While stroke is linked to both the development and worsening of cognitive impairment, researchers have long wondered: Is the reverse true as well? Yes, say the researchers whose new study appears in Canadian Medical Association Journal. People with some brain impairment, such as dementia, have a significant 39 percent increased risk of stroke compared to people with normal brain function. “Our findings suggest that identifying people with cognitive impairment may provide an even bigger opportunity to reduce the future burden of stroke through the timely implementation of evidence-based prevention strategies,” wrote the authors.

Stroke is the second leading cause of death worldwide and third in the United States; risk factors include blockage of blood vessels in the brain, hardening of the arteries, inflammation, and other vascular conditions. Stroke is a major contributor to disability, and in this regard stands right beside cognitive impairments, such as Alzheimer's disease. Interestingly, cerebrovascular disease and dementia share some common features, most notably a handful of risk factors. Obesity, hypertension, diabetes, high lipid (fat) levels, and physical inactivity play a role in both these disabling conditions.

To better understand the connections between stroke and dementia, a team of researchers in the U.S., Taiwan and South Korea conducted a review and analysis of cohort studies culled from published scientific literature. After sorting through about 7,500 possible studies, the researchers identified only 18 that had a 95 percent or greater estimate of reliability. These studies included, in total, 121,879 participants and 7,799 stroke events. Most had been conducted in North American or European countries, though one drew on participants in Taiwan, and three were international collaborations.

After analyzing the data, the researchers found cognitive impairment to be associated with a significantly higher risk of future stroke, especially ischemic and fatal stroke. In fact, among patients with dementia at baseline (the start of the study), the risk of future stroke was 39 percent higher than among those with normal brain function at baseline. Notably, this risk increased to 64 percent when a wider definition of cognitive impairment was used. “This association was consistent across diverse population subgroups,” the authors noted, having purposefully excluded those studies which might have incorporated selection bias.

"Given the projected substantial rise in the number of older people around the world, prevalence rates of cognitive impairment and stroke are expected to soar over the next several decades, especially in high-income countries," wrote the authors. Understanding how to prevent these two conditions, then, is key to maintaining health among aging citizens and also crucial to sustaining the more general public health.

Source: Lee M, Saver JL, Hong KS, et al. Cognitive impairment and risk of future stroke: a systematic review and meta-analysis. CMAJ. 2014.