Department of Health Behavior, Roswell Park Comprehensive Cancer Center, Elm and Carlton Streets, Buffalo, NY, 14263, USA.
Department of Clinical and Translational Research, University of Rochester Medical Center School of Medicine and Dentistry, 601 Elmwood Ave, CU420708, Rochester, NY, 14642, USA.
Harm Reduct J. 2020 Nov 23;17(1):91. doi: 10.1186/s12954-020-00440-w.
Electronic cigarettes (e-cigarettes) are widely promoted as harm-reduction products for smokers, and smokers commonly perceive them as less harmful than combustible cigarettes. One of the key questions regarding public health consequences of e-cigarettes is the magnitude of harm reduction achievable by smokers who switch from combustible cigarettes to e-cigarettes. We conducted a systematic literature review of epidemiological studies that estimated odds of respiratory and cardiovascular outcomes among former smokers who use e-cigarettes compared to current smokers.
This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) statement. We searched the PubMed and Embase databases in September 2020 to identify epidemiological studies that compared odds of cardiovascular and respiratory outcomes among former smokers who transitioned to e-cigarettes relative to odds among current smokers not using e-cigarettes (current exclusive smokers). We included studies that provided direct estimates of relevant odds ratios (ORs). We also included studies where indirect estimates of relevant ORs could be calculated based on published results. Two reviewers independently extracted data and conducted quality appraisals.
Six population-based studies with sample sizes ranging from 19,475 to 161,529 respondents met review inclusion criteria, five of which were cross-sectional and one longitudinal. Three studies reported respiratory outcomes and three reported cardiovascular outcomes. ORs of respiratory outcomes (including chronic obstructive pulmonary disease, chronic bronchitis, emphysema, asthma, and wheezing) in former smokers who transitioned to e-cigarettes versus current exclusive smokers were below 1.0, ranging from 0.58 (95%CI 0.36-0.94) to 0.66 (95%CI 0.50-0.87; all p < 0.05). All ORs for cardiovascular outcomes (including stroke, myocardial infarction, and coronary heart disease) did not differ significantly from 1.0.
Though our review included a small number of studies, it provided consistent results. Former smokers who transitioned to e-cigarettes showed ~ 40% lower odds of respiratory outcomes compared to current exclusive smokers. Switching from smoking to e-cigarette does not appear to significantly lower odds of cardiovascular outcomes. Since the utility of cross-sectional studies for causal inference remains limited, both randomized controlled trials and prospective cohort studies are needed to better evaluate contributions of e-cigarettes as harm reduction tools for smokers.
电子烟作为吸烟者的减害产品被广泛推广，吸烟者普遍认为它们比可燃香烟危害小。关于电子烟对公共健康后果的一个关键问题是，从可燃香烟转为电子烟的吸烟者能够实现多大程度的减害。我们对评估了曾使用电子烟的戒烟者与当前不使用电子烟（即当前仅吸可燃香烟者）的吸烟者相比，前者出现呼吸和心血管结局的几率的流行病学研究进行了系统性文献回顾。
本系统性综述按照系统评价和荟萃分析的首选报告项目（PRISMA）声明进行。我们于 2020 年 9 月在 PubMed 和 Embase 数据库中检索了比较曾使用电子烟的戒烟者与当前不使用电子烟的吸烟者相比出现心血管和呼吸结局几率的流行病学研究。我们纳入了提供相关比值比（OR）直接估计值的研究。我们还纳入了可以根据发表结果计算相关 OR 间接估计值的研究。两名审查员独立提取数据并进行质量评估。
纳入了六项符合综述纳入标准的研究，样本量从 19475 到 161529 名应答者不等，其中五项为横断面研究，一项为纵向研究。三项研究报告了呼吸结局，三项研究报告了心血管结局。与当前仅吸可燃香烟者相比，曾使用电子烟的戒烟者出现呼吸结局（包括慢性阻塞性肺疾病、慢性支气管炎、肺气肿、哮喘和喘息）的 OR 低于 1.0，范围为 0.58（95%CI 0.36-0.94）至 0.66（95%CI 0.50-0.87；均 < 0.05）。所有心血管结局（包括中风、心肌梗死和冠心病）的 OR 均与 1.0 无显著差异。
尽管我们的综述纳入的研究数量较少，但结果一致。与当前仅吸可燃香烟者相比，曾使用电子烟的戒烟者出现呼吸结局的几率低约 40%。从吸烟转为电子烟似乎不会显著降低心血管结局的几率。由于横断面研究用于因果推断的实用性仍然有限，因此需要随机对照试验和前瞻性队列研究来更好地评估电子烟作为吸烟者减害工具的作用。
