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Vitamin C and COVID-19 Research Resource

This online resource is an up-to-date repository of published and ongoing vitamin C and COVID-19 research studies and related resources. Contact: Associate Professor Anitra Carr ( if you wish to provide relevant resources or receive further information.
Page last updated: 20 July 2021

In March 2020, the World Health Organization (WHO) published a ‘Coordinated Global Research Roadmap for the 2019 Novel Coronavirus’. In this document vitamin C was highlighted as an adjunctive intervention with biological plausibility to improve the outcome of COVID-19 infected patients (pages 36-7).

Vitamin C and COVID-19 observational studies

Low vitamin C levels can predispose people to viral infections. In addition, viral infections can further decrease vitamin C levels due to enhanced requirements for the vitamin during infections. Below is a summary of COVID-19 and vitamin C observational studies which indicate that patients with COVID-19 have depleted vitamin C status. Definitions: vitamin C deficiency ≤11 µmol/L (<0.2 mg/dL); hypovitaminosis C ≤23 µmol/L (<0.4 mg/dL).

Observational study summaries

Study 1 Vitamin C levels in patients with SARS-CoV-2-associated acute respiratory distress syndrome
Date online 26 August 2020
Location Barcelona Spain
Cohort 18 patients with SARS-CoV-2-associated acute respiratory distress syndrome (ARDS)
Findings 17 patients had <1.5 mg/L (<8.5 µmol/L) vitamin C
1 patient had 2.4 mg/L (14 µmol/L) vitamin C
Reference Chiscano-Camón et al. Crit Care. 2020 24(1):522. doi:10.1186/s13054-020-03249-y

Study 2 Serum levels of vitamin C and vitamin D in a cohort of critically Ill COVID-19 patients of a North American community hospital intensive care unit in May 2020: A pilot study
Date online 18 September 2020
Location Thornton, Colorado, USA
Cohort 21 critically ill COVID-19 patients
Findings Plasma Vitamin C graphTotal cohort (n = 21) mean vitamin C status 22 ± 4 µmol/L (45% deficient, 70% hypovitC)
Survivors (n = 11) mean vitamin C status 29 ± 7 µmol/L (40% deficient, 50% hypovitC)
Non-survivors (n = 10) mean vitamin C status 15 ± 2 µmol/L (50% deficient, 90% hypovitC)
Reference Arvinte et al. Med Drug Discov. 2020 8:100064. doi:10.1016/j.medidd.2020.100064

Study 3 Vitamin C supplementation is necessary for patients with coronavirusdisease: An ultra-high-performance liquid chromatography-tandemmass spectrometry findingYaru
Date online 27 January 2021
Location Shanghai, China
Cohort 31 COVID-19 patients (+/- IV vitamin C) and 51 healthy controls
Findings Plasma Vitamin C graph.6 COVID-19 patients (no IV vitamin C): mean plasma vitamin C level 2 mg/dl (11 µmol/L)
25 COVID-19 patients given 100 mg/kg/d IV vitamin C: mean plasma vitamin C level 13.5 mg/L (76 µmol/L)
51 healthy controls: mean plasma vitamin C level 9.2 mg/L (52 µmol/L)
Reference Xing et al. J Pharm Biomed Anal. 2021, 196:113927. doi: 10.1016/j.jpba.2021.113927

Study 4COVID‑19: Up to 82% critically ill patients had low Vitamin C values
Date online9 July 2021
LocationBarcelona, Spain
Cohort67 critically ill COVID-19 patients with acute respiratory distress syndrome (ARDS)
FindingsMean vitamin C concentration was 8 ± 3 µmol/L (0.14 ± 0.05 mg/dL);
range of <6 – 61 µmol/L (<0.10 – 1.08 mg/dL)
55 patients (82%) had values <23 µmol/L (<0.40 mg/dL)
12 patients (18%) had values <6 µmol/L (<0.10 mg/dL)
ReferenceTomasa‑Irriguible and Bielsa‑Berrocal. Nutr Res. 2021 20(1):66. doi: 10.1186/s12937-021-00727-z.

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Vitamin C and COVID-19 intervention trials

Randomised controlled trials (RCTs) of patients with respiratory infections, pneumonia and sepsis have indicated that vitamin C administration may be able to improve some patient outcomes. Critically ill patients with sepsis require intravenous administration of gram doses of vitamin C to normalise their plasma vitamin C levels. Below is a summary of vitamin C and COVID-19 intervention trials which indicate that some symptoms of COVID-19 patients may be improved with vitamin C administration.

Intravenous vitamin C - randomised controlled trials

RCT 1 Pilot trial of high-dose vitamin C in critically ill COVID-19 patients
Date online 9 August 2020
Location Hubei, China (multicentre)
Trial type Randomised placebo-controlled trial
Cohort 54 critically ill COVID-19 patients (27 and 29 per group)
Intervention 24 g/day IV vitamin C (12 g/12 hours) for 7 days (or placebo)
Findings Fig 3 thumbno difference in ventilation-free days (26.5 vs 10.5 days, p = 0.560)
↑ PaO2/FiO2 (229 vs 151 mmHg, p = 0.01)
↓ Interleukin-6 (19.4 vs 158 pg/ml, p = 0.04)
↓ ICU and hospital mortality in patients with SOFA scores ≥3 (4 vs 10 days, p = 0.03)
Notes Trial was stopped early due to lack of patients
Reference Zhang et al. Ann Intensive Care, 2021, 11, 5

RCT 2 The role of vitamin C as adjuvant therapy in COVID-19
Date online 30 November 2020
Location Karachi, Pakistan
Trial type Randomised controlled trial (open label)
Cohort 150 severe COVID-19 patients (75 per group)
Intervention 50 mg/kg bodyweight/day IV vitamin C (or standard therapy alone)

Fig 4 thumbBecame symptom-free earlier (7.1 vs 9.6 days, p <0.0001)
Spent fewer days in the hospital (8.1 vs 10.7 days, p <0.0001)
No difference regarding need for mechanical ventilation (16% vs 20%, p = 0.4)
No difference regarding mortality (9.3% vs 14.6%, p = 0.3)

Reference Kumari et al. Cureus 2020 12(11): e11779. doi:10.7759/cureus.11779

RCT 3 Safety and effectiveness of high‑dose vitamin C in patients with COVID‑19: a randomized open‑label clinical trial
Date online 11 February 2021
Location Tehran, Iran
Trial type Randomised controlled trial (open-label)
Cohort 60 patients with COVID-19 (30 per group)
Intervention 6 g/d IV vitamin C (or standard care) for 5 days
Findings ↓ body temperature on 3rd day of hospitalization (p = 0.001)
↑ peripheral capillary oxygen saturations (SpO2) on 3rd day of hospitalization (p = 0.014)
Comparable SpO2 levels (oxygen saturation) at discharge
↑ length of hospitalization (8.5 days vs. 6.5 days, p = 0.028).
No difference in length of intensive care unit (ICU) stay or mortality
No adverse events were reported
Reference JamaliMoghadamSiahkali et al. Eur J Med Res. 2021, 26(1):20. doi: 10.1186/s40001-021-00490-1

Intravenous vitamin C - retrospective cohort studies

Study 1 The efficiency and safety of high-dose vitamin C in patients with COVID-19: a retrospective cohort study
Date online 26 February 2021
Location Xi'an, Shaanxi, China
Trial type Retrospective cohort
Cohort 76 patients with COVID-19
Intervention Loading dose of 6 g intravenous infusion per 12 hr on the first day, and 6 g once for the following 4 days (n=46)
or standard therapy group (n=30)
Findings Fig 6 thumbRisk of 28-day mortality was reduced (HR=0.14, 95% CI, 0.03-0.72)
Oxygen support status was improved compared with standard therapy (64% vs 36%)
No adverse safety events were associated with high-dose vitamin C therapy
Notes Fig 7 thumbMortality differences were even more pronounced for (A) those with severe COVID-19 (HR= 9.91, 95% CI, 1.82-54.00) and (B) those aged >60 years (HR=7.98, 95% CI, 1.24-51.22).

Fig 8 thumb

Reference Gao et al. Aging. 2021:13. doi: 10.18632/aging.202557.
Study 2 High Dose Intravenous Vitamin C for Preventing The Disease Aggravation of Moderate COVID-19 Pneumonia. A Retrospective Propensity Matched Before-After Study
Date online 22 April 2021
Location Shanghai, China
Trial type Retrospective propensity matched
Cohort 110 patients with moderate COVID-19 pneumonia (55 per group)
Intervention 100 mg/kg/day IV vitamin C for 7 days vs standard care
Findings ↓ number of patients progressing to severe type (4/55 vs 12/55; RR 0.28 [0.08, 0.93], P = 0.03)
↓ duration (P < 0.001) and ↓ incidence (2/21 vs 10/22, P = 0.08) of systemic inflammation (SIRS)
↓ C-reactive protein levels (P = 0.05), ↓ activated partial thromboplastin (blood clotting) time (P = 0.02), ↑ CD4+ (helper) T cells (P = 0.04)
No Effect on time to negative nucleic acid load
Reference Zhao et al. Frontiers Pharmacol, 2021, 12:638556.
Study 3 Effect of high-dose intravenous vitamin C on prognosis in patients with SARS-CoV-2 pneumonia
Date online 11 May 2021
Location Ankara, Turkey
Trial type Retrospective 
Cohort 232 patients with severe acute respiratory syndrome due to COVID-19 infection
Intervention 2 g/day IV vitamin C initiated within a median duration of 3 days after admission (n=153)
vs no vitamin C (n=170)
Findings Those in the VC group were not significantly different in terms of the length of hospital stay (p=0.05), re-admission rate (p=0.943), admission to intensive care, need for advanced oxygen support (p=0.488), need for advanced medical treatment (p<0.001), and mortality (p=0.52)
No adverse effects associated with the use of IV vitamin C treatment were recorded.
Reference Suna et al. Med Clin (Barc). 2021;S0025-7753(21)00252-9. doi: 10.1016/j.medcli.2021.04.010.
Study 4 Use of Intravenous Vitamin C in Critically Ill Patients With COVID-19 Infection
Date online 8 June 2021
Location New York, United States of America
Trial type Retrospective observational cohort study with propensity score matching
Cohort ICU patients with COVID-19 infection
Intervention 1.5 grams IV vitamin C every 6 hours for up to 4 days (n = 8) vs matched patients (n = 24)
Findings Patients in the IV vitamin C group had higher rates of hospital mortality [7 (88%) vs. 19 (79%), P = 0.049] and mean SOFA scores post-treatment (12.4 ± 2.8 vs. 8.1 ± 3.5, P < 0.005).
There was no difference in the daily vasopressor requirement or in ICU length of stay between the treatment and control groups.
Reference Li et al. J Pharm Pract. 2021;8971900211015052. doi: 10.1177/08971900211015052.

Oral vitamin C - randomised controlled trials

RCT 1 Effect of High-Dose Zinc and Ascorbic Acid Supplementation vs Usual Care on Symptom Length and Reduction Among Ambulatory Patients With SARS-CoV-2 Infection: The COVID A to Z Randomized Clinical Trial
Date online 12 February 2021
Location Ohio and Florida, USA
Trial type Randomised controlled trial (open-label)
Cohort 214 patients with SARS-CoV-2 infection (48 - 58 per group)
Intervention 8 g/d oral vitamin C
or 50 mg/d zinc gluconate
or both vitamin C and zinc gluconate
or standard care for 10 days
Findings Non-significant decrease in number of days to reach 50% reduction in symptoms of approx. one day for treatment groups compared with standard care:
Standard care group 6.7 (± 4.4) days
Vitamin C group 5.5 (± 3.7) days
Zinc gluconate group 5.9 (± 4.9) days
Both vitamin C and zinc gluconate group 5.5 (± 3.4) days
Notes Fig 5 thumbTrial was stopped early as interventions assumed to be ineffective (although the difference between the vitamin C and standard care groups was greater than originally anticipated by the authors).
Independent statistical analysis of the data has indicated that vitamin C increased the rate of recovery by 71% (P = 0.036)
Reference Thomas et al. JAMA Network Open 2021 4(2):e210369. doi:10.1001/jamanetworkopen.2021.0369
RCT 2 The effect of vitamin E and vitamin C in patients with COVID-19 pneumonia; a randomized controlled clinical trial
Date online 14 April 2021
Location Isfahan, Iran
Trial type Randomised controlled trial 
Cohort 72 non-serious hospitalized COVID-19 patients
Intervention 1000 mg oral vitamin (plus 400 IU vitamin E) daily (n=38) administered until hospital discharge or ICU admission vs standard care (n=34)
Findings No difference in clinical improvement or duration of hospitalisation.
No patients died in the study.
Reference Hakamifard et al. Immunopathol Persa. 2021;7(2):exx

Oral vitamin C - case control studies

Study 1Role of ivermectin in the prevention of SARS-CoV-2 infection among healthcare workers in India: A matched case-control study
Date online16 February 2021
LocationBhubaneswar, India
Study typeCase control
Cohort372 health-care workers who tested positive (cases) or negative (controls)
Intervention67 took prophylactic vitamin C at 500 mg/day (or twice daily) vs 305 who did not
FindingsVitamin C prophylaxis was not associated with SARS-CoV-2 infection (OR 0.71, 95% CI, 0.40–1.26)
ReferenceBehera et al. PLoS ONE 16(2): e0247163.

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Registered vitamin C and COVID-19 clinical trials

Registered vitamin C and COVID-19 clinical trials can be found at

Some of these trials are testing vitamin C as a prophylactic (preventative), while others are testing it as an adjunctive therapy/treatment (i.e. in addition to standard care). Some of these trials are using vitamin C alone (monotherapy), while others are using combination therapies. Some are using oral vitamin C and others intravenous vitamin C administration (summarised in Carr and Rowe, Nutrients, 2020. doi: 10.3390/nu12113286)

Largest vitamin C and COVID-19 trials

Published study protocols

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Vitamin C and COVID-19 in clinical practice

Many clinicians and clinical teams worldwide are administering vitamin C to their COVID-19 patients. Some protocols use vitamin C monotherapy in addition to standard care, others as part of combination therapies, for both prophylaxis and treatment.

Clinical protocols

Vitamin C and COVID-19 in case reports

Case reports do not have untreated patients as comparators so cannot provide definitive evidence that vitamin C is exerting any additional benefit over standard therapy alone.

Case reports with positive outcomes

Case reports with negative outcomes

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Evidence for mechanisms of action

Many mechanisms of action have been proposed for vitamin C against SARS-CoV-2 and COVID-19, based on previous research with similar viruses and respiratory infections, e.g. anti-viral, anti-inflammatory, anti-oxidant, and immunomodulatory. Below are in vitro (laboratory-based) and in vivo (clinical) studies that have been carried out with SARS-CoV-2 and COVID-19 patients.

In vitro (laboratory-based) studies

In vivo (clinical) studies

Intravenous vitamin C administration to COVID-patients:

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Vitamin C and COVID-19 review articles

Many review articles and commentaries have been written about vitamin C and COVID-19. Published articles that have specifically focused on vitamin C are shown below.

Published review articles

Published commentaries


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Vitamin C and COVID-19 in the media

There are many articles in the global media regarding vitamin C and COVID-19. Some of the posts directly related to this topic are shown below.

Clinical studies in the media

Clinical practice in the media

Case reports in the media

Reviews/overviews in the media


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Contact Associate Professor Anitra Carr if you wish to provide relevant resources of receive further information.

Tel: +64 3 364 0649

How to cite this resource

Carr, A.C. Vitamin C and COVID-19 Research Resource,