Stroke Increases the Risk of All-Cause Dementia

Stroke is a strong independent risk factor for all-cause dementia, according to research published online ahead of print August 25 in Alzheimer’s & Dementia. Clinicians should incorporate stroke-prevention strategies into their health interventions to reduce patients’ risk of dementia, said the authors.

“Around a third of dementia cases are thought to be potentially preventable, though this estimate does not take into account the risk associated with stroke,” said David Llewellyn, PhD, Senior Research Fellow at University of Exeter Medical School in the United Kingdom. “Our findings indicate that this figure could be even higher and reinforce the importance of protecting the blood supply to the brain when attempting to reduce the global burden of dementia.”

David Llewellyn, PhD

Meta-Analysis of Previous Research

Stroke is a recognized risk factor for all-cause dementia, but no researchers had previously performed a meta-analysis to quantify the risk. Dr. Llewellyn and colleagues searched Medline, PsycINFO, and Embase databases for prospective studies that investigated the association between prevalent or incident stroke and incident all-cause dementia. They excluded studies that lacked a comparison group or that had a comparison group other than a stroke-free group. The investigators pooled adjusted estimates across studies using random effects meta-analysis and evaluated potential effect modifiers with meta-regression.

Dr. Llewellyn and colleagues identified 11,129 articles, 26 of which were eligible for analysis. They also included 16 studies from a previous systematic review and four studies identified through backward and forward citation searches. In all, 36 studies examined prevalent stroke (1.9 million participants), and 12 studies examined incident stroke (1.3 million participants). The studies were conducted in America, Europe, Asia, and Australia and included more than three million participants. Follow-up periods ranged from nine months to 25 years.

Stroke Affected Dementia Risk

When the researchers pooled results from 22 cohorts of participants who were cognitively normal at baseline, they found that those with prevalent stroke had a higher adjusted risk of incident dementia, compared with those without stroke (hazard ratio [HR], 1.69). Sensitivity analyses did not change the results significantly. Prevalent stroke was associated with a higher risk of incident dementia among men than among women. Sex explained 50.2% of heterogeneity between studies for prevalent stroke.

After combining the adjusted results from eight studies, Dr. Llewellyn and colleagues found that incident stroke more than doubled the risk of incident all-cause dementia, compared with no incident stroke (risk ratio [RR], 2.18). For a sensitivity analysis, the investigators excluded three studies that combined stroke with transient ischemic attack; this adjustment strengthened the association.

The study’s strengths include the investigators’ search of several major databases and their contacts with authors who provided relevant data. The analysis reflects the limitations of the original studies, however. These limitations include selective samples and differences in stroke assessment and dementia diagnosis criteria. In addition, dementia may develop years before it is diagnosed. “More detailed reporting of the interval between stroke occurrence and dementia diagnosis in future studies will help to better characterize the role of time since stroke in the risk of dementia,” said Dr. Llewellyn.

—Erik Greb

Suggested Reading

Kuz´ma E, Lourida I, Moore SF, et al. Stroke and dementia risk: a systematic review and meta-analysis. Alzheimers Dement. 2018 Aug 25 [Epub ahead of print].