Significant decline in mortality related to diabetes from 1998 to 2014

1. In a large Swedish registry-cohort study, the authors report significant declines in all-cause mortality and diabetes-related complications in patients with both type 1 and 2 diabetes.

2. There was a similar decline in all-cause mortality between patients with type 1 diabetes and controls, whereas a greater decline in fatal outcomes was observed in controls compared to those with type 2 diabetes.

Evidence Rating Level: 2 (Good)

Study Rundown: In recent decades, improved understanding of type 1 and 2 diabetes has led to the adoption of evidence-based strategies for the prevention and treatment of diabetes as a form of cardiovascular risk reduction. Drawing on the Swedish National Diabetes Register, the study authors sought to investigate long-term trends in all-cause mortality and diabetes-related complications among diabetic patients versus non-diabetic matched controls in the Swedish population from 1998 to 2014. The authors report a significant decline in all-cause mortality and diabetes-related complications in patients with both type 1 and 2 diabetes. There was a similar decline in all-cause mortality between patients with type 1 diabetes and controls, whereas a greater decline in fatal outcomes was observed in controls compared to those with type 2 diabetes. In terms of nonfatal outcomes, including hospitalizations for myocardial infarction, coronary heart disease, and stroke, there were significant decreases in both diabetes groups compared to matched controls. Across all outcomes, there was a much higher rate of adverse outcomes, in absolute terms, in the diabetic groups compared to controls.

This study leverages the powerful Swedish diabetes registry in a matched-cohort design to show substantial improvements in mortality and cardiovascular complications among type 1 and 2 diabetic patients. Interestingly, they report a decline in heart failure related complications among patients with type 2 diabetics compared to controls, but not among type 1 diabetic patients. As with all registry studies, potential limitations include the possibility of misclassification bias and unaccounted secular trends.

Click to read the study, published today in NEJM

Relevant Reading: Projection of the year 2050 burden of diabetes in the US adult population

In-Depth [retrospective cohort]: This study involved 36 869 patients with type 1 diabetes and 457 473 patients with type 2 diabetes drawn from the Swedish National Diabetes Register, matched (by age, sex, and county) with controls from the general Swedish population. Patients with type 1 diabetes were on average 35 years of age; those with type 2 diabetes were on average 65.2 years of age at study entry. There was a median of 15 years of observation in the cohort. In terms of all-cause mortality, the absolute changes were -31.4 and -69.6 deaths per 10,000 person-years in the type 1 and type 2 diabetes cohorts, respectively. The hazard ratio comparing all-cause mortality in patients with type 1 diabetes compared to controls was 1.08 (95%CI 0.99 to 1.18; p = 0.09). The corresponding hazard ratio for controls compared to patients with type 2 diabetes was 0.87 (95%CI 0.85 to 0.89; p < 0.001). In terms of hospitalization for cardiovascular disease, there were event rate reductions of 36% and 44% among patients with type 1 and 2 diabetes, respectively; these rates were significantly higher than those found among matched controls, a finding that was consistent for hospitalizations related to myocardial infarction, coronary heart disease, and stroke. There was no significant difference in the rate of hospitalization for heart failure in patients with type 1 diabetes compared to controls; there was a 29% reduction in hospitalization for heart failure in patients with type 2 diabetes compared to controls (HR 0.71; 95%CI 0.69 to 0.73).

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