Sleep deprivation speeds up Alzheimer’s brain damage, study says

Disrupted sleep appears to speed-up the formation of the toxic substances in the brain which lead to memory loss and a cognitive decline in Alzheimer’s disease, scientists have found.

Abnormal protein molecules, known as tau, which can form sticky clumps and tangles capable of damaging neurons, were found to buildup at an accelerated pace when test subjects were kept awake.

The findings suggests that techniques to improve sleep could help “slow down the disease” once it’s begun, according to the team from the University of Washington who published their findings in the journal Science.

Tau protein is present in the brains of healthy people and is released as neurons send signals to one another, but in Alzheimer’s disease it builds up to damaging levels, starting in the regions linked to memory and spreading through the brain.

The study found that tau appears to be produced when the brain is engaged in thinking and daily tasks, but then dissipates overnight in periods of deep sleep.

Interfering with this process for a prolonged period caused it to buildup at an accelerating rate and increases the chances of damaging clumps beginning to form.

“The interesting thing about this study is that it suggests that real-life factors such as sleep might affect how fast the disease spreads through the brain,” said Professor David Holtzman, the study's senior author.

While it was known that dementia patients get less sleep, the physical link had previously been seen with a different protein – known as beta amyloid – which isn’t as damaging as tau.

Damaging tangles of tau tend to emerge first in the brain’s memory centres – the hippocampus and entorhinal cortex – but as they spread to other areas of the brain it causes the disease’s gradually progressing effects.

To test these effects Professor Holtzman and colleagues first used mice, which are nocturnal, and found their tau levels doubled while they were active at night.

When they disrupted their sleep to keep them active in the day they found tau in the brain doubled as well.

Tests on cerebrospinal fluid – which bathes the brain and spinal cord – from eight human patients after they’d had a good night’s sleep and one where they had been kept awake found that a sleepless night led to tau levels rising 50 per cent.

To ensure this wasn’t just caused by the stress of being kept awake, they also ran tests in mice genetically modified to be able to stay awake for prolonged periods without increases in stress hormones.

“Getting a good night’s sleep is something we should all try to do,” Professor Holtzman added. “Our brains need time to recover from the stresses of the day. We don’t know yet whether getting adequate sleep as people age will protect against Alzheimer’s disease.

“But it can’t hurt, and this and other data suggest that it may even help delay and slow down the disease process if it has begun.”