Duration of diabetes and risk of ischemic stroke: The Northern Manhattan Study

Background and Purpose-Diabetes increases stroke risk, but whether diabetes status immediately before stroke improves prediction and whether duration is important are less clear. We hypothesized that diabetes duration independently predicts ischemic stroke. Methods-Among 3298 stroke-free participants in the Northern Manhattan Study, baseline diabetes and age at diagnosis were determined. Incident diabetes was assessed annually (median, 9 years). Cox proportional hazard models were used to estimate hazard ratios (HR) and 95% CI for incident ischemic stroke using baseline diabetes, diabetes as a time-dependent covariate, and duration of diabetes as a time-varying covariate; models were adjusted for demographic and cardiovascular risk factors. Results-Mean age was 69±10 years (52% Hispanic, 21% white, and 24% black); 22% had diabetes at baseline and 10% had development of diabetes. There were 244 ischemic strokes, and both baseline diabetes (HR, 2.5; 95% CI, 1.9-3.3) and diabetes considered as a time-dependent covariate (HR, 2.4; 95% CI, 1.8-3.2) were similarly associated with stroke risk. Duration of diabetes was associated with ischemic stroke (adjusted HR, 1.03 per year with diabetes; 95% CI, 1.02-1.04). Compared to nondiabetic participants, those with diabetes for 0 to 5 years (adjusted HR, 1.7; 95% CI, 1.1-2.7), 5 to 10 years (adjusted HR, 1.8; 95% CI, 1.1-3.0), and 10 years (adjusted HR, 3.2; 95% CI, 2.4-4.5) were at increased risk. Conclusions-Duration of diabetes is independently associated with ischemic stroke risk adjusting for risk factors. The risk increases 3% each year, and triples with diabetes 10 years.