After following nearly 8,000 people for 25 years, the study found a higher dementia risk with a “sleep duration of six hours or less at age 50 and 60” as compared to those who slept seven hours a night.
In addition, persistent short sleep duration between the ages of 50, 60 and 70 was also associated with a “30% increased dementia risk,” independent of “sociodemographic, behavioural, cardiometabolic, and mental health factors,” including depression, the study said.
“Sleep is important for normal brain function and is also thought to be important for clearing toxic proteins that build up in dementias from the brain,” said Tara Spires-Jones, who is deputy director of the Centre for Discovery Brain Sciences at The University of Edinburgh in Scotland, in a statement. Spires-Jones was not involved in the study.
“What’s the message for us all? Evidence of sleep disturbance can occur a long time before the onset of other clinical evidence of dementia,” said Tom Dening, who heads the Centre for Dementia at the Institute of Mental Health at the University of Nottingham in the UK, in a statement.
“However, this study cannot establish cause and effect,” said Denning, who was not involved in the study. “Maybe it is simply a very early sign of the dementia that is to come, but it’s also quite likely that poor sleep is not good for the brain and leaves it vulnerable to neurodegenerative conditions like Alzheimer’s disease.”
Chicken or egg?
But does poor sleep lead to dementia — and which comes first? This “chicken and egg” question has been explored in prior studies, with research pointing both ways, according to neuroscientist Jeffrey Iliff, a professor of psychiatry and behavioral sciences at the University of Washington School of Medicine.
Some recent studies, however, have explored the damage sleep deprivation may cause.
A week of disrupted sleep increased the amount of tau, another protein responsible for the tangles associated with Alzheimer’s, frontal lobe dementia and Lewy body disease, the study found.
“The fact that we can find these effects in people who are cognitively healthy and close to middle age suggest that these relationships appear early, perhaps providing a window of opportunity for intervention,” Bendlin said.
‘New information’ on link with sleep deprivation
Because the new study followed a large population over an extended period of time, it adds “new information to the emerging picture” on the link between sleep deprivation and dementia, said Elizabeth Coulthard, an associate professor in dementia neurology at the University of Bristol in the UK, in a statement.
“This means that at least some of the people who went on to develop dementia probably did not already have it at the start of the study when their sleep was first assessed,” said Coulthard, who was not involved in the study.
“It strengthens the evidence that poor sleep in middle age could cause or worsen dementia in later life,” she said.
At this time, science has no “sure-fire way to prevent dementia,” but people can change certain behavior to reduce their risk, said Sara Imarisio, who heads strategic initiatives at Alzheimer’s Research UK, in a statement. Imarisio was not involved in the study.