The reciprocal risks of stroke and cognitive impairment in an elderly population.

Background: Stroke, dementia, and cognitive impairment no dementia (CIND) pose major threats to the elderly but have rarely been studied together in the same population. We aimed to compare the relative frequencies of stroke, CIND, and dementia in an elderly population and to examine whether cognitive impairment poses a risk for stroke.

Methods: Prevalences of stroke, CIND, and dementia were estimated among participants in the first clinical examination of the Canadian Study of Health and Aging (CSHA-1, n = 2,914). Incidence rates were determined at the 5-year follow-up (CSHA-2) among those cognitively normal and stroke free at CSHA-1 (n = 828). The associations between cognitive impairment and stroke were assessed by Cox regression analyses.

Results: Among elderly Canadians, the age-standardized prevalence of stroke, CIND, and dementia were 8%, 17%, and 8%, respectively. Alone or combined, they affected one fourth of the elderly. Among stroke survivors, 64% had cognitive impairment compared with 21% among stroke-free persons. Among the cognitively impaired, 25% had a stroke compared with 4% among the cognitively normal. The incidence rates of stroke, CIND, and dementia were 3, 6, and 3 per 100 person-years, respectively. Compared with cognitively normal subjects, the adjusted risk for incident stroke was 1.3 (95% confidence interval [CI], 0.9 to1.9) in patients with CIND and 2.3 (95% CI, 1.7 to 3.2) in patients with dementia regardless of whether "questionable stroke" was included.

Conclusions: Stroke and cognitive impairment pose risk for each other. CIND is highly prevalent, and some of its subtypes may represent treatable preludes to stroke and/or dementia.