Smoking, but not alcohol consumption, is causally associated with psoriasis, according to a study published online June 28 in the British Journal of Dermatology .

Jiahe Wei, from Hangzhou Medical College in China, and colleagues examined the causal associations of alcohol consumption and smoking with psoriasis using genome-wide association study (GWAS) summary-level data for alcohol consumption, smoking initiation, cigarettes per day, and smoking cessation from the Sequencing Consortium of Alcohol and Nicotine use consortium and for lifetime smoking from the U.K. Biobank. Summary statistics for psoriasis were obtained from a recent GWAS meta-analysis of eight cohorts and the FinnGen consortium. Bidirectional Mendelian randomization (MR) analyses were performed to assess causal direction.

The researchers identified genetic correlations between smoking and psoriasis. A causal effect of smoking initiation, cigarettes per day, and lifetime smoking on psoriasis was revealed in MR (odds ratios [95 percent confidence intervals], 1.46 [1.32 to 1.60], 1.38 [1.13 to 1.67], and 1.96 [1.41 to 2.73], respectively). In addition, there was a suggestive causal effect of smoking cessation on psoriasis (odds ratio, 1.39; 95 percent confidence interval, 1.07 to 1.79). No causal relationship was identified between alcohol consumption and psoriasis.

"Our study provides genetic evidence supporting the causal effects of smoking on psoriasis risk, suggesting that restricting smoking could be helpful in reducing the burden of psoriasis," the authors write.

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