Vitamin C and D supplementation and the severity of COVID-19: A protocol for systematic review and meta-analysis

Medicine (Baltimore). 2021 Jul 2;100(26):e26427. doi: 10.1097/MD.0000000000026427.


Background: The COVID-19 pandemic has rapidly spread to other countries, causing numerous deaths and challenges for organizations and health professionals. Diet and nutrition invariably influence the competence of the immune system and determine the risk and severity of infections. Studies have already been published on the relationships through which vitamins C and D can mitigate the severity of infections such as COVID-19. In this context, this protocol describes a systematic review intended to analyze if vitamin C and D supplementation can reduce the severity of Covid-19.

Methods: This protocol was developed based on the recommendations of PRISMA-P. In order to accomplish the systematic review, we will carry out searches in the PubMed, Web of Science, Scopus, Cochrane, and ScienceDirect databases in the quest for control case studies that analyze the supplementation and evolution of patients with COVID-19. There will be no limitations related to language or publication time. The searches will be carried out by 2 independent researchers who will select the articles, and then the duplicate studies will be removed, while the suitable ones will be selected using the Rayyan QCRI application. In order to assess the risk of bias, we will use the instrument proposed by the National Heart, Lung and Blood Institute. Moreover, we will carry out metaanalyses and subgroup analyses according to the conditions of the included data.

Results: This review will assess the association between vitamin C and D supplementation and the reduction in the severity of COVID-19.

Conclusion: The findings of this systematic review will summarize the latest evidence for the association between vitamin C and D supplementation and COVID-19 through a systematic review and meta-analysis.

Record of systematic review: CRD42021255763.

MeSH terms

  • Ascorbic Acid / administration & dosage*
  • COVID-19 / diagnosis*
  • Dietary Supplements*
  • Humans
  • Meta-Analysis as Topic*
  • Nutritional Status
  • Pandemics
  • SARS-CoV-2
  • Severity of Illness Index*
  • Systematic Reviews as Topic*
  • Vitamin D / administration & dosage*


  • Vitamin D
  • Ascorbic Acid