Excess risk of mortality and cardiovascular events associated with smoking among patients with diabetes: Meta-analysis of observational prospective studies

BackgroundNumerous studies have demonstrated that both smoking and diabetes are risk factors for mortality and caused-specific cardiovascular events. However, few studies systematically investigated to what extent the excess risk could be attributed to smoking among diabetic patients.MethodsLiterature references were searched up to April 2011 in MEDLINE and EMBASE, supplemented by manual searches. Inclusion criteria were prospective cohort studies, assessment of the association between smoking and total mortality, cardiovascular death, incidence of coronary heart disease (CHD), stroke and myocardial infarction (MI) in diabetic patients.ResultsOf 3758 studies in the literature searched, 46 were eligible with approximately 130,000 diabetic patients. The relative risk (RR) comparing smokers with nonsmokers was 1.48[95% confidential interval (CI): 1.34-1.64] for total mortality (27 studies), 1.36(1.22-1.52) for cardiovascular mortality (9 studies), 1.54(1.31-1.82) for CHD (13 studies), 1.44(1.28-1.61) for stroke (9 studies) and 1.52(1.25-1.83) for MI (7 studies). Furthermore, the excess risk was observed among former and current smokers with a greater risk in current smokers. Subgroup analysis showed that the increased risk appeared to be consistent regardless of several study characteristics with the RRs ranging from 1.31 to 1.94 for all-cause mortality, 1.37 to 2.28 for CHD, 1.21 to 1.87 for stroke, 1.13 to 1.74 for cardiovascular mortality and 1.15 to 2.01 for MI.ConclusionSmoking amplified the risk of mortality as well as cardiovascular events and the effect size for CHD appeared to be higher than other events in diabetic patients. Moreover, a trend of decreasing risk was observed among smoking quitters.