Loss of slow-wave sleep as you age may increase your risk of developing dementia, according to a new study.
"We found that aging was associated with a decline in the amount of the deepest stages of sleep, known as slow wave sleep,” said Matthew P. Pase, senior author of the study published Monday in the journal JAMA Neurology, via email. Pase is an associate professor of psychology and neurology at Monash University in Australia.
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, said Dr. Richard Isaacson, director of research at the Institute for Neurodegenerative Diseases in Florida, via email. Isaacson wasn’t involved in the study.
The authors wanted to know whether chronic reductions in slow-wave sleep over time are linked with dementia risk in humans and vice versa — whether dementia-related processes in the brain may contribute 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 age 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% increased risk of developing dementia and a 32% 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 afterward.
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 APOE ε4 allele).
"This is an important study yet again showing the impact of quality of sleep on a person’s risk of cognitive decline and dementia,” Isaacson said. “It’s important to not only pay attention to the total amount a person is sleeping each night, but also monitor sleep quality as best as possible.”