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Stroke Health Center

'Silent' Stroke Doubles Risk of Dementia

Take Care of Your Blood Vessels to Avoid Losing Mental Function, Expert Says
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Although rare before age 30, the chance of having silent strokes doubles every 10 years, say researchers. By the time people reach their 70s, one in three has experienced at least one silent stroke per year -- usually showing no obvious initial symptoms and detectable only through a brain scan. But the injury accumulates over time, leading to symptoms of dementia such as memory and thinking impairments, as well as difficulty in walking.

In her study of 1,015 elderly patients, Breteler and her colleagues found that those who had silent strokes at the beginning of their study, as measured on an MRI, and who also showed no signs of dementia were more than twice as likely to demonstrate symptoms of mental decline over the course of the four-year study. Those with a history of silent strokes at the beginning of the study also had a faster rate of decline in their thinking and memory abilities compared with those who were stroke-free.

Their results are strikingly similar to a 1997 study, in which American researchers first suggested that silent strokes may increase the likelihood of later developing Alzheimer's. In reviewing autopsy reports and brain scans of deceased elderly nuns, they noted that Alzheimer's was found in nearly all of those with a history of silent strokes, compared with only 57% of stroke-free nuns.

What's more, one-third of the nuns whose brains showed definite signs of Alzheimer's hadn't exhibited any symptoms of the disease before their deaths. The reason: "They most likely had not suffered strokes," says that study's lead researcher, David Snowdon, PhD, MPH, of the Sanders-Brown Center on Aging at the University of Kentucky. Meanwhile, those with a history of silent strokes typically had the most severe Alzheimer's symptoms and a faster rate of functional decline.

"This study is really great news because there isn't any drug available today to slow down the lesions of Alzheimer's growing in your brain. But clearly, you can work on preventing stroke," Snowdon tells WebMD. "It's not rocket science that if you have one brain-damaging condition like stroke, another brain-damaging condition like Alzheimer's would add to your worries. Except in this case, it looks like the brain-damaging effects of stroke may actually trigger the Alzheimer's symptoms."

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