Chronic Poor Sleep Linked to Increased Risk of Alzheimer’s Disease

Regular disruption of a good night’s sleep, especially slow wave sleep in otherwise healthy middle aged adults might put them at an increased risk of Alzheimer’s disease (AD) later in life, according to a recent study conducted by Washington University School of Medicine in St. Louis, Radboud University Medical Centre in the Netherlands, and Stanford University. The findings of the study appeared in the journal Brain.

Poor Sleep And Cognitive Impairment – Possible Link To Alzheimer’s Disease?

Previous research by Holtzman, co-first author Yo-El Ju, MD, an assistant professor of neurology, and others have shown that persons with chronic sleep problems, like sleep apnea develop cognitive impairment significantly earlier compared to good sleepers.

Also, one of the earliest signs of Alzheimer’s disease, a neurodegenerative condition is impaired cognition.

Based on the association between poor sleep and cognitive impairment, the study team wanted to carry the research forward and determine the reason for cognitive impairment in persons with chronic poor sleep and whether this could be a possible piece in the puzzle of Alzheimer’s disease.

"We think that perhaps chronic poor sleep during middle age may increase the risk of Alzheimer's later in life", says Holtzman.

Finding the Reason for Brain Damage in Sleep Deprived Persons

In order to get to the bottom of the matter, the team comprising of Holtzman; Ju; co-first author and graduate student Sharon Ooms of Radboud; Jurgen Claassen, MD, PhD, of Radboud; Emmanuel Mignot, MD, PhD, of Stanford; and colleagues studied 17 healthy adults aged between 35 to 65 with no sleep problems or cognitive issues.

• Initially, each participant was given an activity monitor to wear that tracked how much they slept at night for a period of five days
• Following this, each volunteer came to the School of Medicine to a specially designed Sleep Room, the perfect place for a night’s rest – dark, soundproofed and climate controlled and just large enough for one person.
• Here, they were fitted with headphones and electrodes on the scalp to monitor brain activity and wave pattern.
• Half the participants were randomly chosen to have their sleep disturbed during the night they spent in the Sleep Room. Whenever the participants drifted into slow wave pattern deep sleep, they were disturbed by a series of beeps via their headphones, getting louder until their deep sleep was disturbed and they entered shallower sleep
• The next morning, the persons whose slow wave sleep had been disturbed reported feeling tired and lethargic although they had slept the entire time and could not recollect being woken up.
• All the participants underwent a spinal tap to measure levels of amyloid-beta and tau proteins (known to be elevated in AD) in their cerebrospinal fluid (CSF).
• The same process was repeated a month letter. Only, this time the roles were reversed and the persons who were disturbed during their sleep earlier were now allowed to sleep uninterrupted and vice versa. Again, a spinal tap was performed to measure the levels of the beta-amyloid and tau proteins.
• The study team compared the levels of amyloid-beta and tau proteins in the participants on the night the sleep was interrupted and the night they slept without any disturbances in the Sleep room.
• Following a single night interrupted sleep there was a ten percent increase in beta-amyloid levels but tau protein remained unchanged.
• However, the individuals who had slept poorly at home during monitoring of sleep through activity monitor showed a rise in tau protein levels.

"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," Ju said. "But we could see, when the participants had several bad nights in a row at home, that their tau levels had risen."

How Disrupted Slow Wave Sleep can Cause Brain Damage

It is during the deep sleep (slow wave sleep) that the nerve cells rest and the accumulated toxic metabolites and products during the day when the brain is constantly thinking and functioning are cleared by the cell scavenging mechanisms.

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Therefore, disturbed slow wave sleep interferes with cell scavenging and clearing and allows accumulation of harmful proteins such as tau and beta-amyloid that can cause nerve cell damage and death.

This may not be of consequence if sleep is occasionally disturbed; in this case the elevated proteins will return to baseline levels when proper sleep is restored. The danger is in those with chronic sleep deprivation.

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"The main concern is people who have chronic sleep problems," Ju said. "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."

Alzheimer’s Disease in Brief

Alzheimer’s disease is a neurodegenerative brain disease that often is seen in the elderly, characterized by loss of memory and impaired cognition that worsens over time and leaves the person totally dependent on a carer for all activities of daily living.

Currently there are over 5 million Americans living with Alzheimer’s disease and until now there is no treatment to slow or prevent progression of the disease.

The brains of persons with Alzheimer’s disease have been shown to contain amyloid plaques (amyloid-beta protein) and tangles of tau protein.

Conclusion

In conclusion this study does not aim to establish a causal relationship between poor sleep and Alzheimer’s disease. It suggests that poor sleep is associated with accumulation of certain toxic proteins occurring in AD, that can be prevented by a refreshing and fitful night’s rest.

In the words of Ju, co-first author, "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."

Reference:

1. David M. Holtzman et al. Slow wave sleep disruption increases cerebrospinal fluid amyloid-β levels. Brain, July 2017 DOI: 10.1093/brain/awx148

Source-Medindia