Dual impact of smoking cessation and post‐cessation weight change on psoriasis

Background The impact of post‐cessation weight changes on the preventive effect of smoking cessation on psoriasis remains unknown. Objectives To examine the association between smoking cessation, subsequent weight changes measured using body mass index (BMI), risks of psoriasis vulgaris (PsV), palmoplantar pustulosis (PPP) and generalized pustular psoriasis (GPP). Methods This nationwide cohort study, performed using the Korean National Health Insurance Service database, included 5,470,955 participants who underwent two consecutive biennial health screenings from 2004 to 2005 and 2006 to 2007. Data on changes in smoking habits and BMI status were obtained from these health screenings. The Cox proportional hazards model was utilized to estimate the risk of developing psoriasis based on changes in smoking habits and weight status. Results Over 73.7 million person‐years, 63,538 cases of psoriasis were identified, including 49,157 PsV, 9291 PPP and 2298 GPP cases. Smoking quitters without weight changes (adjusted hazard ratio [aHR] 0.85; 95% confidence interval [CI] 0.79–0.92) and those with weight loss (aHR 0.88; 95% CI 0.79–0.97) showed a lower risk of psoriasis, including PsV and PPP, compared to sustained smokers. However, post‐cessation weight gain attenuated the benefits of smoking cessation, particularly for PsV. Nevertheless, the protective effect of smoking cessation on PPP remained substantial even in quitters with weight gain (aHR 0.67; 95% CI 0.57–0.79). In sensitivity analyses considering the time‐varying characteristics of smoking status and weight changes and examining the long‐term effects of smoking cessation, a notable decrease in the risk of psoriasis, including PsV and PPP, was identified regardless of post‐cessation weight change. Conclusions Despite post‐cessation weight gain, smoking cessation should be encouraged to prevent psoriasis, and weight management is recommended to maximize the health benefits of quitting smoking for psoriasis.