Background and Purpose—Several studies indicate that stroke increases the risk of dementia. Most of these studies lacked the ability to take accurately assessed prestroke cognitive function into account. Whether the effects of stroke merely unravel an ongoing underlying dementing process or in fact cause the dementia has implications for the prevention of dementia in persons with cerebrovascular disease. We explored in a prospective cohort study whether stroke occurrence was related to a higher risk of subsequent dementia and whether this association was dependent on prestroke slope of cognitive function.

Methods—Cox proportional hazard models were used to relate incident stroke as a time-varying exposure with the risk of dementia in 6724 participants of the Rotterdam Study without dementia or stroke at baseline (49 361 person years of follow-up). Subsequently Cox proportional hazard models were performed to assess whether this association was dependent on slope of prestroke cognitive performance and other risk factors for cognitive decline.

Results—Independent of both level and the rate of change of prestroke cognitive performance and other risk factors for cognitive decline, incident stroke was associated with a more than doubled risk of subsequent dementia (hazard ratio, 2.1; 95% CI, 1.55 to 2.81).

Conclusions—Prestroke cognitive function is not a major determinant of the effect of stroke on the risk of poststroke dementia.