Diabetes and prior CVD may no longer carry equivalent cardiovascular risk

Diabetes and prior cardiovascular disease (CVD) may no longer pose an equivalent risk of cardiovascular events, according to a retrospective study.

Researchers noted that between 1982 and 2000, patients with diabetes had the same risk of cardiovascular events as those with prior CVD. To see whether the risk equivalence persisted into more recent years, they used administrative health care data from Ontario, Canada, from 1994 to 2019. They created five separate population-based cohorts of adults ages 20 to 84 years who were alive on the index date (April 1) during 1994, 1999, 2004, 2009, and 2014 and selected a random sample of 25% of each cohort. The exposures were diabetes, prior CVD, or both on the index date, with those who had neither diabetes nor CVD serving as the reference group. The primary outcome was cardiovascular events, defined as a composite of hospitalization for acute myocardial infarction or stroke, or all-cause mortality, with up to five years of follow-up. Results were published as a research letter on Oct. 14 by JAMA.

The mean patient age increased from 44.4 to 47.5 years between 1994 and 2014, with a stable percentage of women (51%). The prevalence of diabetes and CVD increased from 3.1% (n=57,560) to 9.0% (n=225,611) and from 2.5% (n=46,103) to 3.7% (n=92,426), respectively, over the study period. In the 1994 cohort, having diabetes was associated with an increased risk of cardiovascular events (28.4 vs. 12.7 per 1,000 person-years; absolute risk increase [ARI], 4.4% [95% CI, 4.2% to 4.5%]; relative risk [RR], 2.06 [95% CI, 2.02 to 2.10]), as was having prior CVD (36.1 per 1,000-person years; ARI, 5.1% [95% CI, 4.9% to 5.2%]; RR, 2.16 [95% CI, 2.12 to 2.21]). Having both diabetes and CVD was associated with the highest risk of cardiovascular events (74.0 per 1,000 person-years; ARI, 12.0% [95% CI, 11.5% to 12.5%]; RR, 3.81 [95% CI, 3.69 to 3.93]). Similarly, in the 2014 cohort, having diabetes was associated with an increased risk of cardiovascular events (14.0 vs. 8.0 per 1,000 person-years; ARI, 2.0% [95% CI, 1.9% to 2.0%]; RR, 1.58 [95% CI, 1.56 to 1.61]), as was having prior CVD (23.9 per 1,000 person-years; ARI, 3.7% [95% CI, 3.6% to 3.9%]; RR, 2.06 [95% CI, 2.02 to 2.10]). Having both diabetes and CVD remained associated with the highest risk of cardiovascular events (51.3 per 1,000 person-years; ARI, 7.6% [95% CI, 7.3% to 7.8%]; RR, 3.10 [95% CI, 3.04 to 3.17]). Event rates decreased across categories from the 1994 cohort to the 2014 cohort (rate ratios, 0.49 for diabetes only, 0.66 for prior CVD only, 0.69 for diabetes and prior CVD, and 0.63 for neither diabetes nor CVD).

Limitations of the study include a lack of data on changes in certain risk factors (e.g., blood pressure), protective factors (e.g., statins), and cause-specific mortality, the authors noted. They added that changing surveillance practices may have affected diabetes misclassification rates. “These results suggest that diabetes is still an important cardiovascular risk factor but no longer equivalent to CVD—a change that likely reflects the use of modern, multifactorial approaches to diabetes,” the authors wrote.