The relationship between vitamin D deficiency and COVID-19 infection and mortality has been a hot topic for research, with a number of observational studies finding a strong correlation between the two.
This systematic review and meta-analysis included 27 observational studies that investigated vitamin D status in 8,176 people with COVID-19. The primary outcome was the correlation between vitamin D deficiency and COVID-19 severity, and the secondary outcomes were associations between vitamin D deficiency and COVID-19 infection, hospitalization, and mortality.
Vitamin D deficiency was not associated with COVID-19 infection risk, but people who had COVID-19 had lower vitamin D levels than people who did not. Additionally, 39% of people with COVID were vitamin D deficient. Of people with severe COVID-19, 65% were deficient. Vitamin D levels of less than 75 nmol/L were associated with an 81% increased risk of hospitalization and 82% increase in risk of death.
This study didn’t include much subgroup analysis, which would have been useful to see how outcomes differ when people are grouped by age, sex, and other categories. Additionally, the analyzed studies had very high study heterogeneity and risk of bias. While a systematic review and meta-analysis is a good way of critically analyzing the overall findings of a body of literature, it is only as good as the papers it includes.
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