Relation of Smoking With Total Mortality and Cardiovascular Events Among Patients With Diabetes Mellitus: A Meta-Analysis and Systematic Review

Abstract

Background: The prevalence of smoking in diabetic patients remains high, and reliable quantification of the excess mortality and morbidity risks associated with smoking is important for diabetes management. We performed a systematic review and meta-analysis of prospective cohort studies to evaluate the relation of active smoking with risk of total mortality and cardiovascular events among diabetic patients.

Methods and results: We searched Medline and Embase databases through May 2015, and multivariate-adjusted relative risks were pooled by using random-effects models. A total of 89 cohort studies were included. The pooled adjusted relative risk (95% confidence interval) associated with smoking was 1.55 (1.46-1.64) for total mortality (48 studies with 1,132,700 participants and 109,966 deaths), and 1.49 (1.29-1.71) for cardiovascular mortality (13 studies with 37,550 participants and 3163 deaths). The pooled relative risk (95% confidence interval) was 1.44 (1.34-1.54) for total cardiovascular disease (16 studies), 1.51 (1.41-1.62) for coronary heart disease (21 studies), 1.54 (1.41-1.69) for stroke (15 studies), 2.15 (1.62-2.85) for peripheral arterial disease (3 studies), and 1.43 (1.19-1.72) for heart failure (4 studies). In comparison with never smokers, former smokers were at a moderately elevated risk of total mortality (1.19; 1.11-1.28), cardiovascular mortality (1.15; 1.00-1.32), cardiovascular disease (1.09; 1.05-1.13), and coronary heart disease (1.14; 1.00-1.30), but not for stroke (1.04; 0.87-1.23).

Conclusions: Active smoking is associated with significantly increased risks of total mortality and cardiovascular events among diabetic patients, whereas smoking cessation is associated with reduced risks in comparison with current smoking. The findings provide strong evidence for the recommendation of quitting smoking among diabetic patients.

Keywords: diabetes mellitus; epidemiology; follow-up studies; meta-analysis; smoking.

Figure 1

Flowchart of the Meta-analysis.

Figure 2

Adjusted Relative Risks of Smoking with Total Mortality among Diabetic Participants. The summary estimates were obtained using a random-effects model. The data markers indicate the adjusted relative risks (RRs) comparing smoking to no smoking. The size of the data markers indicates the weight of the study, which is the inverse variance of the effect estimate. The diamond data markers indicate the pooled RRs. CI indicates confidence interval.

Figure 3

Adjusted Relative Risks of Smoking with (A) Cardiovascular Mortality and (B) Total Cardiovascular Disease among Diabetic Participants. The summary estimates were obtained using a random-effects model. The data markers indicate the adjusted relative risks (RRs) comparing smoking to no smoking. The size of the data markers indicates the weight of the study, which is the inverse variance of the effect estimate. The diamond data markers indicate the pooled RRs. CI indicates confidence interval.

Figure 4

Adjusted Relative Risks of Smoking with (A) Coronary Heart Disease and (B) Stroke among Diabetic Participants. The summary estimates were obtained using a random-effects model. The data markers indicate the adjusted relative risks (RRs) comparing smoking to no smoking. The size of the data markers indicates the weight of the study, which is the inverse variance of the effect estimate. The diamond data markers indicate the pooled RRs. CI indicates confidence interval.