Secondhand Smoke Exposure and the Risk of Chronic Obstructive Pulmonary Disease: A Systematic Review and Meta-Analysis

Background: Many studies have shown that active smoking leads to an increasing incidence of chronic obstructive pulmonary disease (COPD). However, studies interested in the effects of secondhand smoke exposure (SHS exposure) on COPD were less or underappreciated. Methods: A systematic review and meta-analysis was conducted to investigate the association between SHS exposure and the risk of COPD. Three databases (PubMed, Embase and Web of Science) were searched to obtain data. After assessing the study quality, stratified analyses were performed according to the region, gender, and duration of exposure. Cochran's Q and I2 were utilized for heterogeneity assessment. To assess publication bias, we used a funnel plot and Egger's test. Results: A total of 15 studies (6 cross-sectional studies, 6 case-control studies, and 3 cohort studies) with 25,592 participants were involved in this meta-analysis. This study showed that SHS exposure was associated with an increased risk of COPD (odds ratio (OR): 2.25, 95% CI: 1.40-3.62, I2 = 98%, p < 0.01 for heterogeneity based on a random-effects analysis model), especially in those with a longer time exposure of more than 5 years was 4.38 (95% CI: 1.28-15.00, I2 = 89%, p < 0.01 for heterogeneity based on a random-effects analysis model). In addition, SHS exposure also increases the risk of COPD in women (odds ratio (OR): 2.02, 95% CI: 1.52- 2.67, I2 = 0%, p = 0.89 for heterogeneity based on a random-effects analysis model). Conclusion: The findings suggest that SHS exposure is associated with the risk of COPD, especially for individuals with a long time exposed.