Cohort study of 18,148 patients in the USA showing low vitamin D associated with COVID-19 PCR+ status before adjustments but not after.
Authors state that "low vitamin D levels were not independently associated with the
risk of seropositivity", however there is significant correlation between some adjustment variables and vitamin D levels in the logistic regression that prevent drawing this conclusion . Details of the logistic regression in the matched sample set are not provided.
Authors analyze only 20ng/mL and 30ng/mL cutoff points, other studies use 10ng/mL (or 12), where more significant differences are typically seen.
Li et al., 5/19/2021, retrospective, USA, North America, peer-reviewed, 4 authors.
risk of COVID-19 case, 8.6% lower, RR 0.91, p = 0.21, high D levels 610 of 13650 (4.5%), low D levels 290 of 4498 (6.4%), adjusted per study, odds ratio converted to relative risk, >20ng/mL, Figure 2.
risk of COVID-19 case, 12.4% lower, RR 0.88, p = 0.06, high D levels 289 of 7272 (4.0%), low D levels 611 of 10876 (5.6%), adjusted per study, odds ratio converted to relative risk, >30ng/mL, Figure 2.
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.