Covert ischemia - brain damage due to reduced blood flow without obvious clinical signs of stroke - is now known to be more common than clinically overt stroke, and has been associated with cognitive decline, dementia, depression, vascular Parkinsonism, gait impairment and falls. Reducing the prevalence of covert ischemia would likely result in substantial improvements in the health of older Canadians, and could possibly lead to major health savings in health costs for the care of the elderly. The prevalence, risk factors and consequences of covert ischemia in Canada are currently not known, but this information will be critically necessary for public policy decision-making and the planning of clinical trials for prevention strategies. We propose to address this limitation by carrying out an MRI study of covert ischemia in Canada, embedded within the ongoing PURE study.


Previous studies have demonstrated that covert ischemia is common in non-Canadian populations, and that the presence of one or more covert infarcts is associated with a 2 to 4-fold increased risk of subsequent dementia or clinically overt stroke. Similarly, persons with covert infarcts or large amounts of white matter lesions (WML) at baseline are at substantially higher risk of developing new covert infarcts or WML progression, which have been linked with declining cognitive performance. Overall, these data suggest that clinical or public health interventions to prevent new covert ischemia would reduce disability.

Previous studies suggest that age, hypertension and smoking are the strongest risk factors for covert infarction and WML, but other risk factors may also be present that are different from those of clinically overt stroke. For example, most of the variation in WML severity appears to be caused by genetic factors that remain to be discovered. Prior large population-based studies were predominantly conducted 10-15 years ago, and there is a need for additional studies to determine the prevalence of covert ischemia in the context of increasing rates of obesity and diabetes mellitus. More research is also needed in the area of dietary risk factors, as well as community and social determinants of covert ischemia.


1. To determine the prevalence of covert cerebral ischemia in community-dwelling people in urban and rural settings in Canada.

2. To determine the association between individual (including genetics), societal and environmental factors for development and progression of covert cerebral ischemia.

3. To determine the association between covert cerebral ischemia and cognitive function, mood and activities of daily living.


Five hundred PURE participants over the age of 40 were recruited for PURE Mind. Participants undergo a brain MRI and clinical testing to measure cognitive performance, mood, activities of daily living and gait. Detailed risk-factor data collected through the main PURE Study will be used alongside MRI and cognitive measures. Cognitive re-assessment takes place at 3 year intervals and a repeat MRI scan will take place 6 years after baseline.