According to researchers, from the University of Manchester, UK, spontaneous blood clots are significantly associated with both Alzheimer's disease and vascular dementia.
The researchers say this finding may hold the key to treating and preventing dementia.
It is estimated that Alzheimer's disease and vascular dementia represent four fifths of all dementias and to date the reason is unclear.
The researchers in this study monitored the occurrence of spontaneous cerebral emboli in 170 patients, half had Alzheimer's disease and the other half had vascular dementia along with a control group of 150 healthy people of the same age and sex ratio.
Patients on anticoagulant treatment, patients with severe dementia, and controls with marked cognitive impairment were excluded.
Spontaneous cerebral emboli, or spontaneous blood clots or debris from arterial disease in the brain was found after just one hour of monitoring, to be present in 40% of the Alzheimer's disease patients and 37% of the vascular dementia patients, compared with just 15% in the control group.
The researchers concluded that spontaneous cerebral emboli are closely linked to Alzheimer's disease and vascular dementia and may represent a potentially preventable or treatable cause of dementia.
They say that further research is needed as this study is the first of this type.