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A lack of sleep accelerates the spread of toxic lumps that cause dementia throughout the brain, warns new research.
Alzheimer's disease, which affects more than 500,000 people in Britain and 5.7 million Americans, has long been linked to a bad night's sleep.
But until now, little was known about how sleep disorders led to illness.
The new study in humans and mice revealed that sleep deprivation increased Alzheimer's key tau protein levels.
And, in follow-up studies in mice, researchers at Washington University's School of Medicine in St. Louis showed that insomnia accelerated the spread of toxic tau bunches into the brain.
It is not clear if lack of sleep causes acceleration or if acceleration causes lack of sleep but there seems to be a clear badociation (file image)
The Tau are a harbinger of brain damage and a decisive step on the road to dementia.
The study, published in the journal Science, indicates that the only lack of sleep contributes to the prophylaxis of the disease and suggests that a good night's sleep could help preserve brain health.
Dr. David Holtzman, senior author and director of the Department of Neurology, said, "What's interesting in this study is that it suggests that real factors, such as sleep, could affect the rate at which the disease spreads in the brain.
"We know that sleep problems and Alzheimer's disease are badociated in part with a different protein from Alzheimer's – the beta-amyloid – but this study shows that sleep disturbances cause a rapid increase in tau protein, a harmful protein, and its spread over time.
"We should all try to have a good night's sleep.
"Our brains need time to recover from the stress of the day.
"We do not know yet whether sleeping well as we get older will protect against Alzheimer's disease.
"But that can not hurt, and this and other data suggest that it might even help to delay and slow down the disease process if it started."
Tau is normally found in the brain – even in healthy people – but under certain conditions it can clump into an entanglement that damages nearby tissues and predicts cognitive decline.
Recent research at the Faculty of Medicine has shown that tau is high in older people who sleep poorly.
But it was not clear whether lack of sleep directly forced tau levels to increase, or whether the two were badociated in some other way.
The researchers measured tau levels in mice and people with normal and disturbed sleep.
Mice are nocturnal creatures and researchers found that tau levels in the fluid surrounding brain cells were about twice as high at night, when animals were awake and more active, than during the day when mice slumber more frequently.
The disruption of mice rest during the day doubled tau levels during the day.
The same effect has been observed in people.
Dr. Brendan Lucey, an badistant professor of neurology, got the cerebrospinal fluid – which bathes the brain and spinal cord – after a normal night's sleep and after keeping it awake all night long.
A sleepless night resulted in an increase in tau levels of about 50%.
Staying awake makes people stressed, cranky and likely to sleep at the next opportunity.
But scientists have ruled out stress or behavioral changes for changes in tau levels in experiments on mice.
And the mice that have been awake for long periods have caused an increase in tau levels.
Overall, the results suggest that the normal task of thinking and doing releasing tau regularly during waking hours, and that this release is reduced during sleep, which helps to rid it of tau.
Sleep deprivation interrupts this cycle, allowing the tau protein to accumulate and increasing the risk of protein accumulation in harmful entanglements.
In people with Alzheimer's disease, tau tangles tend to appear in parts of the brain important for memory – the hippocampus and the entorhinal cortex – and then spread to other people. other areas of the brain.
As tau mires mushrooms and more and more areas are affected, people are finding it increasingly difficult to think clearly.
To investigate whether the spread of tau tangles is affected by sleep, researchers seeded the mouse hippocampus with tiny tufts of tau and then kept the animals awake for long periods each day.
A separate group of mice were also injected with tau entanglements, but were allowed to sleep when they wished.
After four weeks, tau tangles had spread more in sleep-deprived mice than in their resting counterparts.
Notably, new entanglements have appeared in the same areas of the brain affected by people with Alzheimer's disease.
The researchers also found that sleep disturbance increased the release of the synuclein protein characteristic of Parkinson's disease.
People with Parkinson's – like those with Alzheimer's – often have problems sleeping.
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