Vitamin C: what it does, how much you need, and what it will not do

Vitamin C is what people reach for at the first sign of a cold, and that is the one job the evidence says it does least well. The job it really does is quieter. Your body cannot build collagen without it, and collagen is what holds skin, blood vessels and gums together.

What it does in the body

• Vitamin C is required to build collagen, L-carnitine and some neurotransmitters, and acts as an antioxidant and in immune function. Evidence E source

How much you need

• The RDA for vitamin C is 90 mg a day for adult men and 75 mg for adult women. — adults 19+ Evidence E source
• The Tolerable Upper Intake Level for vitamin C is 2,000 mg a day for adults. — adults 19+ Evidence E source
• Five varied servings of fruit and vegetables a day can supply more than 200 mg of vitamin C. Evidence E source
• Sixty milligrams a day puts the median adult at 42 micromoles per litre of plasma vitamin C, and it takes about 100 milligrams to reach the 50 micromole target that European bodies adopted. — adults aged 15 to 65, elderly aged 60 to 96, smokers and non-smokers, in 36 publications Evidence C source
• A third of the vitamin C Americans get arrives in a glass rather than on a plate, which is why storage and processing of drinks matter more for this vitamin than for most. — adults in the United States, What We Eat In America / NHANES 2017-2018 Evidence E source

How well your body absorbs it

• In broccoli, every domestic cooking method tested except steaming caused significant losses of vitamin C. Steaming retained nutrients best. — n/a (food composition study) Evidence D source
• Cooking methods that expose plant foods to high temperature and water for long periods, such as boiling, are the most detrimental to nutrient content, while steaming and microwaving retain water-soluble nutrients better. For some nutrients the research is inconsistent enough that no clear best method can be named. — n/a (review of food composition research) Evidence D source
• The vitamin C in food is reduced by long storage and by cooking, because ascorbic acid dissolves in water and is destroyed by heat. Steaming or microwaving lessens the loss. Evidence E source
• Eating vitamin C-rich fruit with meals raised ferritin by 9.4 micrograms per litre and haemoglobin by 1.34 grams per litre, yet measured iron absorption itself did not change. — females aged 15 to 74 and children; 15 trials, 806 in intervention arms and 575 controls Evidence A source
• The vitamin C on an orange juice label is the number it had on bottling day. Juice made from frozen concentrate lost about a quarter of it after a week in the fridge, and chilled juice lost none. — adults drinking commercial orange juice, both reconstituted from frozen concentrate and ready chilled Evidence B source
• Vitamin C from a tablet, an orange, orange juice and cooked broccoli reached the blood equally well. The one source that fell behind was raw broccoli, by about a fifth. — 68 male non-smokers, each repleted at 108 mg of ascorbic acid a day Evidence B source
• Wrapping vitamin C in fat does raise the peak in the blood: a single 500 mg liposomal dose put 27 percent more into plasma than the same dose of plain vitamin C. — 27 adults, 19 men and 8 women, mean age 36 years Evidence B source
• The advantage of liposomal vitamin C is largest in people who are short of it. In participants who already had normal blood levels, the gap shrank to about 1.3 times. — 10 studies out of 321 screened, doses from 0.15 to 10 g, sampling from 4 to 24 hours Evidence C source
• Nobody has checked whether the extra liposomal vitamin C in the blood stays in the body or goes straight out in the urine. Across all ten studies, none measured what came out. — the 10 pharmacokinetic studies included in the review Evidence C source
• The reviewers who counted the liposomal advantage also gave their verdict on what it is worth: the difference in effect, where anyone measured it, was probably too small to matter. — two of the ten included studies Evidence C source

What too little does

• Signs of scurvy can appear within about a month of intake below roughly 10 mg a day. Evidence E source
• Bleeding gums are a real and reversible sign of low vitamin C: supplements cut the bleeding tendency substantially in people whose blood levels started below 28 micromoles per litre. — predominantly healthy participants in 15 trials across 6 countries, with measured gingival bleeding tendency Evidence A source
• Blood levels high enough to prevent scurvy are not high enough to prevent bleeding: at 11 to 28 micromoles per litre, both bleeding gums and retinal haemorrhage were about half as common again as at higher levels. — US residents in the third National Health and Nutrition Examination Survey with measures of retinal haemorrhaging and gingival bleeding tendency Evidence C source
• Severe vitamin C deficiency can raise pressure in the lung arteries, and in reported cases that pressure fell by more than half once vitamin C was given. — patients of any age in whom vitamin C deficiency was considered the cause of pulmonary hypertension diagnosed by echocardiography or catheterisation; diet was poor in 30 of 32 cases and plasma vitamin C was undetectable in 24 of the 27 measured Evidence C source

Who is most likely to fall short

• People who smoke or are exposed to second-hand smoke are at higher risk of vitamin C inadequacy. — smokers and passive smokers Evidence E source

What the evidence does and does not show

• Taking vitamin C regularly does not reduce the chance of catching a cold in the general population. — general population Evidence A source
• Taking vitamin C regularly shortens colds slightly, by about 8% in adults and 14% in children. — adults and children Evidence A source
• In 29 trial comparisons covering 11,306 people, taking vitamin C every day did not reduce the chance of catching a cold. — general community participants taking at least 0.2 g a day Evidence A source
• Taken every day, vitamin C shortened colds by 8 per cent in adults and 14 per cent in children, across 9,745 cold episodes. — adults and children taking vitamin C regularly, 31 comparisons Evidence A source
• Pooling 15 comparisons from 10 double-blind trials, vitamin C cut the severity of colds by 15 per cent. — healthy people taking at least 1 g a day, 10 trials Evidence A source
• Low mood is not on the confirmed list: across ten randomised trials, vitamin C did nothing measurable to mood. — adults, both depressed and non-depressed, in 10 trials; a subgroup of 5 trials covered people not taking antidepressants Evidence A source
• Vitamin C supplements lower systolic blood pressure by roughly 3.7 mmHg, with no effect on diastolic pressure except in people with diabetes. — adults in trials of vitamin C supplementation; six meta-analyses covering 17 randomised trials reporting blood pressure Evidence A source
• Taking 500 mg of vitamin C a day for up to ten years cut new gout diagnoses by 12 per cent, from 9.1 to 8.0 cases per 1,000 person-years. — male physicians in the Physicians' Health Study II, mean age 64, followed up to ten years; 6.5 per cent already had gout at randomisation Evidence B source
• Genetic evidence in nearly 900,000 people found no causal link between blood vitamin C and the five commonest cancers, and vitamin C supplements showed no benefit for any of them. — 52,018 Europeans in the vitamin C genome-wide association study and up to 870,984 participants of European ancestry in the cancer consortia, covering lung, breast, prostate, colon and rectal cancer Evidence C source
• Each extra 100 milligrams of vitamin C a day from food went with about 11 per cent lower risk of dying from any cause, and the same reviewers say this argues for fruit and vegetables rather than for supplements. — adults in 69 prospective studies reported in 99 publications Evidence C source
• The measured blood level tracks cardiovascular death far more strongly than the reported diet does, which says as much about food questionnaires as about vitamin C. — adults in 15 prospective cohorts and three prospective evaluations within intervention studies Evidence C source
• In a small dose-escalation study, markers of oxidative damage kept falling up to 500 to 1,000 milligrams a day and then stopped, far above the 75 to 90 milligram recommendation. — healthy non-smoking men and women averaging 26 years, recruited from a campus population Evidence B source
• The weakest link in the whole chain is the questionnaire: what people say they eat correlates with their blood vitamin C only moderately, around 0.35 to 0.46. — adults assessed by food frequency questionnaire, dietary recall or diary, and weight records Evidence C source
• There is no approved American health claim linking vitamin C to cancer. The claim that exists is about fruits and vegetables, and it says only that they may contain the vitamin. — marked foods in the United States Evidence E source
• To carry that claim a food has to be a good source of vitamin A, vitamin C or fibre on its own, without anything added. Fortification does not buy the label. — marked foods in the United States Evidence E source
• Intravenous vitamin C did not save lives in covid. Across nine trials and 3345 patients the difference in deaths was nothing, and it was nothing in the critically ill too. — 3345 patients with covid in nine randomised trials, vitamin C given intravenously in all but one, treatment lasting 4 to 14 days Evidence A source

What too much does

• High doses of vitamin C most often cause digestive upset. — adults taking high doses Evidence E source
• High vitamin C intakes may raise urinary oxalate and uric acid, which could contribute to kidney stones. Evidence E source
• In sepsis, intravenous vitamin C improved organ-failure scores and shortened vasopressor use but did not save lives, and it doubled the rate of adverse events. — adults aged 18 and over with sepsis or septic shock, 18 randomised trials Evidence A source
• Vitamin C supplements raise the risk of kidney stones in men and not in women, and the excess is roughly one in eight. — men and women taking ascorbic acid supplements at 250 to over 1500 mg a day, in 4 studies Evidence A source
• In women the same review found no raised stone risk at any dose, from 250 mg up to more than 1500 mg a day. — women taking ascorbic acid supplements in four dose bands Evidence A source
• Two grams of vitamin C a day pushed up urinary oxalate and the calculated stone risk in four out of ten people, whether or not they had ever had a stone. — 29 stone formers and 19 age- and sex-matched non-stone formers on a controlled low-oxalate diet Evidence B source
• At intravenous doses, vitamin C has actually harmed people: in the largest sepsis trial, more patients on vitamin C died or stayed on life support than on placebo. — adults in intensive care for no more than 24 hours with proven or suspected infection and receiving a vasopressor Evidence B source

Medicines it interacts with

• People having chemotherapy or radiation should ask their oncologist before taking vitamin C supplements, especially in high doses. — people in cancer treatment Evidence E source

What to do with this

Before you change anything, work out whether this page is about you. If fruit and vegetables appear on your plate most days in any form, your vitamin C is handled and nothing here needs acting on.

Two situations change that. Smoking, including living with a smoker, raises what you need. And a diet that has narrowed down to the same few cooked dishes, which happens to people during hard months more often than anyone admits, can drift low without any dramatic signs.

If either applies, the fix is one raw thing a day placed where you will actually eat it. A clementine in a bag, pepper strips beside lunch, fruit on yogurt. Keep it raw where you can, steam or roast rather than boil where you cannot, and save the cooking water for the sauce.

If you take a vitamin C tablet, the size of it matters more than the habit. A few hundred milligrams with food does what a gram does. Two grams a day, which is the stated ceiling, raised the oxalate in the urine of four people out of ten inside a week, and men taking supplements were found to get more kidney stones than women taking the same ones. If you have ever passed a stone, that is a question for your doctor before it is a question of dose.

Where to get it from food

The bottom line

If you eat fruit and vegetables regularly you are almost certainly getting enough, and more is not better. Two groups are worth a second look: people who smoke, and people whose diets have very little variety. Taking vitamin C to avoid catching colds does not work. Taking it once a cold has started shortens the cold by a matter of hours rather than days. Several results have landed since this page was written, and the useful ones are about dose. The level that prevents scurvy and the level that stops small bleeds are not the same. Plasma between 11 and 28 micromoles per litre keeps scurvy away, and people sitting in that range had about half again as much gum and retinal bleeding as people above it. Supplements cut gum bleeding sharply in anyone who started below 28 and did almost nothing in anyone above 48. What an intake does to a blood level also varies more than a label admits. Sixty milligrams a day puts younger adults at 44 micromoles, older people at 31 and smokers at 34. Reaching the 50 that European bodies settled on takes about 100. On supplements at high dose the news is poor in two places. Men taking them had about 60 per cent higher odds of kidney stones than women, who showed no raised risk at any dose tested, and two grams a day raised urinary oxalate in four people out of ten within a week. In intensive care, the largest trial of intravenous vitamin C left more patients dead or on organ support than placebo, a risk ratio of 1.21, against pooled smaller trials that had moved an organ-failure score and nothing else. What survives on the benefit side is modest and worth having. Blood pressure falls by roughly 3.7 mmHg with low certainty, 500 milligrams a day cut new gout diagnoses in male physicians by 12 per cent, and genetic evidence in nearly 900,000 people found no causal link to the five commonest cancers. Adding vitamin C rich fruit to meals raised ferritin and haemoglobin a little while measured iron absorption did not move. One caution runs under all the cohort numbers here. What people report eating agrees with the vitamin C in their blood only moderately, around 0.35 to 0.46. The newest batch of evidence lands on the two things people actually buy. Liposomal vitamin C does raise the peak in the blood, by 27 per cent after a single 500 mg dose, and the advantage shrinks to about 1.3 to 1.4 times in people whose level was normal to begin with. Across all ten studies of it, none measured how much left in the urine, only two looked at cells and only two measured any biological effect, and the reviewers call the clinical significance likely to be minimal. Intravenous vitamin C in covid is a plain null: nine trials, 3,345 patients, no difference in deaths overall or in the critically ill. On the food side, what survives cooking is absorbed as well as a tablet, and only raw broccoli lagged, by a fifth. Juice is where the number slips, since orange juice from frozen concentrate fell from 117 to 89 mg per 8 fl oz after a week in the fridge while chilled juice held. A third of the vitamin C Americans take in comes from drinks, which is why that matters. And no American health claim links vitamin C to cancer: the authorised claim is about fruit and vegetables, and a food has to be a good source without fortification to carry it.

Sources

1. vitc-01 · Position of an expert body · expert body statement
   Vitamin C is required for the biosynthesis of collagen, L-carnitine, and certain neurotransmitters; vitamin C is also involved in protein metabolism.
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin C · checked 2026-09-15 · extracted
2. vitc-02 · Position of an expert body · expert body recommendation
   RDA for adults: 90 mg for males 19+; 75 mg for females 19+ (value from the source's table, not a sentence)
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin C · checked 2026-09-15 · independently re-checked
3. vitc-03 · Position of an expert body · expert body recommendation
   UL for adults 19+: 2,000 mg (value from the source's table, not a sentence)
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin C · checked 2026-09-15 · independently re-checked
4. vitc-12 · Position of an expert body · expert body statement
   Consuming five varied servings of fruits and vegetables a day can provide more than 200 mg of vitamin C.
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin C · checked 2026-09-16 · extracted
5. vitc-r5-1 · Observational data · meta-analysis of intake and plasma concentration data
   The 50th percentile of the plasma concentration for a daily vitamin C intake of 60 mg was 42.4 mumol/L. The corresponding values for the different subgroups were: "adult" 44.1 mumol/L, "elderly" 31.0 mumol/L, "nonsmokers" 42.4 mumol/L, and "smokers" 33.6 mumol/L.
   Brubacher et al., International Journal for Vitamin and Nutrition Research, 2000 · checked 2026-09-17 · independently re-checked
6. vitc-e3-02 · Position of an expert body · cross-sectional dietary survey brief
   Beverages also contributed large amounts to daily intakes of select vitamins and minerals including one-third of vitamin C intake and approximately ¼ of the intake of vitamin D, calcium, potassium and magnesium.
   FSRG Dietary Data Briefs, USDA Agricultural Research Service, WWEIA/NHANES 2017-2018 · checked 2026-09-18 · independently re-checked
7. vitc-13 · Mechanistic or laboratory data · food composition experiment, five cooking methods
   The results show that all cooking treatments, except steaming, caused significant losses of chlorophyll and vitamin C and significant decreases of total soluble proteins and soluble sugars.
   Yuan G-F et al. Effects of different cooking methods on health-promoting compounds of broccoli. J Zhejiang Univ Sci B. 2009 Aug;10(8):580-8. · checked 2026-09-16 · extracted
8. vitc-14 · Mechanistic or laboratory data · narrative review
   Cooking methods that expose plant foods to high temperatures and/or water for long periods of time (e.g. boiling) may be the most detrimental to nutrient content, whereas other cooking methods such as steaming or microwaving may help to retain nutrients, particularly those that are water-soluble.
   Nutrition Bulletin. Cooking at home to retain nutritional quality and minimise nutrient losses: A focus on vegetables, potatoes and pulses. 2022 Dec;47(4):538-562. · checked 2026-09-16 · extracted
9. vitc-11 · Position of an expert body · expert body statement
   The vitamin C content of food may be reduced by prolonged storage and by cooking because ascorbic acid is water soluble and is destroyed by heat. Steaming or microwaving may lessen cooking losses.
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin C · checked 2026-09-16 · extracted
10. vitc-r3-04 · Meta-analysis or systematic review · systematic review and meta-analysis of trials
    Including ascorbate-rich fruits in meals had a positive impact on serum ferritin [7 trials, n = 762; mean difference (MD) = 9.39 μg/L; P < 0.001; moderate certainty], hemoglobin (12 trials, n = 1141; MD = 1.34 g/L; P = 0.01; moderate certainty), serum transferrin receptor (6 studies; MD = -0.37 mg/L; P < 0.001; high certainty), and iron balance (1 trial; MD = 2.4; low certainty)...No impact on iron absorption (3 studies; MD = 3.36%; P = 0.07, low certainty), plasma ferritin (4 studies; MD = -0.11 μg/L, P = 0.82; high certainty), or plasma transferrin receptor (3 studies; MD = 1.53 mg/L; very low certainty).
    American Journal of Clinical Nutrition, 2026 · checked 2026-09-17 · independently re-checked
11. vitc-e3-01 · Randomised controlled trial(s) · randomised crossover trial
    The ascorbic acid content decreased significantly after storage in juice reconstituted from frozen concentrate (117+/-8 vs 89+/-8 mg/8 fl oz, P =.001), but did not change in chilled juice (69+/-5 vs 64+/-12 mg/8 fl oz.).
    Johnston et al., Journal of the American Dietetic Association, 2005 · checked 2026-09-18 · independently re-checked
12. vitc-e3-03 · Randomised controlled trial(s) · randomised controlled depletion and repletion trial
    Ascorbic acid ingested as cooked broccoli, orange juice or fruit, or in synthetic form seems to be equally bioavailable. The lower relative bioavailability of ascorbic acid from raw broccoli is unlikely to be of practical importance in mixed diets.
    Mangels et al., Journal of Nutrition, 1993 · checked 2026-09-18 · independently re-checked
13. vitc-e3-04 · Randomised controlled trial(s) · randomised double-blind crossover trial
    Additionally, LV-VIT C had significantly higher Cmax (plasma + 27%, leukocytes + 20%, p < 0.001) and AUC0 - 24 (plasma + 21%, leukocytes + 8%, p < 0.001) values as compared to VIT C.
    European Journal of Nutrition, 2024 · checked 2026-09-18 · independently re-checked
14. vitc-e3-05 · Observational data · scoping review of pharmacokinetic studies
    In contrast, studies in which the participants had adequate vitamin C status at baseline (means approximately 50 μmol/L) had much smaller differences between the non-liposomal and liposomal AUCs (e.g., 1.3- to 1.4-fold)
    Carr et al., Basic & Clinical Pharmacology & Toxicology, 2025 · checked 2026-09-18 · independently re-checked
15. vitc-e3-06 · Observational data · scoping review of pharmacokinetic studies
    None of the studies reported ascorbate elimination over the sampling period.
    Carr et al., Basic & Clinical Pharmacology & Toxicology, 2025 · checked 2026-09-18 · independently re-checked
16. vitc-e3-07 · Observational data · scoping review of pharmacokinetic studies
    The clinical significance of these small percentage differences is uncertain and likely to be minimal.
    Carr et al., Basic & Clinical Pharmacology & Toxicology, 2025 · checked 2026-09-18 · independently re-checked
17. vitc-04 · Position of an expert body · expert body statement
    The timeline for the development of scurvy varies, depending on vitamin C body stores, but signs can appear within 1 month of little or no vitamin C intake (below about 10 mg/day).
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin C · checked 2026-09-15 · independently re-checked
18. vitc-r2-1 · Meta-analysis or systematic review · systematic review and meta-analysis of controlled trials
    In clinical trials, AA supplementation reduced gingival bleeding tendency when estimated baseline AA plasma levels were < 28 μmol/L (standardized mean difference [SMD], -0.83; 95%CI, -1.16 to -0.49; P < 0.002).
    Hujoel et al., Nutrition Reviews, 2021 · checked 2026-09-17 · independently re-checked
19. vitc-r2-2 · Observational data · cross-sectional survey analysis
    In NHANES III, prevalence of both retinal hemorrhaging and gingival bleeding tendency increased when AA plasma levels were within the range that protects against scurvy (11-28 μmol/L; respective prevalence ratios adjusted for age and sex: 1.47; 95%CI: 1.22-1.77; and 1.64; 95%CI: 1.32-2.03; P < 0.001 for both).
    Hujoel et al., Nutrition Reviews, 2021 · checked 2026-09-17 · independently re-checked
20. vitc-r2-3 · Observational data · systematic review of case reports
    During periods of vitamin C deficiency, the median mPAP was 48 mmHg (range 29-77 mmHg; N = 28). After the start of vitamin C administration, the median mPAP was 20 mmHg (range 12-33 mmHg; N = 18). For the latter 18 cases, mPAP was 2.4-fold (median) higher during vitamin C deficiency.
    Hemilä & de Man, BMC Pulmonary Medicine, 2024 · checked 2026-09-17 · independently re-checked
21. vitc-09 · Position of an expert body · expert body statement
    People who smoke and those exposed to secondhand smoke (value from the source's table, not a sentence)
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin C · checked 2026-09-15 · extracted
22. vitc-05 · Meta-analysis or systematic review · Cochrane review (2007) of placebo-controlled trials using ≥200 mg/day
    Prophylactic use of vitamin C did not significantly reduce the risk of developing a cold in the general population.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin C · checked 2026-09-15 · independently re-checked
23. vitc-06 · Meta-analysis or systematic review · Cochrane review (2007) of placebo-controlled trials using ≥200 mg/day
    In the general population, the use of prophylactic vitamin C modestly reduced cold duration by 8% in adults and 14% in children.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin C · checked 2026-09-15 · independently re-checked
24. cold-c1 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis
    In the general community trials involving 10,708 participants, the pooled RR was 0.97 (95% confidence interval (CI) 0.94 to 1.00).
    Hemilä and Chalker, Cochrane Database of Systematic Reviews, 2013 · checked 2026-09-16 · independently re-checked
25. cold-c3 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis
    In adults the duration of colds was reduced by 8% (3% to 12%) and in children by 14% (7% to 21%). In children, 1 to 2 g/day vitamin C shortened colds by 18%.
    Hemilä and Chalker, Cochrane Database of Systematic Reviews, 2013 · checked 2026-09-16 · independently re-checked
26. cold-c5 · Meta-analysis or systematic review · meta-analysis of randomised trials
    Compared to placebo, vitamin C significantly decreased the severity of the common cold by 15% (95% CI 9-21%).
    Hemilä, BMC Public Health, 2023 · checked 2026-09-16 · independently re-checked
27. vitc-r2-4 · Meta-analysis or systematic review · systematic review and meta-analysis of randomised trials
    Finding from 10 trials with 836 participants revealed no significant improvement in mood status in overall analysis (n = 10, Hedge's g = 0.09; 95% confidence interval: -0.15 to 0.33; P = 0.465).
    Yosaee et al., General Hospital Psychiatry, 2021 · checked 2026-09-17 · independently re-checked
28. vitc-r3-01 · Meta-analysis or systematic review · umbrella review of meta-analyses of randomised trials
    The findings suggest that vitamin C supplementation may reduce SBP by approximately 3.7 mmHg. Although DBP did not decrease overall, a clinically important reduction was observed in patients with diabetes (-2.27 mmHg).
    Food & Function, 2026 · checked 2026-09-17 · independently re-checked
29. vitc-r3-03 · Randomised controlled trial(s) · post hoc analysis of a randomised double-blind placebo-controlled trial
    The incidence rate of new gout diagnoses during follow-up was 8.0 per 1000 person-years among those assigned vitamin C compared with 9.1 per 1000 person-years among those assigned placebo. The vitamin C assignment reduced new gout diagnoses by 12% (HR: 0.88; 95% CI: 0.77, 0.99; P = 0.04).
    American Journal of Clinical Nutrition, 2022 · checked 2026-09-17 · independently re-checked
30. vitc-r3-05 · Observational data · Mendelian randomisation study with meta-analysis of cohorts and trials
    The MR analysis showed no evidence of a causal association of circulating vitamin C concentration with any examined cancer...Moreover, our MR results were consistent with the null findings from the meta-analysis exploring prospective associations of dietary or supplemental vitamin C intakes with cancer risk, except that higher dietary vitamin C intake, but not vitamin C supplement, was associated with a lower risk of lung cancer (risk ratio: 0.84, 95% confidence interval 0.71 to 0.99).
    BMC Medicine, 2021 · checked 2026-09-17 · independently re-checked
31. vitc-r5-2 · Observational data · dose-response meta-analysis of prospective studies
    The summary RR per 100-mg/d increment of dietary vitamin C intake was 0.88 (95% CI: 0.79, 0.98, I2 = 65%, n = 11) for coronary heart disease, 0.92 (95% CI: 0.87, 0.98, I2 = 68%, n = 12) for stroke, 0.89 (95% CI: 0.85, 0.94, I2 = 27%, n = 10) for cardiovascular disease, 0.93 (95% CI: 0.87, 0.99, I2 = 46%, n = 8) for total cancer, and 0.89 (95% CI: 0.85, 0.94, I2 = 80%, n = 14) for all-cause mortality.
    Aune et al., American Journal of Clinical Nutrition, 2018 · checked 2026-09-17 · independently re-checked
32. vitc-r5-3 · Observational data · dose-response meta-analysis of prospective observational studies
    The relative risks of CVD mortality for the highest v. the lowest category of antioxidant intakes were as follows: vitamin C, 0·79 (95 % CI 0·68, 0·89; I 2=46 %, n 10); vitamin E, 0·91 (95 % CI 0·79, 1·03; I 2=51 %, n 8); β-carotene, 0·89 (95 % CI 0·73, 1·05; I 2=34 %, n 4). The relative risks for circulating concentrations were: vitamin C, 0·60 (95 % CI 0·42, 0·78; I 2=65 %, n 6)
    Jayedi et al., Public Health Nutrition, 2019 · checked 2026-09-17 · independently re-checked
33. vitc-r5-4 · Randomised controlled trial(s) · controlled clinical trial
    Plasma vitamin C rose 55% in vitamin C-supplemented subjects by the end of the ten-week treatment (p < 0.05), and measures of oxidative stress decreased 60% to 90% (8.1 +/- 0.6 to 3.5 +/- 0.4 nmol/mL and 69.1 +/- 7.8% to 6.7 +/- 6.0% for total lipid hydroperoxides and Heinz bodies, respectively).
    Johnston and Cox, Journal of the American College of Nutrition, 2001 · checked 2026-09-17 · independently re-checked
34. vitc-r5-5 · Observational data · meta-analysis of validation studies
    The overall result of this study showed a positive correlation coefficient between Food Frequency Questionnaire (FFQ) and biomarker (r = 0.35 for "both" genders, 0.39 for females, and 0.46 for males). Also the correlation between Dietary Recalls (DR)/diary and biomarker was 0.46 for "both" genders, 0.44 for females, and 0.36 for males.
    Dehghan et al., Nutrition Journal, 2007 · checked 2026-09-17 · independently re-checked
35. vitc-e3-08 · Position of an expert body · federal regulation, authorised health claim
    Development of cancer depends on many factors. Eating a diet low in fat and high in fruits and vegetables, foods that are low in fat and may contain vitamin A, vitamin C, and dietary fiber, may reduce your risk of some cancers.
    21 CFR 101.78, дозволена заява про здоровʼя «фрукти й овочі та рак» · checked 2026-09-18 · independently re-checked
36. vitc-e3-09 · Position of an expert body · federal regulation, authorised health claim
    The food shall meet, without fortification, the nutrient content requirements of § 101.54 for a “good source” of at least one of the following: vitamin A, vitamin C, or dietary fiber.
    21 CFR 101.78, дозволена заява про здоровʼя «фрукти й овочі та рак» · checked 2026-09-18 · independently re-checked
37. vitc-e3-10 · Meta-analysis or systematic review · systematic review and meta-analysis of randomised controlled trials
    The pooled analysis showed that vitamin C administration was associated with no significant difference in all-cause mortality in COVID-19 patients when compared to the standard treatment (RR 0.92, 95% CI: 0.83–1.02; I2 = 1%)
    Annals of Medicine and Surgery, 2026 · checked 2026-09-18 · independently re-checked
38. vitc-07 · Position of an expert body · expert body statement
    The most common complaints are diarrhea, nausea, abdominal cramps, and other gastrointestinal disturbances.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin C · checked 2026-09-15 · extracted
39. vitc-08 · Position of an expert body · expert body statement
    high vitamin C intakes also have the potential to increase urinary oxalate and uric acid excretion, which could contribute to the formation of kidney stones.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin C · checked 2026-09-15 · extracted
40. vitc-r3-02 · Meta-analysis or systematic review · meta-analysis of randomised trials
    There were significant effects in the delta SOFA score from baseline to 72-96 h (MD, - 0.62; 95% CI, - 1.00 to - 0.25; p = 0.001) and the duration of vasopressor use (MD, - 15.07; 95% CI, - 21.59 to - 8.55; p < 0.00001) with IVVC therapy. Treatment with IVVC was not shown to improve short-term mortality (OR, 0.89; 95% CI, 0.77 to 1.04; p = 0.14); nevertheless, dose at 25-100 mg/kg/d subgroup associated with a significant reduction in short-term mortality (OR, 0.80; 95% CI, 0.65 to 0.97; p = 0.03). An increase adverse event was observed in IVVC therapy (OR, 1.98; 95% CI, 1.06 to 3.68; p = 0.03).
    Critical Care, 2023 · checked 2026-09-17 · independently re-checked
41. vitc-r6-01 · Meta-analysis or systematic review · systematic review and meta-analysis of observational studies
    The kidney stones incidence was significantly higher in men than women with AA supplements (OR= 1.62; 95% CI: 1.09 to 2.42; P=0.02). AA supplements (250-499mg/d, 1000-1499mg/d) was remarkably correlated with the risk of renal stones among men (OR= 1.14, 95% CI: 1.00 to 1.28, P=0.04; OR= 1.12, 95% CI: 1.11 to 1.13, P<0.00001; respectively).
    Jiang et al., Urology Journal, 2019 · checked 2026-09-17 · independently re-checked
42. vitc-r6-02 · Meta-analysis or systematic review · systematic review and meta-analysis of observational studies
    In addition, AA supplements (250-499mg/d, 500-999mg/d, 1000-1499mg/d, >1500mg/d) did not remarkably correlate with the risk of renal stones among women (OR= 1.00, 95% CI: 0.82 to 1.22, P=0.98; OR= 1.08, 95% CI: 0.99 to 1.18, P=0.09; OR= 0.99, 95% CI: 0.90 to 1.08, P=0.77; OR= 0.99, 95% CI: 0.99 to 1.09, P=0.88; respectively).
    Jiang et al., Urology Journal, 2019 · checked 2026-09-17 · independently re-checked
43. vitc-r6-03 · Randomised controlled trial(s) · randomised crossover controlled feeding trial
    Of the 48 participants, 19 (12 stoneformers, 7 non-stoneformers) were identified as responders, defined by an increase in 24-h total oxalate excretion > 10% after treatment A compared with N. ... The 1000 mg AA twice each day increased urinary oxalate and TRI for calcium oxalate kidney stones in 40% of participants, both stoneformers and non-stoneformers.
    Traxer et al., Journal of Nutrition, 2005 · checked 2026-09-17 · independently re-checked
44. vitc-r6-04 · Randomised controlled trial(s) · randomised controlled trial
    The primary outcome occurred in 191 of 429 patients (44.5%) in the vitamin C group and in 167 of 434 patients (38.5%) in the control group (risk ratio, 1.21; 95% confidence interval [CI], 1.04 to 1.40; P = 0.01). At 28 days, death had occurred in 152 of 429 patients (35.4%) in the vitamin C group and in 137 of 434 patients (31.6%) in the placebo group (risk ratio, 1.17; 95% CI, 0.98 to 1.40)
    Lamontagne et al., New England Journal of Medicine, 2022 · checked 2026-09-17 · independently re-checked
45. vitc-10 · Position of an expert body · expert body statement
    individuals undergoing these procedures should consult with their oncologist prior to taking vitamin C or other antioxidant supplements, especially in high doses.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Vitamin C · checked 2026-09-15 · extracted