They also found that after several nights of sleep disruption another chemical began to rise. Called tau, it is known to cause tangles in the brain and is also linked to Alzheimer’s disease.

“We showed that poor sleep is associated with higher levels of two Alzheimer’s-associated proteins,” said Professor David Holtzman, head Department of Neurology at Washington Medical School.

“We think that perhaps chronic poor sleep during middle age may increase the risk of Alzheimer’s later in life.”

Around 800,000 people are currently living with dementia in Britain, and the majority have Alzheimer’s disease, for which there is no cure. Although the incidence of dementia is dropping as people adopt healthier lifestyles, the number of people living with the illness is expected to rise to 1.2 million by 2040 because of the ageing population.

More than a third of Britons also sleep for less than six hours a night, according to The Sleep Council.

Previous studies have shown that poor sleep increases the risk of cognitive problems. People with sleep apnea, for example, a condition in which people repeatedly stop breathing at night, are at risk for developing mild cognitive impairment an average of 10 years earlier than people without the sleep disorder. Mild cognitive impairment is an early warning sign for Alzheimer’s disease.

The researchers studied 17 healthy adults aged 35 to 65 with no sleep or cognitive problems. Each participant wore an activity monitor on the wrist for two weeks to measure how much time they slept at night. They were then monitored overnight in a sleep lab where they had their rest regularly disrupted by loud beeps.

After the experiment each underwent a spinal tap so the researchers could measure the levels of amyloid beta and tau in the fluid surrounding the brain and spinal cord.

The researchers compared each participant’s amyloid beta and tau levels after the disrupted night to the levels after the uninterrupted night, and found a 10 percent increase in amyloid beta levels after a single night of interrupted sleep.

Participants whose activity monitors showed they had slept poorly at home for the week before the spinal tap also showed a spike in levels of tau.

“The main concern is people who have chronic sleep problems,” said Professor Yo-El Ju, of Washington University.

“I think that may lead to chronically elevated amyloid levels, which animal studies have shown lead to increased risk of amyloid plaques and Alzheimer’s.”

Dr Laura Phipps of Alzheimer’s Research UK, said: “There is mounting evidence of a link between poor quality sleep and Alzheimer’s disease, but it is difficult to tease apart cause and effect in this relationship and determine whether sleep problems might cause Alzheimer’s brain changes or vice-versa.

“The development of Alzheimer’s is a process that takes many years and is likely to depend on multiple genetic, health and lifestyle factors.”

Pof Ju emphasized that her study was not designed to determine whether sleeping more or sleeping better reduce risk of Alzheimer’s but, she said, neither can hurt.

“Many, many people are chronically sleep-deprived, and it negatively affects their health in many ways,” she added.

“At this point, we can’t say whether improving sleep will reduce your risk of developing Alzheimer’s. All we can really say is that bad sleep increases levels of some proteins that are associated with Alzheimer’s disease. But a good night’s sleep is something you want to be striving for anyway.”

Source: Brain.