Genetically predicted serum vitamin D and COVID-19: a Mendelian randomization study

ABSTRACT Objectives To investigate causality of the association of serum vitamin D with the risk and severity of COVID-19 infection. Design Two-sample Mendelian randomization study. Setting Summary: data from genome-wide analyses in the population-based UK Biobank and SUNLIGHT Consortium, applied to meta-analyzed results of genome-wide analyses in the COVID-19 Host Genetics Initiative. Participants 17,965 COVID-19 cases including 11,085 laboratory or physician confirmed cases, 7,885 hospitalized cases, and 4,336 severe respiratory cases, and 1,370,547 controls, primarily of European ancestry. Exposures Genetically predicted variation in serum vitamin D status, based on genome-wide significant single nucleotide polymorphisms (SNPs) associated with serum vitamin D or risk of vitamin D deficiency/insufficiency. Main outcome measures Susceptibility to and severity of COVID-19 infection, including severe respiratory infection and hospitalization. Results Mendelian randomization analysis, powered to detect moderate effects comparable to those seen in observational studies, provided little to no evidence for an effect of genetically predicted serum vitamin D on susceptibility to or severity of COVID-19 infection. Using SNPs in loci related to vitamin D metabolism as proxies for serum vitamin D concentration, the odds ratio for a standard deviation increase in serum vitamin D was 1.04 (95% confidence interval 0.92 to 1.18) for any COVID-19 infection versus population controls, 1.05 (0.84-1.31) for hospitalized COVID-19 versus population controls, 0.96 (0.64 to 1.43) for severe respiratory COVID-19 versus population controls, 1.15 (0.99 to 1.35) for COVID-19 positive versus COVID-19 negative, and 1.44 (0.75 to 2.78) for hospitalized COVID-19 versus non-hospitalized COVID-19. Results were similar in analyses that used all SNPs with genome-wide significant associations with serum vitamin D (i.e., including SNPs in loci with no known relationship to vitamin D metabolism) and in analyses using SNPs with genome-wide significant associations with risk of vitamin D deficiency or insufficiency. Conclusions These findings suggest that genetically predicted differences in long-term vitamin D nutritional status do not causally affect susceptibility to and severity of COVID-19 infection, and that associations observed in previous studies may have been driven by confounding. These results do not exclude the possibility of low-magnitude causal effects, nor do they preclude potential causal effects of acute responses to therapeutic doses of vitamin D. Future directions include extension of this work to non-European ancestry populations, and high-risk populations, for example persons with comorbid disease.