Case control study with 201 patients and 201 matched controls in Iran showing vitamin D deficiency associated with COVID-19.
Abdollahi et al., 12/12/2020, retrospective, Iran, Middle East, peer-reviewed, 7 authors.
risk of COVID-19 case, 53.9% lower, RR 0.46, p = 0.001, high D levels 108, low D levels 294, >30ng/ml.
Effect extraction follows pre-specified rules
prioritizing more serious outcomes. For an individual study the most serious
outcome may have a smaller number of events and lower statistical signficance,
however this provides the strongest evidence for the most serious outcomes
when combining the results of many trials.