Alcohol consumption and smoking in relation to psoriasis: a Mendelian randomization study

Background Alcohol consumption and smoking have been reported to be associated with psoriasis risk. However, a conclusion with high‐quality evidence of causality could not be easily drawn from regular observational studies. Objectives This study aims to assess the causal associations of alcohol consumption and smoking with psoriasis. Methods Genome‐wide association study (GWAS) summary‐level data for alcohol consumption (N = 941 280), smoking initiation (N = 1 232 091), cigarettes per day (N = 337 334) and smoking cessation (N = 547 219) was obtained from the GSCAN consortium (Sequencing Consortium of Alcohol and Nicotine use). The GWAS results for lifetime smoking (N = 462 690) were obtained from the UK Biobank samples. Summary statistics for psoriasis were obtained from a recent GWAS meta‐analysis of eight cohorts comprising 19 032 cases and 286 769 controls and the FinnGen consortium, comprising 4510 cases and 212 242 controls. Linkage disequilibrium score regression was applied to compute the genetic correlation. Bidirectional Mendelian randomization (MR) analyses were conducted to determine casual direction using independent genetic variants that reached genome‐wide significance (P