Comparative disease risks associated with cigarette smoking and use of moist smokeless tobacco and snus: an umbrella review of epidemiological evidence from the United States and Western Europe.

backgroundCigarette smoking causes many serious diseases, including lung cancer, Chronic Obstructive Pulmonary Disease (COPD), mouth cancer, and tobacco-related heart disease. For adults who smoke and are unable or unwilling to quit all tobacco, switching completely from cigarettes to lower-risk smoke-free tobacco products, may reduce the health risks associated with tobacco use. In this review, we summarize epidemiological findings and provide evidence about the potential risk differential between cigarette smoking and the use of oral smoke-free tobacco products used in the US, Sweden, and Norway. Due to the wide range of compositions and health risks associated with ST products around the world and to provide evidence most relevant to the US and Western European populations, we focused on epidemiological studies conducted in these regions only.

methodsWe used a two-stage approach to obtain recent risk estimates from relevant publications. First, we identified relevant meta-analyses and systematic reviews published from Jan. 2000- Feb. 2022. Second, we identified relevant individual studies published subsequent to the most recent meta-analysis or systematic review. Studies were selected using pre-defined inclusion/exclusion criteria. All eligible studies were assessed using National Heart, Lung, and Blood Institute Study Quality Assessment Tools. The relative risk estimates (RR) are reported compared to nonusers.

resultsOur search identified 25 systematic reviews. Meta-analyses consistently showed large and statistically robust RRs for cigarette smoking and lung cancer (i.e., RR ranging from 10.1 to 14.6), whereas no statistically significant associations (null associations) were observed for ST products used in the US, Sweden, and Norway, congruent with the lack of pulmonary exposure with the use of oral tobacco products. For COPD, mouth cancer, and heart diseases, we consistently observed higher RRs for cigarette smoking compared to using these ST products. Findings from individual studies are generally in line with these results. Importantly, a few studies documented those individuals who stopped cigarette smoking and used ST products from these regions (i.e., individuals who switched) had lower risks of lung cancer, mouth cancer, and heart diseases compared to those who continued to smoke. We identified no such studies for COPD, yet the risk estimates were generally comparable between those who switched and those who quit all tobacco products.

conclusionFindings from our literature review suggest that, relative to continued smoking, switching from cigarette smoking to the ST products commonly used in the US, Sweden, and Norway is associated with reduced risks of lung cancer, mouth cancer, COPD, and tobacco-related heart diseases. Future longitudinal studies that directly measure switching behavior will provide further evidence about the potential benefits of switching and the magnitude of the harm reduction potential.