Smokeless Tobacco Use and Circulatory Disease Risk: a Systematic Review and Meta-Analysis
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Open access Meta-analysis Open Heart: first published as 10.1136/openhrt-2018-000846 on 8 October 2018. Downloaded from Smokeless tobacco use and circulatory disease risk: a systematic review and meta-analysis Brian L Rostron, Joanne T Chang, Gabriella M Anic, Manju Tanwar, Cindy M Chang, Catherine G Corey To cite: Rostron BL, Chang JT, ABSTRACT Key questions Anic GM, et al. Smokeless Objective Smokeless tobacco use is a public health tobacco use and circulatory issue throughout the world, but reviews and analyses disease risk: a systematic What is already known about this subject? of circulatory disease risks associated with smokeless review and meta-analysis. Open ► Smokeless tobacco use is known to pose numerous tobacco use may be outdated or incomplete. This study Heart 2018;5:e000846. health risks, but reviews and analyses of circulatory provides a thorough and comprehensive review and doi:10.1136/ disease risks in high-income countries may be out- meta-analysis of circulatory disease risks in high-income openhrt-2018-000846 dated or incomplete. countries, including recently published study estimates. Methods We conducted a systematic review of studies What does this study add? Received 2 May 2018 of circulatory disease risks associated with smokeless ► This study finds that US smokeless tobacco users Revised 24 July 2018 tobacco use in Europe and North America that were have increased risks of heart disease and stroke Accepted 22 August 2018 identified from electronic databases and reference lists. compared with non-users, although it did not ob- Study estimates were extracted by region, smokeless serve increased risk among Swedish smokeless tobacco use status, cigarette smoking status, and users. circulatory condition and combined in meta-analysis using a random-effects model. We used the Newcastle-Ottawa How might this impact on clinical practice? scale to assess study quality and risk of bias. ► Practitioners should advise their patients who use Results We identified 17 relevant cohort studies, two smokeless tobacco products of the known health pooled analyses, five case–control studies and one risks and provide advice on cessation. cross-sectional analysis. We found increased risk of heart disease (relative risk (RR) 1.17, 95% CI 1.09 to http://openheart.bmj.com/ 1.27) and stroke (RR 1.28, 95% CI 1.01 to 1.62) among identified. Moreover, disease burden calcula- US smokeless tobacco users compared with non-users. tions for smokeless tobacco in the USA are Increased circulatory disease risk was not observed generally unavailable for these conditions. among Swedish smokeless tobacco users. Several reviews of smokeless tobacco Conclusion US smokeless tobacco users were found to use and circulatory disease risk have been have increased risk of heart disease and stroke. conducted previously. Lee2 reviewed 11 studies from Sweden and the USA in 2007 and found an association between smoke- less tobacco use and increased heart disease on September 27, 2021 by guest. Protected copyright. INTRODUCTION risk based on eight studies, increased stroke The health effects of smokeless tobacco use risk based on five studies and increased are of considerable research and public overall circulatory disease risk based on health interest. Globally, more than 300 three studies. Boffetta and Straif3 also iden- million people use these products, many of tified 11 observational studies from Sweden them in low-income countries.1 In the USA, and the USA in 2009 and found an associ- © Author(s) (or their it has been estimated that smokeless tobacco ation between smokeless tobacco use and employer(s)) 2018. Re-use use was responsible for approximately 1600 increased risk of fatal myocardial infarction permitted under CC BY-NC. No new cases of oral cancer, 500 new cases of based on eight studies and increased risk of commercial re-use. See rights pancreatic cancer and 200 new cases of fatal stroke based on five studies. Zhang et al4 and permissions. Published 1 by BMJ. oesophageal cancer in 2008. Although identified eight studies from Asian countries, Center for Tobacco Products, some types of smokeless tobacco have been principally Bangladesh, India and Taiwan in Food and Drug Administration, found to be associated with circulatory condi- 2010. They found increased cardiovascular Silver Spring, Maryland, USA tions including heart disease and stroke,2 3 and ischaemic heart disease risk based on comprehensive reviews of this association in six studies and increased cerebrovascular Correspondence to Dr Brian L Rostron; brian. high-income countries may be out of date or risk based on three studies for ever users of rostron@ fda. hhs. gov limited by the number of study estimates they chewing substances with and without tobacco. Rostron BL, et al. Open Heart 2018;5:e000846. doi:10.1136/openhrt-2018-000846 1 Open Heart Open Heart: first published as 10.1136/openhrt-2018-000846 on 8 October 2018. Downloaded from Siddiqi et al5 reviewed 13 studies of heart disease and terms for each database. Two reviewers (GMA and JTC) stroke risk from South Asia and Sweden in 2015 and did independently reviewed the titles and abstracts of these not observe increased risk in Swedish studies. They noted articles and identified relevant references for further that the multicountry INTERHEART study with data from review. Each reviewer then evaluated each reference for 52 countries found increased heart disease risk among inclusion in the study. We searched for relevant unpub- smokeless tobacco users. Vidyasagaran et al6 reviewed 20 lished studies by reviewing previous reviews and the refer- studies from South Asia, Sweden and the USA in 2016 ence lists of selected articles. Preliminary studies by two and found increased mortality risk from ischaemic heart groups of researchers14–16 were identified in our search disease and stroke among ever smokeless tobacco users. but were not included in the review because they have Results varied by region, with a significant association for yet to be published. The rationale for their exclusion non-fatal ischaemic heart disease in Asian but not Euro- is explained in greater detail in the Discussion section. pean studies. Sinha et al7 identified 16 studies of all-cause The reviewers then extracted relevant information from and cause-specific mortality risk from South Asia, Sweden identified studies including study design, country, study and the USA in 2018. They found smokeless tobacco use size, smokeless tobacco type, and circulatory conditions to be associated with increased mortality risk for all causes or mortality outcomes. Because studies often report more as well as ischaemic heart disease and stroke. Gupta et al8 than one estimate, specific estimates for each outcome reviewed 20 studies from South Asia, Iran, Sweden and from each study were extracted using the following the USA, also in 2018, and found an association between order of preference lists: smokeless tobacco type (all, smokeless tobacco use and fatal coronary heart disease in snuff or snus, chewing tobacco), smokeless tobacco Swedish studies and studies overall. use status (current or former, ever), cigarette smoking Several reviews of smokeless tobacco use and circula- status (never, non-current, any smoking status), medical tory disease risks have thus been published, but these outcome (specific circulatory conditions such as heart reviews have varied in terms of the geographical areas disease or stroke, all circulatory conditions), outcome and smokeless tobacco products they covered, the studies type (all cases, then fatal or non-fatal events for the type they included and the findings they reported. In addi- that has the greater number of cases) and adjustment for tion, new studies on this topic have been published.9–11 other risk factors (the most extensive adjustment avail- The aim of this study therefore is to produce an updated able). Medical outcomes were categorised as ischaemic systematic review and meta-analysis of smokeless tobacco heart disease (conditions included in International use and circulatory disease risks, specifically focusing on Classification of Diseases (ICD)-9 410–414, sometimes studies conducted among European and North American characterised as myocardial infarction, coronary heart smokeless tobacco users. These regions were selected disease or cardiovascular disease in specific studies), because products from these areas, such as chewing stroke (ICD-9 430–438) and other circulatory condi- http://openheart.bmj.com/ tobacco, moist snuff and snus, are commonly sold in the tions (the remainder of ICD-9 390–459). The quality of US market and thus regulated by the US Food and Drug these studies was also assessed using the Newcastle-Ot- Administration. Moreover, smokeless tobacco products tawa scale, a standardised scale to assess the quality of from other areas such as South Asia and Africa can be non-randomised studies included in systematic reviews quite different in terms of product characteristics and and meta-analyses.17 Studies were assigned a maximum health risks from products sold in the USA.12 This review of nine stars based on established criteria for the selec- covers circulatory conditions including heart disease, tion of study groups, the comparability of groups and stroke and other circulatory conditions. the ascertainment of exposure for case–control studies and outcome for cohort studies. Additional information on September 27, 2021 by guest. Protected copyright. about the scale and its criteria are provided in online METHODS