The longer you have diabetes, the higher your risk for stroke, according to a study published on- line Thursday in Stroke, an American Heart Association journal. As part of the Northern Manhattan Study, researchers from Columbia University Medical Center followed 3,298 people (average age 69) who had never had a stroke. Nearly 22 percent of participants had type 2 diabetes at the start of the study. After an average nine years of follow-up, an additional 10 percent developed diabetes. After considering other factors such as age, smoking history, physical activity, history of heart disease, blood pressure and cholesterol, researchers said that compared to people without diabetes, the risk of stroke increased: 70 percent in people with diabetes for less than five years; 80 percent in people with diabetes for five to 10 years; three-fold in people with diabetes for 10 years or more. \"The findings emphasize the chronic nature of diabetes and the fact that it damages the blood vessels over time,\" said Mitchell Elkind, the study\'s senior author and associate chairman of Columbia University Medical Center. Some of the reasons for increased stroke risk may include an association between longer diabetes duration and thicker plaque in neck arteries and the higher prevalence of hypertension, accelerated vascular complications and clotting abnormalities in diabetics, the researchers said. According to the American Diabetes Association, there are nearly 26 million Americans with diabetes.