Smoking and risk of coronary heart disease among women with type 2 diabetes mellitus

Background: Although the association between smoking and increased risk of coronary heart disease (CHD) is well established in the general population, this relationship is less well-defined among individuals with diabetes. Objective: To assess the relationship between cigarette smoking and risk of CHD among women with type 2 diabetes mellitus in the Nurses' Health Study cohort. Methods: The Nurses' Health Study, a prospective cohort study of 121700 US female registered nurses surveyed in 11 states and followed up from July 1, 1976, through July 1, 1996, involved a total of 6547 women diagnosed as having type 2 diabetes mellitus. Incident cases of CHD were our main outcome measure in this study. Results: We documented 458 incident cases of CHD (200 fatal CHD-related cases and 258 nonfatal myocardial infarctions) during 20 years (68227 person-years) of follow-up. We found a dose-response relationship between current smoking status and risk of CHD among diabetic women. Compared with never smokers, the relative risks (RRs) for CHD were 1.21 (95% confidence interval [CI], 0.97-1.51) for past smokers, 1.66 (95% CI, 1.10-2.52) for current smokers of 1 to 14 cigarettes per day, and 2.68 (95% CI, 2.07-3.48) for current smokers of 15 or more cigarettes per day in multivariate analyses (P<.001 for trend). The multivariate RR of CHD among diabetic women who had stopped smoking for snore than 10 years was similar to that among diabetic women who were never smokers (RR, 1.01; 95% CI, 0.73-1.38). In secondary analyses involving diabetic and nondiabetic women, the multivariate-adjusted RR of CHD for those with diabetes who currently smoked (≥15 cigarettes per day) compared with those who never smoked was 7.67 (95% CI, 5.88-10.01). Conclusions: Cigarette smoking is strongly associated with an increased risk of CHD among women with type 2 diabetes mellitus. Furthermore, quitting smoking seems to decrease this excess risk substantially; women with diabetes should be strongly advised against smoking.