Diabetes Adds 15 Years to Heart Attack Risk Calculation

TORONTO, June 29 - Diabetes is the clinical equivalent of aging 15 years, thrusting men and women with the disease into a high-risk category for cardiovascular disease while still in middle-age.

A 48-year-old diabetic man has a 20% risk of suffering an acute myocardial infarction by age 58, wrote Gillian L. Booth, M.D., and colleagues, of the University of Toronto in the July 1 issue of The Lancet.

Similarly, a 54-year-old woman with diabetes has a one in five chance of having a heart attack before she reaches retirement age.

Moreover, women ages 20 to 34 who have diabetes have acute myocardial infarction rates that are nearly 40 times higher than their age-matched non-diabetic counterparts.

But that rate increase does not boost diabetic women in their 20s and 30s into the high-risk category for cardiovascular disease and their event rate is lower than the rate observed in non-diabetics who have established coronary heart disease.

Dr. Booth and colleagues conducted a retrospective cohort study of 379,003 adults with diabetes and 9,018,082 adults without diabetes living in the Canadian province of Ontario. The study included all Ontario residents who were age 20 or older on April 1, 1994, and followed them, recording all cardiovascular disease events until March 31, 2000.

The study did not distinguish between type 1 and type 2 diabetes.

The authors defined high risk as a fatal or non-fatal coronary heart disease event rate of equivalent to a 10-year risk of 20% or more or a rate equal to the risk in people who have already had a myocardial infarction.

In both diabetics and non-diabetics, the risk of heart disease increases with age, but for men and women with diabetes the transition from moderate to high risk occurred at about age 48 for men and 54 for women, which was 14.6 years earlier than transition in non-diabetics.

Diabetes also eliminated much, but not all, of the gender gap in heart disease. In non-diabetics the age-adjusted hazard ratio for incident acute myocardial infarction was 2.56 for men compared with women (95% CI 2.53-2.60); after adjusting for other risk factors, "men with diabetes were 1.22 times more likely to have an [acute myocardial infarction] than women with diabetes."

The data suggest that "young adults with diabetes have rates of [coronary heart disease] 12 to 40 times higher than those in people of the same age without diabetes. However, absolute rates of coronary events and [cardiovascular disease events] in general, were lower in this younger group than the rates conventionally regarded as high risk, and lower than those of people without diabetes with established [coronary heart disease]."

The study relied on medical records to identify people with diabetes, so it possible that the "use of our algorithm would not have identified people with undiagnosed diabetes." But that omission would have biased the study towards a null hypothesis, they wrote.

A second limitation is the failure to discern use of cardioprotective drugs in patients of all ages. But prescription records were available for people ages 65 or older, and from 1994 through 1999 only 8% to 25% of Ontario residents age 65 or older were taking lipid-lowering medications, and 25% to 37% were taking ACE inhibitors. Those rates indicate that it is unlikely that there was substantial use of those drugs in younger residents.

The authors concluded that "middle-age and older people with diabetes seem on average to be at high risk of [cardiovascular disease], thus aggressive risk-reduction strategies are warranted for them."

Younger people with diabetes appear to be at low to moderate risk, thus the data support present guidelines recommending that risk-reduction efforts be individualized in patients with diabetes who are younger than 40.