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.
"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," said Pase via email.
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 percent increased risk of developing dementia and a 32 percent 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."
Deep sleep and dementia
The study isn't the first to find such connections - in a May study, every 10 percent 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."
"The accumulation of amyloid beta in the brain can interfere with how much we sleep, especially as we age," said Dr Rudolph Tanzi, director of the Genetics and Aging Research Unit at Massachusetts General Hospital, via email. Tanzi wasn't involved in the study.
"As a result, by not getting enough slow wave sleep, less amyloid is cleared, then leading to a vicious cycle of Alzheimer's pathology," he added via email. "Thus, safe drugs aimed at lowering production of amyloid will be important."
Getting more deep sleep
Pase advised people to prioritise getting good sleep. "Good quality sleep is important for many aspects of health and may also help to protect the brain as we age," he said. "Persons experiencing sleep problems can consult with their doctor to discuss tailored solutions."
If deep sleep "does turn out to be a proven modifiable risk factor for Alzheimer's and dementia, then we need to empower people to be able to track and monitor (their sleep) more closely," Isaacson said.
For this purpose, he recommended wearing tracking devices that can monitor your time in bed, time asleep and time spent in each sleep stage.
These devices aren't perfect, he cautioned, but "they can at least give people at risk, and their physicians, real-time information that can be acted upon."
Adopting a few healthy habits - another thing tracking devices would be able to indicate the effectiveness of - may also help protect your sleep and brain health.
"Exercise on a regular basis helps 'loosen up' the bad (disease-causing) proteins - called amyloid - from brain cells, and adequate deep sleep is necessary at night to 'take out' the amyloid trash," Isaacson said.
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.
CNN
