Akbar et al., Front. Nutr. 8:660420,
doi:10.3389/fnut.2021.660420 (Peer Reviewed) (meta analysis)
Low Serum 25-hydroxyvitamin D (Vitamin D) Level Is Associated With Susceptibility to COVID-19, Severity, and Mortality: A Systematic Review and Meta-Analysis
Systematic review and meta analysis showing that low vitamin D levels was associated with COVID-19 cases, severity, and mortality.
Akbar et al., 3/29/2021, peer-reviewed, 4 authors.