MANCHESTER (BBC Health News) -- Blood clots in the brain may be a sign of increased risk of developing dementia, scientists suggest.

The clots, known as cerebral emboli, were seen in people who had Alzheimer's disease or another form of dementia.

The University of Manchester team who carried out the study say they could act as an early warning sign of the conditions.

Dementia experts said the British Medical Journal finding was a significant and valuable discovery.

The researchers monitored the occurrence of spontaneous blood clots in the brain in 170 patients -- 85 with Alzheimer's disease and 85 with vascular dementia -- compared them with groups of people of the same age.

Forty per cent (32) patients with Alzheimer's and 37% (31) with vascular dementia had clots in just one hour of monitoring, compared to just 14 and 15% in the healthy groups (12 patients in each). -------------------Detection

The researchers, led by Professor Charles McCollum, said the finding suggested that the types of dementia have more in common than had been previously thought.

They said more research was needed to investigate their finding further.

Clive Ballard, director of research at the Alzheimer's Society which partially funded the study, said: "Blood clots in the brain can be detected in people at any age and their prevalence in people with Alzheimer's disease is a very significant finding. "The strong correlation between Alzheimer's and blood clots could lead to a way of detecting and treating Alzheimer's disease much earlier."

He added: "It is also significant that the blood clots were present in people with vascular dementia and Alzheimer's. "This is an important link between the two as it could be a valuable scientific discovery, creating a new and important target for treatment.”