eng Enviro Research Publishers Current Research in Nutrition and Food Science Journal 2347-467X 2322-0007 2023-04-25 11 1 37 60 10.12944/CRNFSJ.11.1.3 15985 article Moamen Mostafa Asla 1 Asmaa Ahmed Nawar 1 Samar A. Amer 1 Esraa Elsayed 4 Ramadan Abdelmoez Farahat 5 Ayah Abdulgadir 6 Faculty of Human Medicine, Zagazig University, Zagazig City, Sharkia, Egypt Department of Public Health and Community Medicine, Faculty of Medicine, Zagazig University, Zagazig City, Sharkia, Egypt Membership at the Royal Colleague of General Practitioners[INT], London, United Kingdom Department of Mental Health Primary Care, Nova University, Lisbon Faculty of Medicine, Kafrelsheikh University, Kafrelsheikh, Egypt Faculty of Medicine, University of Khartoum, Sudan Numerous connections between the level of vitamin D (Vit-D) and the novel coronavirus disease -19 (COVID-19) have surfaced during the pandemic. So, we conducted this systematic review and meta-analysis to explore the effect of Vit-D deficiency and its supplementation on the clinical outcomes of COVID-19 patients. We looked for relevant articles in Cochrane Library, Scopus, Web Science, PubMed, and EBSCO up until the end of 2022. The Open Meta Analyst software was used to analyze the extracted data. We classified them into two main categories based on their objectives. First, the studies that evaluated the effects of Vit-D deficiency in patients, and lastly, the studies that evaluated Vit-D as a supplement, both on mortality rate, hospitalization duration, ICU admission rate, and mechanical ventilation rate. A total of 8001 COVID-19 patients from 42 studies were included. A high serum Vit-D concentration compared to those with lower levels was associated with a significantly lower mortality rate (RR = 1.5, 95% CI = 1.11: 2.02, p = 0.01). According to the estimated effect of 18 studies, those who took Vit-D supplements had a significantly lower mortality rate, hospitalization duration, ICU admission rate, and mechanical ventilation rate than those who did not. The group receiving Vit-D doses between 50 000 to 100 000 IU had a significantly better clinical outcome compared to lower and higher doses. COVID-19 patients with normal Vit-D levels had significantly lower death rates than those with hypovitaminosis. Vit-D supplements in COVID-19 significantly improved clinical outcomes. Vit-D supplementation between 50 000 to 100 000 IU, in patients with COVID-19 significantly outperformed other doses in terms of mortality. https://www.foodandnutritionjournal.org/volume11number1/vitamin-d-on-covid-19-patients-during-the-pandemic-2022-a-systematic-review-and-meta-analysis/ Clinical Outcome Efficacy Vitamin D deficiency Vitamin D supplements SARS-CoV-2 virus