MVIIIHealth The MVIII app
← Back

Research · Supplements

Vitamin C

Vitamin C did not change how often people caught colds except under heavy physical stress, where colds halved. Adult colds were 8% shorter. Blood pressure fell 3.8 mm Hg in short trials. Heart events, cancer incidence and COVID-19 deaths did not change. Men on 1,000 mg or more had more kidney stones. Three critical care trials found worse outcomes on intravenous doses.

Add to Bio HackChecked 2026-11-12
Status
Dietary supplement in the US. Intravenous ascorbic acid is a prescription drug.
Also called
ascorbic acid, ascorbate, sodium ascorbate, calcium ascorbate, liposomal vitamin C, Ester-C, Emergen-C, IV vitamin C
Taken for
immunity, preventing colds, shorter colds, COVID-19, recovery, muscle soreness, blood pressure, heart health, cancer prevention, cancer treatment, sepsis, skin, skin aging, wrinkles, antioxidant, bleeding gums, gum disease, periodontitis

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help4

Reported risks3

What people take it for, and what was found

Shown to help4

Moderate

Blood pressure

Shown to lower blood pressure about 3.8 mmHg systolic and 1.5 mmHg diastolic in short trials of adults.

The numbers and sources
Effect
Across 29 trials, systolic pressure fell 3.84 mm Hg (95% CI 2.38 to 5.29) and diastolic 1.48 mm Hg (95% CI 0.10 to 2.86) against control. In people with hypertension, systolic fell 4.85 mm Hg, and the diastolic change of 1.67 mm Hg was not significant [2].
Population
Trials of 10 to 120 participants, median dose 500 mg a day, median 8 weeks [2].
Sources
[2]
Caveats
Short trials of blood pressure, not of heart attack or stroke. Effects shrank when 9 trials with imputed data were added [2].
Moderate

Survival with cancer (intravenous)

Intravenous vitamin C was linked to longer survival in adults with cancer, with larger effects in cohort studies than in trials. Progression-free survival did not differ.

The numbers and sources
Effect
Intravenous vitamin C was associated with longer median overall survival than no vitamin C (median survival ratio 1.83, 95% CI 1.40 to 2.40). Progression-free survival did not significantly differ (ratio 1.80, 95% CI 0.95 to 3.41) [6].
Population
8 RCTs and cohort studies with 2,722 adults with cancer, given 2.5 g a day to 1.5 g per kg a day for 9 days to 1 year [6].
Sources
[6]
Caveats
The review pooled cohort studies with RCTs, and the survival ratio was larger in cohort studies than in RCTs. It was also larger at doses under 1 g per kg and without chemotherapy. The authors rated the certainty moderate [6]. This describes intravenous treatment, not oral supplements.
Moderate

Bleeding gums

Shown to lower gum bleeding in mostly healthy people, most in those with low vitamin C levels, and only slightly when levels were already high.

The numbers and sources
Effect
Across 15 trials (1,140 mostly healthy participants), vitamin C lowered gingival bleeding tendency when estimated baseline plasma vitamin C was below 28 µmol/L (SMD -0.83, 95% CI -1.16 to -0.49). When baseline levels were above 48 µmol/L the effect was small (SMD -0.23, 95% CI -0.45 to -0.01), and when unknown it was not significant (SMD -0.56, 95% CI -1.19 to 0.06) [7]. A systematic review of 6 RCTs found vitamin C improved bleeding indices in gingivitis [8]. In 136 children aged 8 to 16 given scaling and oral hygiene instruction, adding vitamins C and D for 8 weeks gave a lower percentage of bleeding sites at 4 and 8 weeks, after adjusting for a higher starting level in that group [9].
Population
1,140 mostly healthy participants in 6 countries [7]; adults in RCTs of periodontal therapy [8]; school children in Pakistan [9].
Sources
[7], [8], [9]
Caveats
The effect depended on starting vitamin C status [7]. The children's trial combined vitamins C and D, had no placebo, and its groups differed at baseline [9].
LimitedStudied in women

Skin aging and wrinkles, oral

Limited evidence: higher dietary vitamin C was linked to a lower chance of a wrinkled appearance in 4,025 women. No supplement trial was located.

Compared with women with lower vitamin C intakes in the same survey [28]

The numbers and sources
Effect
In 4,025 US women aged 40 to 74, higher vitamin C intake was linked to lower odds of a wrinkled appearance (OR 0.89, 95% CI 0.82 to 0.96) and of senile dryness (OR 0.93, 95% CI 0.87 to 0.99), judged by dermatologists. The links held after adjusting for age, race, education, sun exposure, income, menopause, BMI, supplement use, activity and energy intake [28].
Population
4,025 women in the first US National Health and Nutrition Examination Survey, with intake from one 24-hour recall [28]. Observational.
Sources
[28]
Caveats
Cross-sectional, with diet measured on one day, so it cannot show cause and confounding may remain. It describes vitamin C from the whole diet, not supplements [28].

Mixed results3

Moderate

Catching colds and how long they last

Not shown to prevent colds in the general population, though colds were 8% shorter in adults. Risk halved in people under heavy physical stress.

The numbers and sources
Effect
In general community trials, regular vitamin C did not change the risk of catching a cold (RR 0.97, 95% CI 0.94 to 1.00). In marathon runners, skiers and soldiers on subarctic exercises, the risk halved (RR 0.48, 95% CI 0.35 to 0.64). Regular supplementation shortened colds by 8% in adults (95% CI 3% to 12%) and 14% in children. Taken only once a cold had started, vitamin C showed no consistent effect on duration or severity [1].
Population
29 trial comparisons with 11,306 participants for incidence, 10,708 of them in community trials and 598 under heavy physical stress. 31 comparisons covering 9,745 cold episodes for duration [1].
Sources
[1]
Caveats
Trials used at least 0.2 g a day. The therapeutic trials were few, 7 comparisons [1].
Limited

Muscle soreness after exercise

Limited evidence: antioxidant supplements lowered soreness slightly up to 72 hours after exercise, in trials mostly at high risk of bias, not specific to vitamin C.

The numbers and sources
Effect
Across 50 trials of antioxidant supplements, soreness was slightly lower up to 6 hours (SMD -0.30), at 24 hours (SMD -0.13, 95% CI -0.27 to 0.00), 48 hours (SMD -0.24) and 72 hours (SMD -0.19). At 96 hours there was little difference [12].
Population
1,089 participants aged 16 to 55, 88% male, in trials of several kinds of antioxidant supplements and antioxidant-rich foods [12].
Sources
[12]
Caveats
Not specific to vitamin C. 47 of 50 trials carried a high risk of bias, and all used doses above the daily amount set for the general population [12].
Limited

Sunburn sensitivity, oral

Small trials found vitamin C with vitamin E slightly raised the UV dose needed for sunburn, while vitamin C alone did not change UV redness.

The numbers and sources
Effect
In 10 people, 2 g of vitamin C with 1,000 IU of vitamin E a day for 8 days raised the median UV dose needed for sunburn from 80 to 96.5 mJ/cm² (p < 0.01), while it fell from 80 to 68.5 mJ/cm² on placebo [14]. In 12 volunteers, 500 mg of vitamin C a day for 8 weeks raised skin vitamin C and did not change the redness response to UV [15]. A systematic review of 47 photoprotection studies found the weakest evidence for isolated vitamin or CoQ10 supplements [16].
Population
10 adults [14]; 12 healthy volunteers [15]; human studies [16].
Sources
[14], [15], [16]
Caveats
The positive trial combined vitamins C and E, so vitamin C's share is unknown [14]. The vitamin C only abstract describes no placebo group [15]. Both are small and short.

Not shown to help5

Moderate

COVID-19

Not shown to lower death, ventilation or hospital stay in patients with COVID-19 in randomized trials. A review adding cohort studies found lower mortality.

The numbers and sources
Effect
Across 9 RCTs, vitamin C did not change death from any cause (RR 0.92, 95% CI 0.83 to 1.02), need for ventilation (RR 0.98, 95% CI 0.87 to 1.11) or length of hospital stay (MD -0.63 days, 95% CI -3.04 to 1.78) [3]. Across 13 studies, short-term mortality (RR 0.92, 95% CI 0.72 to 1.17) and in-hospital mortality (RR 1.05, 95% CI 0.95 to 1.16) did not change [4]. A review that also pooled cohort and retrospective studies found lower mortality (OR 0.64, 95% CI 0.51 to 0.80) [5].
Population
Patients with COVID-19, 9 RCTs [3]; 13 studies with 12,062 participants [4]; 22 studies with 3,429 hospitalized patients [5].
Sources
[3], [4], [5]
Caveats
Sources disagree. The review that found lower mortality pooled cohort and retrospective studies [5]. Certainty ranged from very low to moderate [4].
Moderate

Periodontitis, added to dental treatment

Not shown to improve gum pocket depth or attachment when added to periodontal treatment in adults with periodontitis.

The numbers and sources
Effect
In a systematic review of 6 RCTs, vitamin C added to nonsurgical periodontal therapy did not significantly reduce probing depth or increase clinical attachment at 3 months [8].
Population
Adults 18 and older with periodontitis [8].
Sources
[8]
Caveats
Six trials, assessed with a quality appraisal tool and not pooled. The authors describe the evidence as limited [8].
LimitedStudied in men

Heart attack, stroke and cardiovascular death

One trial found no change in heart attack, stroke or cardiovascular death over 8 years in male physicians aged 50 or older.

The numbers and sources
Effect
Over 8 years, major cardiovascular events did not differ on 500 mg a day against placebo (HR 0.99, 95% CI 0.89 to 1.11). Heart attack, stroke and cardiovascular death each did not differ [10].
Population
14,641 US male physicians aged 50 or older in the Physicians' Health Study II [10].
Sources
[10]
Caveats
One trial, men only.
Why limited
This rests on one trial, of 14,641 people. Strength counts independent studies that agree, so one trial is limited at any size.
LimitedStudied in men

Cancer

One trial found no change in total, prostate, colorectal or lung cancer over 8 years in male physicians.

The numbers and sources
Effect
Total cancer did not differ on vitamin C against placebo (17.6 and 17.5 per 1,000 person-years, HR 1.01, 95% CI 0.92 to 1.10), nor did prostate, colorectal or lung cancer [11].
Population
The same 14,641 men, mean follow-up 8.0 years [11].
Sources
[11]
Caveats
One trial, men only.
Why limited
This rests on one trial, of 14,641 people. Strength counts independent studies that agree, so one trial is limited at any size.
Limited

Training adaptation

One trial found muscle mitochondrial markers rose with endurance training on placebo but not with vitamin C plus E. VO2max rose 8% in both groups.

The numbers and sources
Effect
Over 11 weeks of endurance training, VO2max rose 8% with vitamin C plus E and 8% with placebo. Markers of mitochondrial growth in muscle rose on placebo (COX4 59%, PGC-1α 19%) but not with the vitamins (-13% and -13%) [13].
Population
54 young men and women given 1,000 mg vitamin C and 235 mg vitamin E a day [13].
Sources
[13]
Caveats
One trial of a combination, so the result cannot be assigned to vitamin C alone. Performance did not differ between groups. Funders included Sana Pharma AS and Smartfish AS [13].

Doses studied

Cold trials used 0.2 g a day or more, with 1 to 2 g a day in some child trials [1]. Blood pressure trials had a median of 500 mg a day [2]. The Physicians' Health Study II used 500 mg a day [10][11]. The training trial used 1,000 mg a day [13]. The sepsis trial gave 50 mg per kg intravenously every 6 hours for up to 96 hours [17], as did the burn trial [18]. The cardiac arrest trial gave 3 g or 10 g intravenously a day for 96 hours [19]. Intravenous cancer studies used 2.5 g a day to 1.5 g per kg a day [6]. EFSA found no adequate data to derive a tolerable upper intake level for vitamin C [20]. The sunburn trials used 2 g of vitamin C with 1,000 IU of vitamin E a day for 8 days [14] and 500 mg of vitamin C a day for 8 weeks [15].

Risks

Reported risks3

LimitedHow often is not known

Kidney stones in men

Linked to about 43% more kidney stones in men with intake of 1,000 mg a day or more. No link appeared in women.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In men, total vitamin C intake of 1,000 mg a day or more was associated with more kidney stones than intake under 90 mg (HR 1.43, 95% CI 1.15 to 1.79). Supplements of 1,000 mg or more were associated with an HR of 1.19 (95% CI 1.01 to 1.40). No association appeared in women, or for vitamin C from food [21].
Population
156,735 women and 40,536 men in US cohorts, median follow-up 11.3 to 11.7 years, 6,245 stones [21].
Sources
[21], [22]
Caveats
Observational, intake from food questionnaires, and stone type was not known for every case [21]. A 2026 meta-analysis of 9 interventional studies found that vitamin C supplements raised 24-hour urinary oxalate by 6.45 mg against placebo, in people with and without past stones. Urinary citrate and calcium did not change. Urinary oxalate is a stone risk factor, not a count of stones [22].
ModerateHow often is not known

Intravenous vitamin C in critical illness

Shown to raise death or organ dysfunction with intravenous vitamin C in sepsis, and deaths in severe burns. This concerns critically ill patients, not oral supplements.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In sepsis, death or persistent organ dysfunction at 28 days occurred in 44.5% on intravenous vitamin C and 38.5% on placebo (RR 1.21, 95% CI 1.04 to 1.40). One patient had severe low blood sugar and another a serious anaphylaxis event [17]. In severe burns, 28-day mortality was 15.0% on vitamin C and 7.6% on placebo (adjusted RR 1.96, 95% CI 1.32 to 2.90), and the trial was stopped early for futility or harm [18]. After cardiac arrest, organ function improved 2.5 points less on 10 g a day than on placebo (95% CI 0.5 to 4.5), with more troponin release, worse kidney function and worse neurological outcomes [19]. Pooled across 14 sepsis trials, 28-day mortality was lower on vitamin C (RR 0.70, 95% CI 0.53 to 0.93), but the difference came from single-center trials and did not appear in multicenter trials [23].
Population
872 adults in intensive care with sepsis receiving vasopressors [17]; 238 adults with burns over 20% or more of the body at 24 centers [18]; 273 comatose adults after out-of-hospital cardiac arrest [19]; 14 RCTs with 1,958 patients with sepsis [23].
Sources
[17], [18], [19], [23]
Caveats
Intravenous doses in critically ill patients, in three different conditions. This does not describe oral supplements in healthy people. The burn trial's primary composite did not reach significance (RR 1.28, 95% CI 0.99 to 1.65) [18]. The meta-analysis rated its mortality evidence low quality [23].
LimitedHow often is not known

Tooth enamel erosion from chewable vitamin C

Case reports: daily chewing of vitamin C tablets eroded tooth enamel. Lab tests found chewable vitamin C tablets acidic enough to wear enamel.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
A patient had severe dental erosion attributed mainly to chewing vitamin C tablets daily for 3 years. A solution made from one tablet demineralized enamel in testing [25]. A second case report describes localized enamel erosion from excess chewable vitamin C [26]. In a laboratory study, six children's chewable vitamin tablets had a pH of 2.99 to 4.77, and the vitamin C tablets caused more enamel weight loss than the multivitamins over 14 days [27].
Population
Case reports [25][26]; human enamel samples in vitro [27].
Sources
[25], [26], [27]
Caveats
Case reports and laboratory tests give no rate in people. This concerns tablets held or chewed in the mouth, not vitamin C in general.

Checked, no increase found1

Moderate

Mortality

Deaths were about as common as on placebo across 29 low-bias trials of adults.

The numbers and sources
How common
Common: between 1 in 100 and 1 in 10 people.
Effect
In trials with low risk of bias, vitamin C did not change mortality (9.9% against 9.3%, RR 1.02, 95% CI 0.98 to 1.07, 29 trials) [24].
Population
Adults in primary and secondary prevention trials [24].
Sources
[24]
Caveats
Antioxidants in these trials were given alone or in combination with other vitamins, minerals or interventions [24].

Claims tested and not found

  1. That vitamin C keeps most people from catching colds. In community trials the risk did not change (RR 0.97) [1].
  2. That vitamin C taken at the first sign of a cold shortens it. Therapeutic trials showed no consistent effect [1].
  3. That vitamin C prevents heart disease or cancer. In 14,641 men followed 8 years, neither differed from placebo [10][11].
  4. That vitamin C lowers death from COVID-19. A meta-analysis of 9 randomized trials and a second of 13 studies found no change in mortality [3][4].
  5. That vitamin C added to periodontal treatment reduces gum pocket depth. Probing depth and attachment did not improve significantly at 3 months across 6 RCTs [8].

Sources

  1. Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews. 2013. https://doi.org/10.1002/14651858.CD000980.pub4
  2. Juraschek SP, Guallar E, Appel LJ, et al. Effects of vitamin C supplementation on blood pressure: a meta-analysis of randomized controlled trials. The American Journal of Clinical Nutrition. 2012. https://doi.org/10.3945/ajcn.111.027995
  3. Abid H, Mushtaq I, Munir ABI, et al. Vitamin C for the management of COVID-19: a systematic review and meta-analysis of randomized controlled trials. Annals of Medicine & Surgery. 2026. https://doi.org/10.1097/MS9.0000000000004838
  4. Zhou S, Gao S, Fang Y, et al. Efficacy of vitamin C in COVID-19 management: a systematic review and meta-analysis. BMC Infectious Diseases. 2025. https://doi.org/10.1186/s12879-025-11891-6
  5. Qin M, Xu K, Chen Z, et al. Effects of Vitamin C Supplements on Clinical Outcomes and Hospitalization Duration for Patients with Coronavirus Disease 2019 (COVID-19): A Systematic Review and Meta-Analysis. Nutrition Reviews. 2025. https://doi.org/10.1093/nutrit/nuae154
  6. Qu J, Yao M, Yu S, et al. Overall and Progression-Free Survival of Patients With Malignant Neoplasm Following Intravenous Vitamin C: A Systematic Review and Meta-Analysis. International Journal for Vitamin and Nutrition Research. 2025. https://doi.org/10.31083/IJVNR37372
  7. Hujoel PP, Kato T, Hujoel IA, Hujoel MLA. Bleeding tendency and ascorbic acid requirements: systematic review and meta-analysis of clinical trials. Nutrition Reviews. 2021. https://doi.org/10.1093/nutrit/nuaa115
  8. Fageeh HN, Fageeh HI, Prabhu A, et al. Efficacy of vitamin C supplementation as an adjunct in the non-surgical management of periodontitis: a systematic review. Systematic Reviews. 2021. https://doi.org/10.1186/s13643-020-01554-9
  9. Ul Hassan A, Hanif A, Hassan M, et al. Effectiveness of vitamin C and D supplementation as an adjunct in the management of gingivitis in school-going children: a randomized controlled trial. BMC Public Health. 2026. https://doi.org/10.1186/s12889-026-27539-2
  10. Sesso HD, Buring JE, Christen WG, et al. Vitamins E and C in the Prevention of Cardiovascular Disease in Men. JAMA. 2008. https://doi.org/10.1001/jama.2008.600
  11. Gaziano JM, Glynn RJ, Christen WG, et al. Vitamins E and C in the Prevention of Prostate and Total Cancer in Men. JAMA. 2009. https://doi.org/10.1001/jama.2008.862
  12. Ranchordas MK, Rogerson D, Soltani H, et al. Antioxidants for preventing and reducing muscle soreness after exercise. Cochrane Database of Systematic Reviews. 2017. https://doi.org/10.1002/14651858.CD009789.pub2
  13. Paulsen G, Cumming KT, Holden G, et al. Vitamin C and E supplementation hampers cellular adaptation to endurance training in humans: a double-blind, randomised, controlled trial. The Journal of Physiology. 2014. https://doi.org/10.1113/jphysiol.2013.267419
  14. Eberlein-König B, Placzek M, Przybilla B. Protective effect against sunburn of combined systemic ascorbic acid (vitamin C) and d-alpha-tocopherol (vitamin E). Journal of the American Academy of Dermatology. 1998. https://doi.org/10.1016/s0190-9622(98)70537-7
  15. McArdle F, Rhodes LE, Parslew R, et al. UVR-induced oxidative stress in human skin in vivo: effects of oral vitamin C supplementation. Free Radical Biology and Medicine. 2002. https://doi.org/10.1016/s0891-5849(02)01042-0
  16. Natarelli N, Aflatooni S, Stankiewicz K, et al. Oral Supplements and Photoprotection: A Systematic Review. Journal of Medicinal Food. 2025. https://pubmed.ncbi.nlm.nih.gov/39804624/
  17. Lamontagne F, Masse MH, Menard J, et al. Intravenous Vitamin C in Adults with Sepsis in the Intensive Care Unit. New England Journal of Medicine. 2022. https://doi.org/10.1056/NEJMoa2200644
  18. Stoppe C, Hill A, Cancio LC, et al. High-Dose Intravenous Vitamin C and Mortality and Organ Dysfunction in Severe Burn Injury: The VICTORY Randomized Clinical Trial. JAMA. 2026. https://doi.org/10.1001/jama.2026.10616
  19. Rozemeijer S, Dubois EA, de Grooth HJ, et al. Early high-dose vitamin C for out-of-hospital cardiac arrest: the VITaCCA randomized clinical trial. Intensive Care Medicine. 2026. https://doi.org/10.1007/s00134-026-08492-5
  20. European Food Safety Authority. Overview on Tolerable Upper Intake Levels as derived by the Scientific Committee on Food (SCF) and the EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Version 11. 2025. https://www.efsa.europa.eu/sites/default/files/assets/UL_Summary_tables.pdf
  21. Ferraro PM, Curhan GC, Gambaro G, et al. Total, Dietary, and Supplemental Vitamin C Intake and Risk of Incident Kidney Stones. American Journal of Kidney Diseases. 2016. https://doi.org/10.1053/j.ajkd.2015.09.005
  22. Farkouh A, Seibly E, Buell MI, et al. The Effect of Vitamin C Supplements on Urinary Stone Risk: A Systematic Review and Meta-Analysis. Journal of Endourology. 2026. https://doi.org/10.1177/08927790261471733
  23. Cai B, Xiao Q, Xia Y, et al. Intravenous vitamin C as micronutrient therapy in patients with sepsis or septic shock: an updated systematic review and meta-analysis of randomized controlled trials. Frontiers in Nutrition. 2026. https://doi.org/10.3389/fnut.2026.1905726
  24. Bjelakovic G, Nikolova D, Gluud LL, et al. Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database of Systematic Reviews. 2012. https://doi.org/10.1002/14651858.CD007176.pub2
  25. Giunta JL. Dental erosion resulting from chewable vitamin C tablets. Journal of the American Dental Association. 1983. https://doi.org/10.14219/jada.archive.1983.0239
  26. Bahal P, Djemal S. Dental erosion from an excess of vitamin C. Case Reports in Dentistry. 2014. https://doi.org/10.1155/2014/485387
  27. Lertsooksawat W, Tanjaruphan Y, Chaima T, et al. Erosive potential of children's chewable vitamin supplements: An in vitro investigation. Journal of Dental Research, Dental Clinics, Dental Prospects. 2024. https://doi.org/10.34172/joddd.41791
  28. Cosgrove MC, Franco OH, Granger SP, et al. Dietary nutrient intakes and skin-aging appearance among middle-aged American women. The American Journal of Clinical Nutrition. 2007. https://doi.org/10.1093/ajcn/86.4.1225

Everything in the library