Scientists have shown that just one night of interrupted sleep causes an increase in brain proteins associated with Alzheimer's disease.
The findings could answer the long-standing question of how disrupted sleep could be linked to Alzheimer's and help protect those who suffer from chronic sleep deprivation – it comes down to the protective function of slow-wave sleep.
"We showed that poor sleep is associated with higher levels of two Alzheimer's-associated proteins," said one of the researchers, David M Holtzman, from Washington University.
"We think that perhaps chronic poor sleep during middle age may increase the risk of Alzheimer's later in life."
Alzheimer's is a disease characterised by a gradual cognitive decline and memory loss that affects more than five million Americans. The death rate from Alzheimer's has increased 55 percent over the past 15 years.
This new research sheds some light on these questions.
The team found that just one night of tossing and turning caused an increase of amyloid beta in the brain and if you are unfortunate enough to have had a full week's worth of bad sleep there is also an increase in the protein tau.
"We were not surprised to find that tau levels didn't budge after just one night of disrupted sleep while amyloid levels did, because amyloid levels normally change more quickly than tau levels," said Yo-El Ju, another researcher on the team, also from Washington University.
"But we could see, when the participants had several bad nights in a row at home that their tau levels had risen."
The scientists took 17 healthy adults, between the ages of 35 and 65, who had no history of sleep problems. They fitted them with an activity monitor to keep a record of how much they'd slept in the previous two weeks.
Although the activity monitor provided valuable information, the most interesting data came from the sleep laboratory.
The sleep lab is a dark room that contains a good bed, is soundproof and climate controlled. The participants were fitted with electrodes on their scalp, to monitor brain activity, and headphones to allow the scientists to subtly control their sleep patterns.
During the study, half of the participants were assigned to have their sleep interrupted while bunking at the sleep lab.
Every time they entered a sleeping stage with slow-wave patterns (characteristic of a deep restful and dreamless sleep) a series of beeps were sent through the headphones until the brainwaves increased in activity.
The next morning, the participants who had had their sleep interrupted said they were tired and felt unrefreshed. Interestingly, they didn't often remember being awakened by the noise in the headphones.
At this point, the sleep chamber became a little more gruesome than relaxing.
To measure the levels of amyloid beta and tau in the cerebral fluid after the night of sleep, needles were pushed into the participant's spinal cords and samples of spinal fluid was taken.
The researchers found that there was a ten percent increase in amyloid beta in those who had been disrupted during slow-wave sleep for one night.
It wasn't until the team looked at the activity monitors of the previous two weeks that a connection between the presence of the protein tau and longer periods of sleep deprivation was made.
But there's some good news hidden in the results for restless sleepers.
The scientists aren't convinced that one night of sleep poses a significant risk in developing Alzheimer's. It's likely that the negative effects are reversed once you return to sleeping normally.
Once you are able to get a good amount of slow-wave sleep it removes the build-up of by-products from the cerebral fluid.
The problem lies with those experiencing more serious sleeping problems.
"The main concern is people who have chronic sleep problems," said Ju. "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."
Ju said that the study can't determine for certain if better quality sleep reduces the risk of Alzheimer's disease but it certainly wouldn't hurt.
"Many, many Americans are chronically sleep-deprived, and it negatively affects their health in many ways," said Ju.
"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."
We'll happily take that advice on board and tuck ourselves in for a good night's sleep.
The study has been published in the journal Brain.