A British study warns that blood clots to originate in the heart and wander to the brain could cause dementia. The researchers found these clots in the brains of 40% of 85 people with Alzheimer's and 37% of people with vascular dementia, according to the report published on April 28.

The clots "may represent a potentially reversible or treatable cause of dementia," the researchers mentioned. Clots, a known cause of stroke, form in the circulatory systems of people with an abnormal heart rhythm.

Both Alzheimer's and vascular dementia are associated with vascular risk factors such as smoking, hypertension, high cholesterol, and diabetes, as well as carotid atherosclerosis, the authors noted.

During a single hour of testing, doctors found that clots occurred in 40% of the patients with Alzheimer's disease and in 37% of those with vascular dementia.

"This is another indication that Alzheimer's disease probably is not just one disease," said Dr. Julie A. Schneider, an associate professor of neurology and neuropathology at the Rush Alzheimer's Disease Center in Chicago. "There are probably multiple things happening in the brains of older people, and some of them are vascular."

"As expected, spontaneous blood clots were associated with all the major cardiovascular risk factors in," the investigators wrote. "We found no such association in dementia patients, implying that blood clots may be universal in dementia."