A 50-year-old with Type 2 diabetes will lose an average of six years of life as a result of the disease, only one less than would be lost by a long-term smoker of the same age, researchers reported Wednesday.
He or she is more than twice as likely to die of cardiovascular disease as someone without diabetes and 25% more likely to die of cancer, according to the report, an international study of more than 820,000 people published in the New England Journal of Medicine.
People with Type 2 diabetes are also more likely to die from kidney disease, liver disease, pneumonia, infectious diseases and even intentional self-harm, according to the study, which was conducted by the Emerging Risk Factors Collaboration, based at the University of Cambridge in England.
The data are especially concerning in light of the rapidly expanding incidence of diabetes in the United States, fueled by the rise in obesity. An estimated 25.8 million Americans have diabetes, 10 million more than two decades ago.
Researchers knew that diabetes could shorten lifespan, "but this really says how many years of life may be lost and to what causes," said Dr. David M. Kendall, chief scientific and medical officer of the American Diabetes Assn., who was not involved in the study.
The report also shows that those who have pre-diabetes — in which blood glucose levels are higher than normal, but not high enough to be classified as diabetic — are at risk for many of the same causes of death, he noted. An estimated 79 million Americans have pre-diabetes.
"Diabetes is often seen as a condition rather than an illness, something you can live with," Kendall said. "Well, in fact, this shows that it is associated with a significant risk of both morbidity and mortality."
The Emerging Risk Factors Collaboration is an international group of researchers that has previously studied the association of cholesterol, lipids and inflammation-promoting proteins in the blood with cardiovascular disease and other causes of death. In 2009, the group decided to extend its research to diabetes, focusing on 97 large studies that tracked subjects for an average of 13.5 years and had adequate information about fasting blood-glucose levels and the diagnosis of diabetes and other medical conditions. None of the subjects had cardiovascular or other diseases at the beginning of the studies.
The group reported that Type 2 diabetics were 2.32 times as likely as non-diabetics to die from cardiovascular disease during the course of a study and 25% more likely to die from cancer. Diabetes was moderately associated with increased risk of death from cancers of the liver, pancreas, ovary, colon, rectum, lung, bladder and breast. Diabetics were, however, less likely to die from prostate cancer.
Those findings are in general agreement with a recent statement issued jointly by the American Diabetes Assn. and the American Cancer Society. That document noted that it was unclear whether the cancers were caused directly by diabetics' high blood glucose levels or whether diabetes and cancer both result from underlying biological factors such as overproduction of insulin or an inability to properly respond to insulin.
That document also noted that there was not enough evidence about whether Type 1 diabetes, in which the pancreas fails to produce enough insulin, is linked to an increased risk of cancer.
All of the subjects in the 97 studies were diagnosed with diabetes and began receiving medication to treat their condition, but the researchers were not able to determine whether the patients were able to bring it under control.
"Eventually, we would like to be able to be at the point where we can say what would happen if the diabetes is brought under control," but researchers are nowhere near that yet, said Dr. J. Leonard Lichtenfeld, deputy chief medical officer of the American Cancer Society.
According to the new research, Type 2 diabetics are also about three times as likely to die of kidney disease, 2.4 times as likely to die of pneumonia or other infections, 2.3 times as likely to die of liver disease, 70% more likely to die of falls, 64% more likely to die of mental disorders, 58% more likely to die of intentional self-harm and 27% more likely to die of chronic obstructive pulmonary disease.
"It's surprising that everything under the sun was associated with diabetes," said Dr. Spyros Mezitis, an endocrinologist at Lenox Hill Hospital in New York, who was not involved in the research. It is clear why there is a link between diabetes and cardiovascular disease, he said, "but when it comes to nonvascular disease, it's a little more difficult to understand why there is an association."
For some of the causes of death, reduced immune function and impaired defense systems are clearly playing a role, he added. But for others, he said, "more studies are needed to somehow make these associations plausible."