Question & Answer

Can taking large doses of Vitamin C help to prevent COVID-19?

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  • There have been claims suggesting that Vitamin C can be used as a treatment for COVID-19. Some claims have also recommended taking large doses of Vitamin C to prevent COVID-19.
  • Vitamin C (ascorbic acid) is an essential vitamin. Adults need about 45mg of Vitamin C a day, and you can get it by eating fruit and vegetables. If you don’t get enough Vitamin C for several months, it can cause a disease called scurvy.
  • Using Vitamin C to help prevent and treat colds and flu has long been controversial. Although Vitamin C supports the immune system (European Food Safety Authority), there’s little evidence that it can prevent or treat colds, let alone COVID-19, which is a more serious disease and potentially more harmful.
  • Sales of dietary supplements such as Vitamin C increased during the pandemic, with many people believing they have “immune-boosting”
  • One study report suggested that higher levels of dietary intake of Vitamin C reduced the risk of developing COVID-19 after contact with an infected person. However, this study depended on participants reporting their diets themselves, which may not be reliable.
  • Evidence regarding the use of Vitamin C to prevent COVID-19 is lacking.

Things to Remember


  • Lead Researcher: Dr. Caoimhe Madden, Postdoctoral researcher, Evidence Synthesis Ireland, School of Nursing and Midwifery, University of Galway
  • Reviewed by: Prof Declan Devane, Professor of Health Research Methodology, Deputy Dean, College of Medicine, Nursing and Health Sciences, University of Galway, Scientific Director, HRB-Trials Methodology Research Network Director, Evidence Synthesis Ireland. Director, Cochrane Ireland
  • Topic advisor: Dr. Frank Moriarty,  Pharmacist and lecturer at the School of Pharmacy and Biomolecular Sciences, Royal College of Surgeons in Ireland and visiting research fellow at The Irish Longitudinal Study on Ageing (TILDA)   
  • Public and Patient advisor: Anne Daly, Public and Patient Involvement in research (PPI) advisor, PPI Ignite, NUI Galway
  • Journalist Advisor: Claire O’Connell, PhD in cell biology, MSc Communication. Contributor to The Irish Times, writing about health, science and innovation.

Conflict of Interest Statement: The authors have no financial or other conflicts of interest for this health claim summary.