QUEBEC CITY — Among adult patients with congenital heart disease, type 2 diabetes can strike early and significantly affect mortality, according to a population-based cohort study presented at the 2025 Canadian Cardiovascular Congress. Unexpectedly, the risk was higher among women, even though patients with gestational diabetes were excluded from the analysis. The findings suggest a need to screen for diabetes earlier in patients with congenital heart disease.

“We know diabetes is a growing epidemic,” said Sabrina Maya D’Angelo, MD, second-year internal medicine resident at McGill University in Montreal, during her presentation of the data. “In 2011, [Jonathan Afilalo, MD, MSc, and colleagues] showed the comorbidities that affect mortality in the aging congenital heart disease population. Diabetes was one of these comorbidities, but this work was done in patients over 65 years of age…. We wanted to focus on the younger patients.”

D’Angelo and her colleagues had three objectives. “First, we wanted to calculate the incidence rate of type 2 diabetes mellitus in the congenital heart disease population and compare it to that of the general population,” she said. “We also wanted to compare the incidence rate of severe lesions to that of nonsevere lesions. Second, we wanted to identify the predictors of early-onset diabetes in adult congenital heart disease patients and then to assess the association between early-onset diabetes and all-cause mortality.”

The researchers conducted a population-based cohort study using the Quebec Congenital Heart Disease Database. They examined data from 1983 to 2017, which included socioeconomic status, hospitalizations, use of outpatient services, and vital status. Among a sample of 137,656 patients, 84,253 met the inclusion criterion of being aged 18 years or older and developing type 2 diabetes.

The investigators excluded patients with gestational diabetes and defined early-onset type 2 diabetes as disease occurring by age 40 or earlier. Incidence rates of type 2 diabetes were adjusted for competing risk for death, and propensity score matching was used to control for potential confounding variables when calculating survival following the development of type 2 diabetes.

Among the 84,235 patients who developed type 2 diabetes, 30,196 did so by age 40 years. The propensity-score matched analysis comprised 8825 pairs of patients: 2802 who developed diabetes by age 40 and 14,848 who developed it later in life.

The incidence of type 2 diabetes was higher in the congenital heart disease group vs the general Canadian population, patients aged 20-34 years (1.88 vs 1.40 per 1000 person-years, P < .001), patients aged 50-64 years (13.84 vs 11.08, P < .001), and patients aged 65-79 years (23.37 vs 15.14, P < .001) but not in patients aged 35-49 years (5.08 vs 5.40, P = .004). The incidence of diabetes in patients aged 20-34 years was higher among those with more severe congenital heart disease vs those with milder disease (2.47 vs 1.80 per 1000 person-years, P < .001).

Survival among individuals who developed type 2 diabetes by age 40 was lower than that among individuals who did not develop diabetes and those who developed diabetes later in life. Notably, the mortality hazard ratio (HR) was 2.5 times higher in patients with early-onset diabetes (HR, 4.19) than in those with those with late-onset disease (HR, 1.65).

Not surprisingly, predictors of developing early-onset type 2 diabetes included chronic liver and kidney disease, obesity, dyslipidemia, and hypertension. What was unexpected was that male sex was highly protective (HR, 0.69).

“What’s new and very interesting about the work that D’Angelo presented about diabetes is how big of an impact [it has] in…reproductive-age female patients with moderate-to-severe congenital heart disease,” Lily Lin, MD, pediatric cardiologist at the University of Alberta in Edmonton, told Medscape Medical News. Lin was not involved in the study but chaired the session in which it was presented.

“It was surprising because we always thought that being female protects against certain cardiovascular risks…. I really look forward to the next steps as she looks through a little bit more to see the granularities of the data, whether that can give us more clues. Or maybe we need to study it prospectively [to determine if we need to] be screening for diabetes earlier and [figure out] how we should better provide care, to minimize these additional risks for our patients.”

The study was funded by a Canadian Institute of Health Research Foundation grant. D’Angelo and Lin reported having no relevant financial relationships.