New research finds link between sleep and dementia

A new study has found enhancing or maintaining deep sleep in older years could prevent dementia.

Led by Associate Professor Matthew Pase from Monash University, the study discovered that a yearly reduction of as little as one per cent in deep sleep (or slow-wave sleep) for individuals over the age of 60 correlated with a 27 per cent increase in the risk of dementia.

The study looked at 346 participants over the age of 60, who completed two overnight sleep studies one between 1995 and 1998, and another from 2001 to 2003.

The researchers found, on average, that the amount of deep sleep declined between the two studies – indicating slow-wave sleep was lost with aging.

From 2003 to 2018, the participants were followed to see if they had any dementia symptoms, with 52 participants developing dementia in that time.

Professor Pase said the slow-wave sleep and dementia were linked, and with this research, it was evident how interlocked these factors were.

"Slow-wave sleep supports the aging brain in many ways," he said.

"We know that sleep augments the clearance of metabolic waste from the brain, including facilitating the clearance of protein that aggregates in Alzheimer's disease."

"However, to date, we have been unsure of the role of slow-wave sleep in the development of dementia ... our findings suggest that slow-wave sleep loss may be a modifiable dementia risk factor."

More than 400,000 Australians live with dementia, with 70 per cent of aged-care residents living with moderate to severe cognitive impairments, including dementia.

That number is estimated to jump to 900,000 in the next 25 years, with the recent Intergenerational Report estimating Australia's older population to triple.

Professor Pase said repeated overnight polysomnographic (PSG) sleep studies and uninterrupted surveillance for incident dementia helped to find the link between the two.

"We used [these] to examine how slow-wave sleep changed with ageing and whether changes in slow-wave sleep percentage were associated with the risk of later-life dementia up to 17 years later,” he said.

“We also examined whether genetic risk for Alzheimer’s Disease or brain volumes suggestive of early neurodegeneration was associated with a reduction in slow-wave sleep."

"We found that a genetic risk factor for Alzheimer’s disease, but not brain volume, was associated with accelerated declines in slow-wave sleep.”

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