Loss of slow-wave sleep as you age may increase your risk of developing dementia, according to a new Australian study.
"We found that aging was associated with a decline in the amount of the deepest stages of sleep, known as slow wave sleep," Matthew P. Pase, an associate professor of psychology and neurology at Monash University in Melbourne, said.
"We then found that persons with greater declines in slow wave sleep over time had a higher risk of getting dementia over the next 17 years of follow-up."
Slow-wave sleep is the third stage of sleep, which is important for brain health.
During this stage, the body removes unwanted, or potentially harmful, materials from the brain — including beta-amyloid protein, a hallmark sign of Alzheimer's disease.
For the brain, this deep sleep is thought to be the most restorative.
The study, which was published in journal JAMA Neurology, sought to find out if chronic reductions in slow-wave sleep over time are linked with dementia risk.
Pase also wanted to determine if dementia-related processes in the brain contributed to getting less of this type of sleep.
"Results suggest that chronic declines in slow wave sleep, rather than individual differences at any given time, are important for predicting dementia risk," Pase said.
The researchers studied 346 people who were aged 69 on average and had participated in the Framingham Heart Study and completed two overnight sleep studies — one between 1995 to 1998 and the second between 1998 to 2001 — during which their sleep was monitored.
Launched by the US National Heart, Lung and Blood Institute in 1948, the Framingham Heart Study identifies common factors contributing to cardiovascular disease.
The authors also investigated whether any changes in the amount of slow-wave sleep that participants got was associated with developing dementia up to 17 years after they completed the sleep studies.
By that time, 52 participants had been diagnosed with dementia.
Each percentage decrease in slow-wave sleep per year was linked with a 27 per cent increased risk of developing dementia and a 32 per cent higher risk of Alzheimer's disease dementia.
The rate of slow-wave sleep loss accelerated from age 60, peaked from ages 75 to 80 and slowed afterwards.
Those who experienced declines in this deep sleep were more likely to have cardiovascular disease, take medications that affect sleep and carry a gene that makes people more at risk for Alzheimer's.
The study isn't the first to find such connections.
In a May study, every 10 per cent decrease in deep sleep meant an increase in damage to tissues that form connections between brain cells.
But the latest research still doesn't prove that loss of slow-wave sleep causes dementia, the authors said, and it's also possible that dementia-related processes occurring in the brain could lead to the sleep loss — a process one expert called a "vicious cycle".
Pase advised people to prioritise getting good sleep.
Limiting alcohol and caffeine before bed, and ensuring you get seven to nine hours of sleep at the same time each night, can help improve sleep quality.
