Long-term population-based trends in the incidence of cardiovascular disease in individuals with type 1 diabetes from Finland: a retrospective, nationwide, cohort study.

BACKGROUND

Cardiovascular disease is the main determinant of premature mortality in patients with type 1 diabetes. However, time trends regarding different types of cardiovascular disease in childhood-onset type 1 diabetes with a long timespan from the diagnosis of diabetes are not well established. This study aimed to investigate the cumulative incidence of cardiovascular disease in individuals with type 1 diabetes in a population-based cohort in Finland, the country with the world's highest incidence of type 1 diabetes.

METHODS

In this retrospective, nationwide registry-based, cohort study, all patients who were diagnosed between Jan 1, 1965, and Dec 31, 1999 with type 1 diabetes when they were younger than 15 years old in Finland were followed up and monitored for the occurrence of cardiovascular disease (including coronary artery disease, stroke, peripheral artery disease, and heart failure) until the end of 2016 and for cardiovascular disease mortality until 2017. Cumulative incidences of cardiovascular disease were calculated by the Fine and Gray method according to the year of diabetes diagnosis using six diagnosis cohorts: 1965-69, 1970-74, 1975-1979, 1980-84, 1985-89, 1990-94, and 1990-95. Trends in cardiovascular disease event rates were analysed by Fine and Gray competing risks regression models using year of diabetes diagnosis as continuous variable. In addition, non-linearity in trends was assessed with restricted cubic splines. The excess risk of coronary artery disease and stroke was estimated by comparison with the risk in the Finnish general population by calculating standardised incidence ratios (SIRs) and their time trends. The data for Finnish general population were drawn from the Cardiovascular Disease Register of the National Institute of Health and Welfare. The SIRs were calculated as ratios of observed and expected number of events in individuals with type 1 diabetes during 1991-2014.

FINDINGS

11 766 individuals were included in this study. During 361 033 person-years of follow-up and a median of 29·6 years (IQR 22·3-37·9) follow-up, a total of 1761 individuals had single or multiple types of cardiovascular disease events. 2686 events (864 [32·2%] coronary artery disease events, of which 663 were acute myocardial infarctions; 497 [18·5%] strokes; 854 [31·8%] peripheral artery diseases, of which 498 were lower extremity amputations; and 471 [17·5%] heart failure events) were reported until Dec 31, 2016, and 1467 deaths until Dec 31, 2017. Cardiovascular disease risk decreased linearly by 3·8% (hazard ratio [HR] 0·96 [95% CI 0·96-0·97]; p<0·0001) by later calendar year of diabetes diagnosis (p<0·0001). There was a decrease in the SIRs for both coronary artery disease and stroke within all 10-year age groups under 65 years, except for stroke in the oldest age group. However, the SIR was still 8·9 (95% CI 3·9-17·5) for coronary artery disease and 2·9 (1·3-5·7) for stroke in those diagnosed with type 1 diabetes in the 1990s. Finally, the cardiovascular disease death rate decreased constantly by diagnosis year.

INTERPRETATION

The risk of cardiovascular disease has decreased over time in Finland in individuals with childhood-onset type 1 diabetes. However, there is still considerable excess cardiovascular disease risk in individuals with type 1 diabetes compared with the general population. These results highlight the need for studies on the mechanisms of atherosclerosis from the time of diagnosis of type 1 diabetes to facilitate early and effective prevention of cardiovascular disease in these individuals.

FUNDING

Folkhälsan Research Foundation, Academy of Finland, Wilhelm and Else Stockmann Foundation, Liv och Hälsa Society, Novo Nordisk Foundation, Finnish Foundation for Cardiovascular Research, Finnish Diabetes Research Foundation, Diabetes Research Foundation, Medical Society of Finland, Sigrid Jusélius Foundation, and Helsinki University Hospital Research Funds.