Men with type 2 diabetes mellitus and no cardiovascular disease and men who experience a first acute cardiovascular event were found to have similar long-term cardiovascular and total mortality risks in a large, longitudinal study.
In addition, the risk of cardiovascular death was more than three times greater for men in either group, compared with matched controls with neither diabetes nor cardiovascular disease, Dr. Gilles R. Dagenais of the University Laval, Quebec City, and his associates reported in the Canadian Medical Association Journal (2009;180:40–7 [doi:10.1503/cmaj.071027]).
They looked at the issue of whether diabetes alone is associated with a similar long-term increase in cardiovascular mortality risk, compared with a first cardiovascular event. There is no consensus in the literature, with some studies supporting the association (Lancet 2006;368:29–36; Diabetes Care 2005;28:1588–9) and others not (Circulation 2004;109:855–60; BMJ 2002;324:939–42).
The current study differed from previous research, because it looked at incident cases of diabetes and cardiovascular disease instead of prevalence. In addition, the study also excluded men with previous angina or intermittent claudication, conditions known to increase cardiovascular disease risk.
Dr. Dagenais and his colleagues at University Laval and the University of Montreal assessed 4,376 men at baseline in 1973 or 1974 and over time. The men were participants in the longitudinal Quebec Cardiovascular Study and were aged 35–64 years at entry in the current study. Blood pressure, cholesterol levels, family history of coronary artery disease and stroke, self-reported smoking status, and other factors were assessed in person in 1980 and 1985 and via standardized telephone or mail questionnaires in 1990 and in 1997 or 1998.
During the 24 years of follow-up, 137 men had a new diagnosis of type 2 diabetes without any previous cardiovascular disease. Another group of 527 men without diabetes experienced a first nonfatal cardiovascular event. Events included myocardial infarction in 354 patients, unstable angina in 58 men, and stroke in 115. Researchers compared survival with an age-matched group of 627 controls without diabetes or a cardiovascular event.
A total of 18 men experienced both a new diagnosis of diabetes and a cardiovascular event during the study. This group, however, was excluded from survival comparisons because of its small number.
The researchers found that men with cardiovascular disease only had a significantly higher risk of cardiovascular death during the first 5 years, compared with those with diabetes only (age-adjusted relative risk 2.03). Thereafter, researchers found no statistically significant difference in cardiovascular or total mortality between the two groups. “A longer duration of diabetes likely aggravates the atherothrombotic process that is associated with diabetes,” the authors wrote.
The study highlights the high risk of death associated with diabetes and underscores “the importance of optimal management of this disease and its associated cardiovascular conditions, as well as the importance of pursuing research to prevent type 2 diabetes altogether,” the researchers wrote.
A total of 23% of men with diabetes and no cardiovascular disease had a cardiovascular-related death during follow-up, compared with 7% of controls (RR 3.11). In addition, death from any cause occurred in 44% of this group, compared with 22% of controls (RR 1.89).
In the group of men with incident cardiovascular disease and no diabetes, 25% experienced cardiovascular death during follow-up (RR 4.46). In addition, 38% died from any cause (RR 2.19).
The authors noted some caveats and limitations, including “major changes in risk factors” during the study period. For example, between 1974 and 1985, smoking declined from 74% to 30% for the group of men with diabetes. At the same time, blood pressure for these men declined from 146/90 mmHg to 138/81 mmHg. In addition, smoking declined from 76% to 40% among men with cardiovascular disease.
Other limitations of the study included the fact that it consisted of white men only and that diabetes was self-reported by two-thirds of participants. Another limitation was that some men in the nodiabetes group may have had impaired fasting glucose or glucose intolerance, factors known to increase cardiovascular risk. Also, the research was conducted before important pharmacologic interventions to lower cardiovascular disease risk entered clinical practice, the authors noted.
The study was supported in part by the Heart and Stroke Foundation of Canada and an unrestricted grant from Sanofi-Aventis and Merck Frosst Canada Ltd. The authors reported no conflicts of interest.