Low vitamin D status is associated with coronavirus disease 2019 outcomes: a systematic review and meta-analysis.

Vitamin D deficiency and obesity increases risk of testing positive for COVID-19.

To assess the association between low vitamin D status and COVID-19.

• The pooled OR in a fixed-effect model showed that vitamin D deficiency or insufficiency was associated with an increased risk of COVID-19 infection (OR = 1.43, 95% CI 1.00–2.05). However, high heterogeneity was observed in the studies (I2 = 64.9%, p = 0.036).
• The average vitamin D level of the COVID-19-positive group was lower than the COVID-19-negative group

A total of ten articles with 361,934 participants were selected for meta-analysis.

• 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 This means that studies that show no effect or the opposite of the expected effect may not be published and therefore not included.
• Correlation does not equal causation, and whether low vitamin D levels are a cause or consequence of COVID-19 remains uncertain.
• There are discrepancies in the number and sample size of the included studies, leading to some large variances in effect size estimates.
• Significant heterogeneity was found.

This systematic review and meta-analysis indicated that low vitamin D status might be associated with an increased risk of COVID-19 infection. Further studies are needed to evaluate the impact of vitamin D supplementation on the clinical severity and prognosis in patients with COVID-19.

• 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.
• A systematic search was conducted by 2 authors with PubMed, Embase, and the Cochrane Library from database inception to September 25, 2020.
• The following search terms were entered: (“coronavirus disease 2019″ OR “COVID-19″ OR “SARS−COV-2″ OR “Coronavirus”) AND (“vitamin D” OR “25(OH)D” OR “25-hydroxyvitamin D” OR “hydroxycholecalciferols” OR “hypovitaminosis D”).
• The population (P) included individuals with COVID-19 who had low vitamin D status, including vitamin D deficiency or insufficiency, (E), and were compared (C) to individuals without COVID-19. The primary outcome (O) was incident COVID-19.
• Observational studies (S) were included in this meta-analysis.
• Vitamin D deficiency or insufficiency is defined as a 25(OH)D below 20 ng/mL (50 nmol/L) or as a 25(OH)D of 21–29 ng/ml (52.5–72.5 nmol/L), respectively.
• Bias was assessed by the modified Newcastle-Ottawa scale (NOS).

Liu N, Sun J, Wang X, Zhang T, Zhao M, Li H. Low vitamin D status is associated with coronavirus disease 2019 outcomes: a systematic review and meta-analysis. Int J Infect Dis. 2021 Mar;104:58-64. doi: 10.1016/j.ijid.2020.12.077. Epub 2021 Jan 2. PMID: 33401034; PMCID: PMC7833186.