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.
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.
“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 conducted by 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 What causes 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 Ingredient found in red wine may slow 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 realise their sleep had been interrupted, and this went on for the entire night.
The participants’ spinal fluid were analysed 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 their sleep 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 Long daytime naps may increase risk of diabetes]
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.