The Impact of Vitamin D Level on COVID-19 Infection: Systematic Review and Meta-Analysis

This meta-analysis suggests that sufficient vitamin D level in serum is associated with a significantly decreased risk of COVID-19 infection. Clinical trials are needed to establish if supplementation is warranted.

To summarize available literature regarding the impact of vitamin D level on COVID-19 infection.

• The summary of results indicated that being vitamin D deficient wincreased the risk of COVID-19 infection as compared to vitamin D sufficient. This review has shown that when there is lower serum 25(OH) D level, the risk or susceptibility to COVID-19 increases.
• Eight of the 14 selected studies reported the impact of vitamin D level on COVID-19 infection. Overall, pooled OR in the random-effect model showed that VDD was associated with an increased risk of COVID-19 infection (OR = 1.80, 95% CI: 1.72, 1.88).
• Those individuals with an insufficient level of Vitamin D are 80% more likely to acquire COVID-19 infection as compared to those who have a normal level of Vitamin D.

Fourteen studies with data for 91,120 participants. Three studies were performed Europe, two in America, two in Asia. They included a mix of study designs including cohort, case control, cross sectional and 1 interim audit.

• It is important to consider that the studies included are limited to the inclusion/exclusion criteria of the study design and, therefore, may miss important studies with slightly different design, but meaningful data.
• In addition, in order to conduct a meta-analysis the studies included must have similar endpoints to extract and, in doing so, researchers may group together studies that are not the same, but will be analyzed as the same which can lead to skewed conclusions.
• A meta-analysis only includes studies that have been published and, therefore, information gathered may be subject to publication bias. This means that studies that show no effect or the opposite of the expected effect may not be published and, therefore, not included.
• In this review, most of the included studies were hospital-based studies and the data were from secondary sources that become more prone to high risk of bias.

In conclusion, low serum 25 (OH) Vitamin-D level was significantly associated with a higher risk of COVID-19 infection. The limited currently available data suggest that sufficient Vitamin D level in serum is associated with a significantly decreased risk of COVID-19 infection.

• This was a systematic review and meta-analysis which followed the established Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA)Guidelines.
• Before starting the literature review, search methods as well as criteria for which studies to include and exclude were established.
• The authors conducted a systematic search of databases (PubMed/Medline, Cochrane/Wiley library, Scopus, and SciELO) from May 15, 2020, to December 20, 2020, using key terms. In addition, reference lists of relevant studies were identified. The search strategy was built using a combination of keywords for the main axes of the research questions. The search strategy used terms related to (a) COVID-19/SARS-CoV-2 and (b) vitamin D level/supplement.
• Data extracted included characteristics of the study population, sample size, participant’s status, and level of vitamin D, and outcomes of the study. The reported odds ratio (OR) or Risk ratio (RR) and the corresponding 95% CI or other relevant data were extracted.
• VDD and insufficiency was defined as a 25(OH) D level of <20 ng/mL (50 nmol/L) or as a 25(OH) D of 21–29 ng/ml (52.5–72.5 nmol/L), respectively, and sufficient/normal if 25(OH)D level was ≥30 ng/ml.
• The methodological quality of the studies was evaluated by two reviewers (AT and ZA) using JBI tools.

Teshome A, Adane A, Girma B, Mekonnen ZA. The Impact of Vitamin D Level on COVID-19 Infection: Systematic Review and Meta-Analysis. Front Public Health. 2021 Mar 5;9:624559. doi: 10.3389/fpubh.2021.624559. PMID: 33748066; PMCID: PMC7973108.