Diabetes, prior CHD may not be equivalent CHD risk factors, study indicates

Diabetes and previous coronary heart disease (CHD) may not be equivalent risk factors for future CHD events, according to a recent study.

Researchers performed a population-based prospective cohort analysis of adults who were members of Kaiser Permanente North California to compare CHD risk among those with and without a history of diabetes or CHD. Hazard ratios for CHD were calculated for 4 groups according to baseline risk: no diabetes or previous CHD, only previous CHD, only diabetes, and both diabetes and previous CHD. The study results were published online Dec. 14, 2015, by the Journal of General Internal Medicine.

A total of 1,586,061 adults 30 to 90 years of age were included in the study. Most patients (88.6%) did not have either diabetes or CHD at baseline, 2.7% had previous CHD only, 7.5% had diabetes only, and 1.2% had both previous CHD and diabetes. Over the median follow-up period of 9.9 years, 80,012 new CHD events occurred. Hazard ratios for new CHD events were 2.8 (95% CI, 2.7 to 2.95) in patients with CHD alone at baseline, 1.7 (95% CI, 1.66 to 1.74) in those with diabetes alone, and 3.9 (95% CI, 3.8 to 4.0) in those with both diabetes and CHD, compared with patients who had neither risk factor. Risk for CHD in all age and sex groups was significantly lower in patients with diabetes alone versus those with CHD alone (12.2 per 1,000 person-years vs. 22.5 per 1,000 person-years). A similar risk for CHD events was seen in those with diabetes and those with previous CHD only in patients who had had diabetes for 10 years or longer.

The authors noted that CHD history and events were based on data from electronic medical records, that they could not account for lifetime risk of diabetes, and that the study population involved patients from a single health care delivery system, among other limitations. However, they concluded that diabetes alone and history of CHD alone did not confer similar risk for future CHD events. Compared to patients without either diabetes or CHD, the risk appeared to be doubled in those with the former and tripled in those with the latter, they said. Patients who had diabetes of longer duration (≥10 years) did have a CHD risk equivalent to those with previous CHD, and younger patients with diabetes (that is, those under age 40) had very low CHD event rates.

“These observational data are not sufficient to recommend modifications in any treatment recommendations,” the authors wrote, “but they are important for informing expectations of the natural history of these two chronic conditions.”