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This online resource is an up-to-date repository of published and ongoing vitamin C and COVID-19 research studies and related resources.

If you wish to provide relevant resources or receive further information, contact:

Research Professor Anitra Carr
Email anitra.carr@otago.ac.nz

Page last updated: 13 May 2024

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 studies

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 (RCTs)

Intravenous vitamin C administration provides higher blood concentrations of the vitamin than oral supplementation. RCTs are considered the gold standard design for drug trials, however, for nutrient trials there is never a true control group as the nutrient (vitamin C) is generally being obtained through dietary intake, including in the control group.

Intravenous vitamin C – retrospective cohort studies

Retrospective cohort studies are not as robust as RCTs as the two study groups are retrospectively (historically) identified and then compared, e.g. those who received vitamin C versus those who didn’t. These studies can be prone to various underlying biases.

Oral vitamin C – randomised controlled trials

Oral vitamin C supplementation does not provide as high blood concentrations as intravenous vitamin C. Also note issues with nutrient RCTs outlined above.

Oral vitamin C – retrospective cohort studies

Note issues discussed above regarding oral versus intravenous vitamin C and retrospective cohort versus RCT study design.

Vitamin C intake or status and COVID-19 risk

These are observational studies only so cannot confirm cause and effect relationships as the studies are prone to various confounding factors. There are also issues with Mendelian randomization studies as outlined in commentary below.

Registered vitamin C and COVID-19 clinical trials

Registered vitamin C and COVID-19 clinical trials can be found at clinicaltrials.gov and the International Clinical Trials Registry Platform. 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.

Published study protocols

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

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:

Meta-analyses and 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. Meta-analyses, which combine the outcomes from multiple studies, are now also becoming available.

Published meta-analyses

Published review articles

Published commentaries

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

Podcasts/videos

Feedback

“A useful repository of studies on vitamin C and COVID‑19 is managed by Professor Anita Carr at the University of Otago who has herself has contributed much to research with Vitamin C and both communicable and non-communicable disease.”

Prof R Mithen, Chief Scientist, NZ High Value Nutrition National Science Challenge.

“I live in Canada and I was exposed to COVID‑19 in late December, and fell seriously ill [positive COVID test]. Everyone has a different experience with the virus but what stuck out to me was my constant craving for orange juice, I drank gallons of it, which I usually don't drink. The sickness passed and I stopped craving it. I really think there is something to these studies.”

B Okojie, Canada.

“I feedback quite a lot of information to our Access and Choice practitioners who are seeing a lot of people in primary care with health anxiety. I have highlighted your page to help explain why there is evidence of the use of vitamin C in the treatment of COVID but not as a preventative in place of vaccination.”

H Gibbs, Nutrition Development Advisor, WellSouth Primary Health Network, NZ

Contact

Please contact Professor Anitra Carr if you wish to highlight relevant resources or receive further information.

Email anitra.carr@otago.ac.nz
Tel +64 3 364 0649

How to cite this resource

Carr, A.C. Vitamin C and COVID-19 Research Resource,
otago.ac.nz/christchurch/research/nutrition-in-medicine/vitamin-c

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