CHICAGO, Jan. 2 (Xinhua) -- A sleepless night causes levels of the Alzheimer's protein amyloid beta to rise faster than the brain's waste-disposal system can remove it, a study of Washington University School of Medicine in St. Louis found.

Persistent high levels of the protein can set off a cascade of brain changes leading to dementia.

Researchers at the university studied eight people aged 30 to 60 with no sleep or cognitive problems. The participants were assigned randomly to one of three scenarios: having a normal night's sleep without any sleep aids; staying up all night; or sleeping after treatment with sodium oxybate, a prescription medication for sleep disorders.

Each scenario occurred during 36 hours of monitoring, starting in the morning and continuing through the afternoon of the following day. The researchers took samples of the fluid that surrounds the brain and spinal cord every two hours to monitor how amyloid beta levels change with time of day and tiredness.

All eight participants returned four to six months later to undertake a second scenario, and four people completed all three.

Amyloid beta levels in sleep-deprived people were 25 to 30 percent higher than in those who had slept the night through. After a sleepless night, amyloid beta levels were on par with the levels seen in people genetically predisposed to develop Alzheimer's at a young age.

"This study is the clearest demonstration in humans that sleep disruption leads to an increased risk of Alzheimer's disease through an amyloid beta mechanism," said senior author Randall Bateman, professor of neurology at Washington University in St. Louis.

One sleepless night probably has no effect on overall risk of Alzheimer's. Researchers are much more concerned about people with chronic sleep problems.

When amyloid beta levels in the brain are persistently high, the protein is more likely to start collecting into plaques. Such plaques damage nearby neurons and can trigger a cascade of destructive brain changes. The brains of people with Alzheimer's disease are dotted with such plaques.

In the study, people who took sleep medication had levels of amyloid beta no lower than people who had slept normally.

An estimated 50 million to 70 million American adults struggle to get a good night's sleep. Some have medical conditions such as sleep apnea.

Further studies are needed to determine whether improving sleep in people with sleep problems can reduce amyloid beta levels and risk of Alzheimer's disease.

The study has been published online in Annals of Neurology.