What has been less clear is whether that risk peaks with the onset of the disease or if it gradually increases over time.
"This study solidifies the idea that duration is also an important factor, beyond sort of the ‘yes or no' of having diabetes," says Ken Uchino, a stroke neurologist at Cleveland Clinic in Ohio.
"Over time, diabetes, probably through elevated blood sugar, injures the arteries. And [blockages] probably develop over time at a higher or more rapid rate in people who have diabetes," says Uchino, who reviewed the study for WebMD, but was not involved in the research.
Tracking Diabetes and Stroke
The study followed nearly 3,300 seniors who lived in an ethnically diverse part of New York City. None had ever had a stroke.
About 22% of the people had diabetes at the start of the study and another 10% developed diabetes during the study. Over an average follow-up period of nine years, there were 244 reported strokes.
The study confirms that the risk of stroke is elevated in people with diabetes. It also shows that when compared to people who don't have diabetes, the risk of stroke increases significantly every year a person lives with the disease. After 10 years of diabetes, the researchers report that stroke risk triples.
Those risks remained even after researchers accounted for other factors known to influence stroke risk, including age, smoking, physical activity, a history of heart disease, high blood pressure, and cholesterol.
"We were able to establish that the risk is really pretty robust after about 10 years," says researcher Mitchell S.V. Elkind, MD, MS, associate chairman of neurology and epidemiology at Columbia University Medical Center in New York City.
As rates of obesity and physical inactivity rise, Elkind says, "We're going to see people who develop diabetes at earlier ages and who will therefore have it for many years, and we expect that's going to have a big impact on the number of strokes that occur."
Advice to Patients
Elkind says the study also underscores the importance of diabetes prevention, through a healthy diet and regular exercise.
For people who already have the disease, he says, other research has shown that controlling other things that are bad for the heart, such as high blood pressure and high cholesterol, can also help to lower some of the risk.
The research is published in the American Heart Association journal Stroke.
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