A correlation has been found between dementia and a decrease in the deep stage of sleep

Losing slow-wave sleep as you age may increase your risk of developing dementia, according to a new study, CNN reports.

“We found that aging was associated with a decline in the deepest stages of sleep, known as slow-wave sleep,” Matthew P. Pace, senior author of the study published Monday in JAMA Neurology, said in an email. Pace is an associate professor of psychology and neuroscience at Monash University in Australia.

“We then found that people with greater declines in slow-wave sleep over time had a higher risk of developing dementia over the next 17 years of follow-up,” says Pace.

Slow wave sleep is the third stage of sleep and is important for brain health, CNN explains. During this stage, the body removes unwanted or potentially harmful substances from the brain, including beta-amyloid protein, a hallmark of Alzheimer’s disease.

This deep sleep is thought to be the most restorative for the brain, says Dr. Richard Isaacson, director of research at the Florida Institute for Neurodegenerative Diseases.

The study authors wanted to know whether a chronic decline in slow-wave sleep over time is associated with people’s risk of developing dementia, and vice versa – whether processes associated with dementia in the brain might contribute to a decrease in the duration of this type of sleep.

“The results suggest that chronic decline in slow-wave sleep, rather than individual differences at any one time point, is important for predicting the risk of developing dementia,” says Matthew Pace.

The researchers studied 346 people with an average age of 69 who participated in the Framingham Heart Study and completed two overnight sleep studies—one between 1995 and 1998 and one between 1998 and 2001—that monitored their sleep. The Framingham Heart Study, conducted by the National Heart, Lung, and Blood Institute, identifies common factors that contribute to the development of cardiovascular disease.

The authors also examined whether any changes in the amount of slow-wave sleep participants received were associated with the development of dementia up to 17 years after completing the sleep studies.

By that time, 52 participants had been diagnosed with dementia. Each percentage reduction in slow-wave sleep duration per year was associated with a 27% increased risk of dementia and a 32% increased risk of Alzheimer’s dementia. The rate of slow-wave sleep loss accelerated from age 60, peaked between ages 75 and 80, and then slowed down.

Those who experienced worsening of this deep sleep were more likely to have cardiovascular disease, take medications that affect sleep, and carry a gene that increases the risk of developing Alzheimer’s disease (the APOE ε4 allele).

“This is an important study that further demonstrates the impact of sleep quality on a person’s risk of cognitive decline and dementia,” said Dr. Isaacson. “It is important not only to pay attention to the total amount of sleep a person gets each night, but also to monitor the quality of sleep as much as possible.”

This study is not the first to find such connections—in the May study, each 10% decrease in deep sleep duration was associated with an increase in damage to the tissues that form connections between brain cells.

But the latest research still doesn’t prove that loss of slow-wave sleep causes dementia, the study authors say, and it’s also possible that dementia-related processes in the brain may lead to sleep loss – a process one expert called a “vicious cycle.”

“The accumulation of beta-amyloid in the brain may influence how much sleep we get, especially as we age,” says Dr. Rudolf Tanzi, director of genetics and aging research at Massachusetts General Hospital.

“As a result, due to insufficient slow-wave sleep, less amyloid is eliminated, leading to a vicious cycle of Alzheimer’s pathology,” he added. “So safe drugs aimed at reducing amyloid production will be important.”

Pace advised people to prioritize getting good sleep. “Good quality sleep is important for many aspects of health and can also help protect the brain as we age,” he said. “People experiencing sleep problems can consult with their doctor to discuss individual solutions.”

If deep sleep “does turn out to be a proven modifiable risk factor for Alzheimer’s disease and dementia, then we need to give people the ability to track their sleep more closely,” Isaacson said.

For this purpose, he recommended wearing tracking devices that can track your stay in bed, sleep time, and time spent in each sleep stage. These devices are not perfect, the expert cautioned, but “they can at least provide people at risk and their doctors with real-time information on which to act.”

Adopting a few good habits—another thing that tracking devices could measure their effectiveness—can also help protect your sleep and brain health.

“Regular exercise helps ‘release’ harmful disease-causing proteins called amyloid from brain cells, and getting enough deep sleep at night to ‘clear out’ amyloid debris,” advises Dr. Isaacson.

Limiting alcohol and caffeine consumption before bed and ensuring you get seven to nine hours of sleep at the same time each night can help improve sleep quality.