There is a positive association between cigarette smoking and coronary heart disease (CHD) risk in women with type 2 diabetes. Quitting smoking decreases the excess risk substantially.
"Given that cigarette smoking is such a strong, yet modifiable, risk factor for CHD among diabetic individuals, doctors should discourage their diabetic patients from smoking," United States researchers say.
They explain: "Diabetes may increase the risk of CHD through various proposed mechanisms, including lipoprotein changes, increased vascular endothelial injury and permeability, thrombotic disorders, increased oxidative stress and fibrinolytic factors and platelet activities leading to atheroma formation.
"Smoking may exacerbate these conditions and contribute to a dramatically increased risk of CHD among diabetic persons by a combination of short-term effects and long-term effects on the cardiovascular system.
"Smoking is also thought to increase insulin resistance and aggravate metabolic disturbances among diabetic people."
Investigators from Harvard University and Brigham and Women’s Hospital in Boston, Massachusetts say the short-term effects are coronary artery spasm, arrhythmias and increased platelet aggregation. Long-term effects include increased triglyceride levels, decreased high-density lipoprotein levels and other metabolic effects that lead to atherogenesis.
"Cigarette amplified the excess risk of CHD associated with type 2 diabetes mellitus," they concluded.
"On the other hand, smokers who quit smoking for more than 10 years had a risk of developing CHD similar to that of diabetic women who had never smoked."
Researchers used data from the US Nurses’ Health Study to assess the relationship between cigarette smoking and risk of CHD among diabetic women. In the Nurses’ Health Study, 121,700 US female nurses were followed from July 1976 through July 1996. There were 6,547 women in the cohort diagnosed with type 2 diabetes mellitus.
"We documented 458 incident cases of CHD during 20 years (68,227 person-years) of follow-up," the researchers report.
There were 200 fatal CHD-related cases and 258 non-fatal myocardial infarctions in the group.
"Compared with never smokers, the relative risks for CHD were 1.21 for past smokers, 1.66 for current smokers of one to 14 cigarettes per day and 2.68 for current smokers of 15 or more cigarettes per day in multivariate analyses."
They point out their results indicate that diabetic women who smoke 15 or more cigarettes a day have an 84 percent higher risk of developing stroke than do diabetic women who never smoked.
Investigators note, however, the multivariate relative risk of CHD among diabetic women who had stopped smoking for 10 years is similar to that of diabetic women who never smoked.
"Benefits of smoking cessation are associated with total mortality rate, with CHD and stroke incidence among the Nurses" Health Study and general populations and, more recently, with CHD risk in the United Kingdom Prospective Diabetes Study cohort of diabetic people."
Archives of Internal Medicine, 2002; 162: 273-279.