People in their 30s and 40s who are not getting enough sleep could find themselves with dementia by their 60s, sleep expert Michael Chee has warned.
He issued the warning, as growing evidence has shown that adequate sleep is necessary to clear the accumulation of "junk" in the brain, which is linked to Alzheimer's Disease, the most common form of dementia that can result in extreme forgetfulness.
Professor Chee, director of the Centre for Cognitive Neuroscience at Duke-NUS, told The Straits Times that a paper published in 2013 showed that sleep helps clear metabolites - the junk that develops when the brain processes the energy it needs - in adult brains.
While doctors are not sure if it is the protein beta amyloid - the junk that Prof Chee spoke of - that causes Alzheimer's, they do know that there is a huge amount of these proteins in the brains of people with Alzheimer's.
Prof Chee said that as people get older, their ability to clear this junk from their brain is diminished.
Sleep is important in helping to clear away these proteins, he noted, adding that the rate of clearance is about six times during sleep, compared with when people are awake.
"If you are sleep deprived, the rate of clearance of this beta amyloid is reduced, so you have more junk floating around in the brain," he said.
It is like having a blocked sewerage system in the brain, he said. As the sewage piles up, there comes a time when there is so much that this does damage to the brain.
Pharmaceutical companies have invested billions of dollars trying to produce medicine that can clear the beta amyloid from the brain, but have yet to succeed, he said.
It takes years of accumulation for damage to be done, typically 10 to 20 years, said Prof Chee.
That is why people in their middle years, who do not get enough sleep, could find themselves suffering from Alzheimer's, becoming forgetful by the time they are in their late 50s or 60s.
In general, he said, people need at least 61/2 to seven hours of sleep a night, with peak performance generally associated with seven hours of sleep.
Busy people often think they can get by with four to five hours of sleep a night, he said, adding that they think it is all right as they can still manage their daily activities.
He said people who use their brains a lot "are able to compensate better and they hide it to a point where they cannot hide it any more, then they go 'bang' and get it very bad".
"By the time you're diagnosed with Alzheimer's, it's too late. The house has... burned down," he added.
However, he admitted that more studies are needed, as it is still not known if sleeping longer over weekends, for example, can help clear the backlog of beta amyloids and, if so, to what extent.
Similarly, is just having seven hours of sleep a night enough, or must it be deep sleep?
Nevertheless, he said, it is irrefutable that having enough sleep is critical for good health.
Aside from getting dementia, insufficient sleep is known to raise the risk of diabetes, some cancers, heart attacks and stroke.
"If you take care of your sleep, you can improve many aspects of your health," he said.
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