The substantially increased risk of premature death associated with type 2 diabetes is primarily confined to those individuals who also have kidney disease, new research shows. And the chief cause of this excess mortality was cardiovascular in nature, Maryam Afkarian, MD, from the University of Washington, Seattle, and colleagues report in a study published online in the Journal of the American Society of Nephrology.
Dr. Afkarian said it was "surprising that kidney disease was such a prominent marker of dying early in type 2 diabetes. And we know from prior research that the more severe the kidney disease, the greater the risk, so we should focus on preventing kidney disease from developing in diabetics, and if they do develop it, we should try to slow it down," she told Medscape Medical News. "This population — with type 2 diabetes and kidney disease — is one we really need to focus on for modifying risk factors and controlling their diabetes. This could be where the big bucks are, the big pay in managing diabetes," she added. She noted also that "when you take kidney disease out, mortality is not much higher among type 2 diabetics than it is in the general population," something she says has not really been appreciated before.
Attempt to Better Define Why Diabetics Die Younger
Describing the observational study she and her colleagues conducted, Dr. Afkarian said: "Diabetes is known to be a risk factor for premature death; diabetics generally die younger, and we were attempting to better define that."
They examined 10-year mortality by diabetes and kidney-disease status for 15046 participants in the third US National Health and Nutrition Examination Survey (NHANES III) by linking baseline data with the National Death Index. Kidney disease — defined as a urinary albumin/creatinine ratio of 30 mg/g or less and/or an estimated glomerular filtration rate (GFR) 60 mL/min per 1.73 m2 or less — was present in 42.3% and 9.4% of individuals with and without type 2 diabetes, respectively.
Among those without kidney disease or diabetes (reference group), 10-year cumulative all-cause mortality was 7.7%, compared with 11.5% among individuals with type 2 diabetes but no kidney disease and 31.1% in those with diabetes and kidney disease. This represented an absolute risk difference with the reference group of 3.4% among those with diabetes (adjusted for demographics, smoking, blood pressure, and cholesterol) and 23.4% among those with type 2 diabetes and kidney disease (similarly adjusted). The fact that the risk differences were evaluated on an absolute scale is particularly relevant to clinical care and public health, Dr. Afkarian and colleagues say.
"The presence of kidney disease robustly identifies a diabetes subpopulation at high risk of death," they observe. "One of the major ways that kidney disease contributes to increased mortality is that it makes cardiovascular disease worse," Dr. Afkarian added.
And expanding upon the finding that mortality was not much higher in those with type 2 diabetes than in the general population, she remarked, "This has been seen before in type 1 diabetes, but type 2 is so different, and by the time you get it, you generally have high blood pressure, high cholesterol etc, so it was surprising."
The authors have disclosed no relevant financial relationships.
J Am Soc Nephrol. Published online January 24, 2013.