title: Investigating causality in the association between 25(OH)D and schizophrenia.
abstract: Vitamin D deficiency is associated with increased risk of schizophrenia. However, it is not known whether this association is causal or what the direction of causality is. We performed two sample bidirectional Mendelian randomization analysis using single nucleotide polymorphisms (SNPs) robustly associated with serum 25(OH)D to investigate the causal effect of 25(OH)D on risk of schizophrenia, and SNPs robustly associated with schizophrenia to investigate the causal effect of schizophrenia on 25(OH)D. We used summary data from genome-wide association studies and meta-analyses of schizophrenia and 25(OH)D to obtain betas and standard errors for the SNP-exposure and SNP-outcome associations. These were combined using inverse variance weighted fixed effects meta-analyses. In 34,241 schizophrenia cases and 45,604 controls, there was no clear evidence for a causal effect of 25(OH)D on schizophrenia risk. The odds ratio for schizophrenia per 10% increase in 25(OH)D conferred by the four 25(OH)D increasing SNPs was 0.992 (95% CI: 0.969 to 1.015). In up to 16,125 individuals with measured serum 25(OH)D, there was no clear evidence that genetic risk for schizophrenia causally lowers serum 25(OH)D. These findings suggest that associations between schizophrenia and serum 25(OH)D may not be causal. Therefore, vitamin D supplementation may not prevent schizophrenia.
authors.affiliation: MRC Integrative Epidemiology Unit (IEU) at the University of Bristol, UK.|UK Centre for Tobacco and Alcohol Studies, University of Bristol, UK.|School of Experimental Psychology, University of Bristol, UK.
authors.forename: Amy E
authors.initials: AE
authors.lastname: Taylor
authors.affiliation: MRC Integrative Epidemiology Unit (IEU) at the University of Bristol, UK.|Department of Public Health and Primary Care, University of Cambridge, UK.
authors.forename: Stephen
authors.initials: S
authors.lastname: Burgess
authors.affiliation: MRC Integrative Epidemiology Unit (IEU) at the University of Bristol, UK.|UK Centre for Tobacco and Alcohol Studies, University of Bristol, UK.|School of Social and Community Medicine, University of Bristol, UK.
authors.forename: Jennifer J
authors.initials: JJ
authors.lastname: Ware
authors.affiliation: MRC Integrative Epidemiology Unit (IEU) at the University of Bristol, UK.|UK Centre for Tobacco and Alcohol Studies, University of Bristol, UK.|School of Experimental Psychology, University of Bristol, UK.
authors.forename: Suzanne H
authors.initials: SH
authors.lastname: Gage
authors.affiliation: Centre for Clinical Epidemiology, Lady Davis Institute for Medical Research, Jewish General Hospital, McGill University, Canada.|Department of Medicine, McGill University, Canada.|Department of Twin Research, King's College London, UK.
authors.forename: J Brent
authors.initials: JB
authors.lastname: Richards
authors.affiliation: MRC Integrative Epidemiology Unit (IEU) at the University of Bristol, UK.|School of Social and Community Medicine, University of Bristol, UK.
authors.forename: George
authors.initials: G
authors.lastname: Davey Smith
authors.affiliation: MRC Integrative Epidemiology Unit (IEU) at the University of Bristol, UK.|UK Centre for Tobacco and Alcohol Studies, University of Bristol, UK.|School of Experimental Psychology, University of Bristol, UK.
authors.forename: Marcus R
authors.initials: MR
authors.lastname: Munafò
mesh_terms: D016022:Case-Control Studies; D005260:Female; D020022:Genetic Predisposition to Disease; D055106:Genome-Wide Association Study; D006801:Humans; D008297:Male; D057182:Mendelian Randomization Analysis; D015201:Meta-Analysis as Topic; D016017:Odds Ratio; D020641:Polymorphism, Single Nucleotide; D012559:Schizophrenia / Q000150:complications / Q000235:genetics*; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D