Interaction of diabetes and smoking on stroke: A population-based cross-sectional survey in China

Objectives Diabetes and smoking are known independent risk factors for stroke; however, their interaction concerning stroke is less clear. We aimed to explore such interaction and its influence on stroke in Chinese adults. Design Cross-sectional study. Setting Community-based investigation in Xuzhou, China. Participants A total of 39,887 Chinese adults who fulfilled the inclusion criteria were included. Methods Participants were selected using a multi-stage stratified cluster method, and completed self-reported questionnaires on stroke and smoking. Type 2 diabetes mellitus (DM2) was assessed by fasting blood glucose or use of antidiabetic medication. Interaction, relative excess risk owing to interaction (RERI), attributable proportion (AP), and synergy index (S) were evaluated using a logistic regression model. Results After adjustment for age, sex, marital status, educational level, occupation, physical activity, body mass index, hypertension, family history of stroke, alcohol use, and blood lipids, the relationships between DM2 and stroke, and between smoking and stroke, were still significant: odds ratios were 2.75 (95% confidence interval [CI]: 2.03–3.73) and 1.70 (95% CI: 1.38–2.10), respectively. In subjects with DM2 who smoked, the RERI, AP, and S values (and 95% CIs) were 1.80 (1.24–3.83), 0.52 (0.37–0.73), and 1.50 (1.18–1.84), respectively. Conclusions The results suggest there are additive interactions between DM2 and smoking and that these affect stroke in Chinese adults. Article Summary: Strengths and limitations of this study The strengths of this study were that a large sample population was randomly selected from the general population of Xuzhou and many confounding risk factors were adjusted for. Owing to the cross-sectional design, we could not determine a causal combined relationship among diabetes, smoking and stroke. We were not able to control for some important and well-known risk factors of diabetes, such as heart rate and cardiovascular causes. We did not measure fresh fruit consumption, which is causally related to stroke.