and purpura), joint pain and poor wound healing. Left untreated, ODS says, scurvy is fatal.
ODS describes scurvy as rare in developed countries. It says that through a varied diet most people should get at least enough vitamin C to prevent scurvy. It names groups more likely to fall short: people who smoke or breathe secondhand smoke, infants fed evaporated or boiled cow’s milk, people who eat a limited variety of food, and people with malabsorption or some chronic diseases.
Note what this claim covers: the disease that deficiency causes. ODS says the recommended intakes are much higher than the amount needed to protect against deficiency. This is not a claim that extra vitamin C helps someone who already gets enough.
Sources: Source [1]
Taken every day, lowers the chance of catching a cold in the general population Evidence rating: Evidence against
People take it every day through the winter hoping to avoid catching colds.
A 2013 Cochrane review of trials in 10,708 people from the general community found that daily vitamin C did not reduce the number who caught a cold.
A 2013 Cochrane review pooled placebo-controlled trials of vitamin C taken every day. In 24 trial comparisons with 10,708 people from the general community, the risk of catching at least one cold was almost the same with vitamin C as with placebo (risk ratio 0.97, 95% confidence interval 0.94 to 1.00). The reviewers call this strong evidence that daily vitamin C has no effect on the number of people who catch colds. Trials that gave higher daily amounts found essentially the same.
In the same review, the exception was people under heavy, short-term physical stress. In five trials with 598 marathon runners, skiers and soldiers on subarctic exercises, the risk of a cold was about half as high with vitamin C (risk ratio 0.48, 0.35 to 0.64). The reviewers say caution is needed in generalizing this. They note that some of these symptoms may have come from airway narrowing after heavy exercise rather than from a virus. Two trials of longer physical stress, over two to three months, found no effect on colds.
ODS, part of the US National Institutes of Health, takes the same view. It says regular vitamin C does not appear to reduce the risk of colds in the general population. It adds that regular intakes might help people exposed to extreme exercise or cold, and people with marginal vitamin C status, such as older adults and people who smoke.
This page rates the claim for the general population only, the group the reviewers' main result covers.
Sources: Source [1]Source [2]
Taken every day, makes colds shorter and milder Evidence rating: Moderate
People take it daily hoping that, when they do catch a cold, it will be shorter and milder.
A 2013 Cochrane review found colds were 8% shorter in adults and 14% shorter in children taking vitamin C daily, and the reviewers call the practical relevance unclear.
The 2013 Cochrane review pooled 31 trial comparisons, covering 9,745 colds, in which people took vitamin C every day. Colds that began during the trials were 8% shorter in adults (95% confidence interval 3% to 12%) and 14% shorter in children (7% to 21%). In children given higher daily amounts, colds were 18% shorter. Severity, measured as days confined to home or off work or school, or on symptom scales, was also lower.
The reviewers call the effect consistent but modest, and say its practical relevance is not clear. In their opinion, this level of benefit does not justify long-term supplementation in its own right. Most trials were randomized and double-blind, and leaving out the others did not change the results. The review does not use GRADE ratings.
A 2023 meta-analysis by the same two authors looked at severity in trials of daily vitamin C. Across 15 comparisons from 10 trials, colds were 15% less severe (9% to 21%). It then took five trials that had found a significant effect on severe measures, such as days indoors or off school. In them, it found a 26% cut in those measures and no evidence of an effect on overall cold length, which it uses as a stand-in for mild symptoms. The authors say the P value for that difference should be read with some caution, and that the 2013 duration estimate should not be compared directly with this analysis. The analysis was not registered in advance.
ODS, part of the US National Institutes of Health, says regular vitamin C might shorten colds and ease symptoms in the general population.
Sources: Source [1]Source [2]Source [3]
Taken once a cold starts, makes it shorter or milder Evidence rating: Insufficient
People reach for it at the first sniffle hoping to shake the cold off faster.
A 2013 Cochrane review found no consistent effect when vitamin C was started after symptoms began, and says too few trials have been done, none in children.
The 2013 Cochrane review pooled seven comparisons, covering 3,249 colds, in which adults started vitamin C after cold symptoms began. It found no consistent effect on how long colds lasted or how severe they were. One large trial found a modest benefit, but the other trials did not. The reviewers conclude that, so far, taking vitamin C once a cold starts has not been shown to be effective.
The reviewers also stress how few of these trials exist, and that none studied children. One large adult trial reported benefit from a single very high dose on the first day, and two trials of five-day courses reported benefit. The reviewers point to the consistent effect seen with daily use and to what they describe as vitamin C’s low cost and safety, and suggest it may be worthwhile for people with colds to test individually whether it helps them. They call for more trials.
A 2023 meta-analysis by the same authors adds that the few therapeutic trials have methodological limitations, such as starting treatment too late and not continuing it long enough, and calls for more research.
ODS, part of the US National Institutes of Health, states that taking vitamin C after cold symptoms start does not appear to affect how long colds last or how severe the symptoms are. The source it cites for this is the 2007 version of the same Cochrane review, which the 2013 version replaced. This page follows the current review: too little evidence to show whether it helps, rather than evidence that it does not.
Sources: Source [1]Source [2]Source [3]
Lowers the risk of heart attack, stroke and other cardiovascular disease Evidence rating: Evidence against
People take it hoping to protect their heart and blood vessels.
A 2017 Cochrane review found no difference in major cardiovascular events in one large trial of US male doctors, at low certainty; ODS says trials give no convincing evidence of protection.
A 2017 Cochrane review looked for trials of vitamin C taken on its own for at least three months, by healthy adults or adults at raised risk of cardiovascular disease. It found eight trials with 15,445 people. Only one, the Physicians' Health Study II, reported heart attacks, strokes and deaths. It followed 14,641 middle-aged and older US male doctors for eight years.
In that trial, major cardiovascular events were no different with vitamin C than with placebo (hazard ratio 0.99, 95% confidence interval 0.89 to 1.10). The review reports similar results for heart attacks, strokes, angina and heart procedures. How sure the reviewers are (certainty) is low for these outcomes, because the evidence comes from one trial in one group of men. They rate death from cardiovascular disease very low.
The reviewers conclude there is currently no evidence that vitamin C supplements reduce the risk of cardiovascular disease, and that the evidence is limited to that one trial. They write that it was large and adequately powered, and clearly showed no effect on major cardiovascular events. Of the eight trials, four did not state their funding, and two declared both commercial and non-commercial funding.
ODS, part of the US National Institutes of Health, takes a similar view. It says most intervention trials do not give convincing evidence that vitamin C supplements protect against cardiovascular disease or reduce illness or death from it. It notes one trial in China in which vitamin C with molybdenum was followed by fewer deaths from stroke. It also cautions that trial participants may already have had vitamin C levels near saturation.
The US Preventive Services Task Force (USPSTF), in its 2022 recommendation, says two trials suggested vitamin C has no effect on death from any cause, cardiovascular events or cardiovascular deaths, though one was small and not powered for these outcomes. For single or paired nutrients other than beta carotene and vitamin E, it concludes that the current evidence is insufficient to assess the balance of benefits and harms for preventing cardiovascular disease or cancer. That is a weaker conclusion than this page's rating, which rests on the Cochrane review's finding of no effect.
Sources: Source [1]Source [2]Source [3]
Lowers the risk of developing cancer Evidence rating: Evidence against
People take it hoping its antioxidant action will help keep cancer away.
ODS states that results from most clinical trials suggest modest vitamin C supplementation, alone or with other nutrients, offers no benefit in preventing cancer.
This claim rests on ODS, part of the US National Institutes of Health. It says most case-control studies link high vitamin C intake from food to lower risk of several cancers. Cohort studies, it says, are inconsistent. It concludes that results from most clinical trials suggest modest vitamin C supplementation, alone or with other nutrients, offers no benefit in preventing cancer.
ODS describes a trial in US male doctors in which vitamin C and vitamin E did not reduce prostate or total cancer. In a trial in women with a history of cardiovascular disease, vitamin C had no significant effect on total cancer. In a French trial, a combined antioxidant supplement lowered cancer in men but not in women. ODS adds a caution: many trials did not measure vitamin C levels, and people already near saturation would be expected to see little difference.
A 2022 evidence review for the US Preventive Services Task Force found trial evidence on cancer in only one study, of 14,641 US male doctors. Over eight years, vitamin C was not associated with total cancer (hazard ratio 1.01, 95% confidence interval 0.92 to 1.10) or cancer deaths. The review rates the strength of this evidence low for no benefit, on its own scale, because it rests on one trial in men.
The Task Force itself (USPSTF), in its 2022 recommendation, says that one trial suggested vitamin C has no effect on cancer incidence or deaths. But for single or paired nutrients other than beta carotene and vitamin E, it concludes that the current evidence is insufficient to assess the balance of benefits and harms for preventing cardiovascular disease or cancer. That is a weaker conclusion than this page's rating. The page keeps evidence against because ODS and the Task Force's own vitamin C findings point to no benefit, and states the difference here.
This claim is about vitamin C taken by mouth to prevent cancer. ODS notes that vitamin C given into a vein can reach far higher blood levels than vitamin C by mouth. That is a different use and is not rated here.
Sources: Source [1]Source [2]Source [3]
Lowers blood pressure Evidence rating: Limited
People take it hoping it will bring their blood pressure down.
A 2012 review of 29 small, short trials found slightly lower blood pressure with vitamin C, and its authors say longer, larger trials are needed before it can be recommended.
A 2012 meta-analysis pooled 29 randomized trials of vitamin C taken by mouth, with 1,407 participants. The trials were small, with 10 to 120 people each, and lasted 2 to 26 weeks. Systolic blood pressure, the top number, fell by 3.84 mmHg more than with control (95% confidence interval 2.38 to 5.29). Diastolic blood pressure, the bottom number, fell by 1.48 mmHg (0.10 to 2.86).
Thirteen of the trials combined vitamin C with other vitamins or minerals. In the trials that gave vitamin C on its own, systolic pressure fell by 2.59 mmHg (1.38 to 3.81). The change in diastolic pressure was not statistically significant, which is too little evidence to show an effect either way.
The authors found wide differences between trials. Trials taking more blood pressure readings found smaller effects, and four trials said they left out blood pressure results because they were not significant. When the authors added these and other incompletely reported trials with imputed values, the reductions were smaller but remained significant. The authors conclude that larger, better-designed trials are needed before vitamin C supplements can be recommended to prevent high blood pressure or to add to its treatment.
An editorial in the same journal rated the review reasonably high quality. It called the blood pressure effect minor, and said the findings clearly fail to support advocating vitamin C supplements to lower blood pressure.
Sources: Source [1]Source [2]
Longevity and aging
What the cited sources report about lifespan, death from any cause, and markers studied in connection with aging. A change in a marker is not the same as a longer life. Each outcome is rated on its own evidence, on the same scale as the claims above.
Lowers the risk of death from any cause in adults Evidence rating: Insufficient
People take it hoping it will help them live longer.
A 2012 Cochrane review of 29 low-bias trials found no significant effect of vitamin C, alone or with other antioxidants, on death from any cause, and could not rule out small benefit or large harm.
This entry is about death from any cause in adults; no study cited here measured lifespan. A 2012 Cochrane review pooled randomized trials of antioxidant supplements taken by mouth, in healthy people and in people with stable diseases. For vitamin C, given alone or with other antioxidants, it found no significant effect on death in 29 trials at low risk of bias (risk ratio 1.02, 95% confidence interval 0.98 to 1.07).
The reviewers write that small beneficial or large harmful effects cannot be excluded. Their trial sequential analysis, a check on whether enough data have built up, did not reach a firm answer either way. They state there is no evidence that vitamin C may increase longevity. They also note that most of their trials tested combinations of supplements.
Feedback published with the review, written about its 2008 version, disputes its methods. One comment argued that the vitamin C doses tested were too small and too infrequent to be effective; the authors replied that claims are not valid proof.
The 2017 Cochrane review of vitamin C and cardiovascular disease reported death from any cause in one trial of 14,641 US male doctors over eight years (hazard ratio 1.07, 0.97 to 1.18). It rated this very low certainty, partly because eight years may be too short to detect an effect on deaths. This page reads both results as too little evidence to show whether vitamin C changes the risk of death either way.
Sources: Source [1]Source [2]
How and when to take it
What the cited sources say about taking it. Ask your doctor or pharmacist what applies to you.
The upper limit for adults is 2,000 mg a day
ODS gives a Tolerable Upper Intake Level of 2,000 mg for everyone aged 19 and over, including during pregnancy and lactation. It describes the upper limit as the maximum daily intake unlikely to cause adverse health effects, and says long-term intakes above it may increase the risk of adverse health effects. Source [1]
People who smoke need more vitamin C
ODS reports that people who smoke have lower vitamin C levels in their blood and white blood cells, and states that they require 35 mg more vitamin C per day than people who do not smoke. Source [1]
Talk to your oncologist first if you are having chemotherapy or radiation
ODS says individuals undergoing chemotherapy or radiation should consult their oncologist before taking vitamin C or other antioxidant supplements, especially in high doses. Source [1]
Which form the evidence used
Supplements are sold in several forms. This is what the sources on this page say about them — which form the research used, and any comparison those sources themselves made. Where they made none, this page does not rank the forms.
Ascorbic acid, What the sources supportDetails
ODS, part of the US National Institutes of Health, says ascorbic acid is the most common form in supplements, and that its bioavailability is equivalent to the ascorbic acid in foods such as orange juice and broccoli. The 2013 Cochrane review of colds reports that its trials usually used ascorbic acid tablets. Neither source compared forms for any claim rated below. Source [1]Source [2]
Sodium ascorbate, calcium ascorbate, Ester-C, or ascorbic acid with bioflavonoids, Details
ODS lists these among other forms on sale. It reports that a few human studies compared how they are absorbed. In one, Ester-C and ascorbic acid gave the same blood levels, but Ester-C gave higher levels in white blood cells 24 hours later. Another found no differences in blood levels or urine excretion between ascorbic acid, Ester-C and ascorbic acid with bioflavonoids. Citing these findings and the relatively low cost of ascorbic acid, the authors of that study concluded that simple ascorbic acid is the preferred source. This is about absorption, not about any claim rated below. Source [1]
Reference intake values
Quoted exactly as published by the cited authority. These are population reference values, not a recommendation for you. Ask your doctor or pharmacist what applies to your situation.
Men, 19+ years
- Recommended intake
- 90 mg
- Upper limit
- 2,000 mg
- Source
- Source [1]
Women, 19+ years
- Recommended intake
- 75 mg
- Upper limit
- 2,000 mg
- Source
- Source [1]
Pregnancy, 19+ years
- Recommended intake
- 85 mg
- Upper limit
- 2,000 mg
- Source
- Source [1]
Lactation, 19+ years
- Recommended intake
- 120 mg
- Upper limit
- 2,000 mg
- Source
- Source [1]
What the upper limits count: “The FNB has established ULs for vitamin C that apply to both food and supplement intakes.” Source [1]
Sources
- Vitamin C: Fact Sheet for Health ProfessionalsNIH Office of Dietary Supplements, 2025 · Health authority summary · Primary source
- Vitamin C for preventing and treating the common coldCochrane Database of Systematic Reviews, 2013 · Systematic review · Primary source
- Vitamin C reduces the severity of common colds: a meta-analysisBMC Public Health, 2023 · Meta-analysis · Primary source
- Vitamin C supplementation for the primary prevention of cardiovascular diseaseCochrane Database of Systematic Reviews, 2017 · Systematic review · Primary source · Certainty: very low
- Vitamin, Mineral, and Multivitamin Supplementation to Prevent Cardiovascular Disease and Cancer: US Preventive Services Task Force Recommendation StatementJAMA, 2022 · Health authority summary · Primary source
- Vitamin, Mineral, and Multivitamin Supplementation for the Primary Prevention of Cardiovascular Disease and Cancer: A Systematic Evidence Review for the U.S. Preventive Services Task ForceAgency for Healthcare Research and Quality, 2022 · Systematic review · Primary source
- Effects of vitamin C supplementation on blood pressure: a meta-analysis of randomized controlled trialsThe American Journal of Clinical Nutrition, 2012 · Meta-analysis · Primary source
- What is the evidence that vitamin C supplements lower blood pressure?The American Journal of Clinical Nutrition, 2012 · Published comment · Not counted toward ratings
- Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseasesCochrane Database of Systematic Reviews, 2012 · Meta-analysis · Primary source
Page history
Show all 2 changes to this page
- — Published.
- — First drafted. Scurvy from deficiency rated strong; daily use for shorter, milder colds rated moderate; blood pressure rated limited; daily use to prevent colds in the general population, cardiovascular disease and cancer rated evidence against; starting it once a cold begins and death from any cause rated insufficient.