A single night of poor sleep can cause a spike in brain proteins linked to Alzheimer’s disease, a new study reports.
Researchers from the U.S. and the Netherlands have found
that sleep helps the body clear away two compounds in the brain, called amyloid
and tau, and interrupted, poor sleep may cause too much of them to build up.
While the study doesn't show that poor sleep causes
Alzheimer's, it adds one more piece to the puzzle of what causes dementia.
[Read more Study:Access to nature makes men and seniors sleep better]
The team believes that the findings back the notion that
chronic poor sleep in midlife could elevate the risk of developing Alzheimer's
later in life.
Read more Does
Memory Loss Always Mean Dementia?
“When people had their slow-wave sleep disrupted, their
amyloid levels increased by about 10 percent,” says study leader Dr. Yo-El Ju
of Washington University in St. Louis.
Although scientists knew there was a connection between
dementia and poor sleep, it wasn’t clear whether dementia was driving insomnia
or vice versa.
The study was jointly conductedby researchers from Washington University School of Medicine in St.
Louis; Stanford University in California, in the U.S., and Radboud University
Medical Centre in the Netherlands.
Alzheimer’s
disease is a neurodegenerative disease that progresses rapidly. It is the
most common cause of dementia, accounting for about 70% of all dementia cases.
The disease affects memory, decision-making, language, thinking, and speech.
The brains of people
with Alzheimer's disease feature two hallmarks of the disease – plaques of
amyloid protein and tangles of tau protein. These plaques and tangles causes
neuron cells to die.
In the UK, around 850,000 people are currently living with
dementia, and the majority have Alzheimer’s disease, for which there is no
cure. Although the number of dementia cases 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. [Read more Whatcauses aging? Can the process be slowed?]
More than a third of Britons also sleep for less than 6
hours a night, according to The Sleep Council.
For their study, the researchers sought to identify the most
important phase of sleep.
“What we did was allow people to sleep a normal amount of
time, but we prevented them from getting deep sleep or what is called slow-wave
sleep,” Ju told NBC News.
“When we interrupted just the slow-wave sleep part, they
still had an increase in amyloid. So this tells us it's getting the deep
slow-wave sleep that's important for reducing the levels of amyloid.”
Ju and colleagues recruited 22 healthy adults aged between
35 and 65. All the participants reported experiencing no sleep problems and had
no cognitive impairments.
The participants showed up in a controlled sleep lab. Half
were allowed to sleep normally, while the other half were constantly kept in
shallow sleep. [Read more Newprotein target may reverse memory loss in Alzheimer’s]
“As soon as they got into slow-wave sleep, they got a beep.
And the beeps got louder and louder and louder until they came out of the deep
sleep,” says Prof. Ju.
“It was pretty harsh.”
The participants didn’t realize their sleep had been
interrupted, and this went on for the entire night.
The participants’ spinal fluid was analyzed in the morning.
“When people had their slow wave sleep disrupted, their
amyloid levels increased by about 10 percent,” Prof. Ju says.
The subjects were also fitted with sleep monitors to measure
theirsleep at home. Participants who experienced poor sleep at home were found
to have higher levels of a second Alzheimer’s related protein called tau. [Read
more Scientistsreport significant breakthrough in anti-aging]
Prof. Ju says they were not surprised to see that tau levels
didn’t increase after only one night of poor sleep whereas this did cause
amyloid levels to rise, since tau levels tend to change more slowly.
“But we could see, when the participants had several bad
nights in a row at home that their tau levels had risen,” she adds.
Prof. Ju concludes by saying:
“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.”
Next, the team plans to study whether treating obstructive sleep
apnea will improve people's slow-wave sleep and affect amyloid levels. Sleep
apnea is a common cause of sleep disruption. People with this condition have a
higher risk of developing dementia.
The study was published in the journal Brain.
