Temporal association of reduced serum vitamin D with COVID-19 infection: A single-institution case-control and historical cohort study
Abstract
Objectives
Vitamin D supplementation has been proposed for the prevention and treatment of COVID-19, but the relationship between the two is inconclusive: Reduced serum vitamin D may predispose to COVID-19, but it may also be a secondary consequence of infection. The objective of this study was to assess the temporal association between serum vitamin D levels and COVID-19.
Design
A single-institution case-control study and a historical cohort study
Setting
University of California San Diego (UCSD) Health System in San Diego, California
Participants
Patients testing positive for COVID-19 from January 1, 2020 to September 30, 2020 with serum 25-hydroxy-vitamin D (25(OH)D) measured within 180 days of diagnosis. Patients were separated based on whether 25(OH)D was measured before (n=107; “pre-diagnosis”) or after (n=203; “post-diagnosis”) COVID-19 diagnosis. Subjects with 25(OH)D assessments prior to COVID-19 diagnosis were evaluated using a case-control study design, while subjects with 25(OH)D measured after COVID-19 diagnosis were analyzed with a historical cohort study design.
Primary and Secondary Outcome Measures
In the pre-diagnosis study, a conditional logistic regression was performed using COVID-19 infection status as the binary dependent variable. In the post-diagnosis study, an ordinary least squares regression was performed using serum 25(OH)D levels as the continuous dependent variable.
Results
Serum 25(OH)D levels were not associated with the odds of subsequently testing positive for COVID-19 (OR 1.00, 95% CI: 0.98 to 1.02, p = 0.982). However, COVID-19 positive individuals had serum 25(OH)D measurements that were lower by 2.70 ng/mL (95% CI: −5.19 to −0.20, p = 0.034) compared to controls.
Conclusions
In our study population, serum 25(OH)D levels were not associated with risk of testing positive for COVID-19 but were reduced in subjects after being diagnosed with COVID-19 infection. These results raise the possibility that reduced serum 25(OH)D may be a consequence and not a cause of COVID-19 infection.
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