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Poor sleep can indicate that people at are risk of developing Alzheimer's disease. Istock

People who have trouble sleeping may be more likely to develop Alzheimer's disease in later life than those who do not, a study has shown. Scientists have established a link between poor sleep and some biological markers for the neurological disease.

The world population is ageing and with up to 50 million people already suffering from dementia globally, delaying or preventing the development of the disease is a major public health priority. Part of it involves identifying risk factors that can be modified.

Several studies have already identified an association between poor sleep and a build-up of harmful proteins known as amyloid plaques in the brain.

Amyloid plaques and tau tangles (another type of protein) are a hallmark of Alzheimer's, but other biomarkers in the body can indicate that a person is at risk of developing the disease.

In a study now published in the journal Neurology, scientists investigated how poor sleep impacted these biomarkers. They looked at whether boosting sleep quality may have a beneficial impact for people who are in the preclinical phase of the disease, which show a number of biomarkers but have yet to develop symptoms.

"Previous evidence has shown that sleep may influence the development or progression of Alzheimer's disease in various ways," said study author Barbara Bendlin of the University of Wisconsin-Madison, in a statement.

"For example, disrupted sleep or lack of sleep may lead to amyloid plaque buildup because the brain's clearance system kicks into action during sleep. Our study looked not only for amyloid but for other biological markers in the spinal fluid as well."

Spinal fluid is clear, colourless fluid that is found in the brain and spinal cord and can tell a lot about the state of someone's brain.

Investigating the spinal fluid

In this study, 101 men and women with a mean age of 63 years and with no cognitive problems were recruited. Despite not having any issues with their memory and thinking skills, they were considered at risk of developing Alzheimer's disease, either because one of their parents had had the disease or because they carried a gene that increases the risk of developing it.

They were asked to fill in a survey about the quality of their sleep and samples of their spinal fluid were collected and tested for biological markers of the disease - including signs of the amyloid and tau proteins as well as brain cell damage and inflammation.

The researchers found that people who reported worse sleep quality, more sleep problems and daytime sleepiness also had more biological markers for Alzheimer's disease in their spinal fluid than people who did not trouble sleeping.

These findings indicate that there is an association between poor sleep and preclinical signs of the disease. Looking for people who struggle to sleep could help pinpoint those more at risk of developing Alzheimer's and to design interventions to reduce the risk. The study confirms that improving the quality of their sleep could potentially delay the onset of symptoms, helping people live healthier for longer.

"It's still unclear if sleep may affect the development of the disease or if the disease affects the quality of sleep," Bendlin concluded.

"More research is needed to further define the relationship between sleep and these biomarkers. There are already many effective ways to improve sleep. It may be possible that early intervention for people at risk of Alzheimer's disease may prevent or delay the onset of the disease."