People who regularly have disturbed sleep may be at a greater risk of Alzheimer's disease, research shows.

Scientists at Washington University School of Medicine in St Louis, who carried out a two-week sleep study, found an increased likelihood of finding amyloid plaques in a person's brain if they have poor sleep.

An amyloid plaque is a tangle of certain proteins in the brain and is commonly a hallmark of Alzheimer's disease. One protein that can be found in these is called amyloid beta, which is considered to be a major cause of nerve cell death.

Of the 100 people observed in the study, who ranged in age from 45 to 80, those who woke up more than five times an hour showed greater evidence of the presence of amyloid build-up in their brains.

Those whose sleep efficiency, calculated by dividing the amount of time asleep by the time spent in bed, was less than 85 percent were considered at a greater risk of preclinical Alzheimer's disease.

"This interesting study supports previous research that suggests regularly disrupted sleep could be linked to plaques known to develop in Alzheimer's disease," a spokesman for the Alzheimer's Society said.

"Much more research is needed, as we don't know whether these changes in people's sleep patterns over longer periods may increase chances of cognitive decline and dementia.

"Those of us who may have to count sheep at times should not panic. The best way to reduce your risk of dementia is to eat healthily, take regular exercise, don't smoke and get your blood pressure and cholesterol checked."

The research findings will be presented at the American Academy of Neurology's 64th annual meeting in New Orleans in April.