• Researchers estimate that every three seconds, someone in the world develops dementia.
• Inadequate sleep is a modifiable risk factor for dementia.
• A new study says as little as a 1% reduction in deep sleep each year for people over 60 years of age equals a 27% increased risk of developing dementia.

There are currently more than 55 million people around the world living with dementia, and researchers estimate that someone in the world develops dementia every three seconds.

As the number of people with dementia is expected to hit about 153 million by 2050, researchers have been working hard to find more ways to lower a person’s risk of developing this neurological disease.

Many researchers believe inadequate sleep is a modifiable risk factor for dementia.

Now, a new study provides more proof by finding that as little as a 1% reduction in deep sleep — also called slow-wave sleep — each year for people over 60 years of age equals a 27% increased risk of developing dementia.

The findings were recently published in JAMA Neurology.

Clarifying the link between sleep, aging, and dementia risk

For this study, researchers from Monash University in Melbourne, Australia examined data from 346 study participants over the age of 60 enrolled in the Framingham Heart Study. All of the chosen participants had completed two overnight sleep studies, with about five years between each sleep study.

Researchers reported that, on average, the amount of deep sleep each participant had declined between the two studies, indicating slow-wave sleep loss due to aging.

Scientists also followed the study participants from the time of their second sleep study until 2018, looking for dementia diagnoses.

“Responding to the rising prevalence of dementia is one of the most critical challenges of our time,” Dr. Matthew Pase, associate professor at the Monash School of Psychological Sciences and the Turner Institute for Brain and Mental Health in Melbourne, Australia, and senior author of this study told Medical News Today.

“Since we don’t have any readily available curative treatments to halt or reverse dementia permanently, we were interested in understanding ways in which dementia can be prevented in the first instance,” he said.

“For the purpose of informing dementia prevention guidelines, we were interested in clarifying how sleep changed with aging and whether changes in sleep with aging were associated with dementia risk,” he added.

Decreased deep sleep increases dementia risk

Upon analysis, the research team found a total of 52 cases of dementia.

Even after adjusting for a variety of factors, including age, sex, and sleeping medication use, researchers found each percentage decrease in deep sleep each year was associated with a 27% increase in the risk of dementia.

“We know that deep sleep is critical for an aging brain. It helps remove metabolic waste from the brain and also to consolidate memories. It also helps to protect against other dementia risk factors, like high blood pressure. Therefore, we were not surprised to see that greater declines in deep sleep were associated with a higher risk of dementia.”
— Dr. Matthew Pase

The scientists also reported that, on average, the amount of deep sleep each study participant had declined between the two sleep studies, indicating slow-wave sleep loss due to aging.

“Good quality sleep is important for many aspects of health, but poor sleep is not really thought of as a dementia risk factor. These findings further reinforce the need for adults to prioritize good sleep as part of a healthy lifestyle,” Dr. Pase said.

“Much like people make time to fit physical activity into their schedule, people should also make time for sleep of sufficient quality and duration. Doctors can educate adults on strategies to optimize sleep and also help to screen for sleep disorders,” he added.

What is deep sleep? 

Medical experts suggest most adults get between seven to nine hours of sleep each night.

There are four main cycles the body goes through during sleep — three cycles of non-REM (rapid eye movement) sleep and one of REM sleep.

The first two non-REM cycles occur as the body begins to fall asleep.

The third non-REM cycle is known as deep sleep. This is the longest of the three non-REM cycles. At this time, the body’s heart rate and breathing slows, and brain waves become slower and larger.

It is normally very hard to wake up during the deep sleep cycle.

During deep sleep, the body replenishes its energy, regenerates cells, and grows and repairs any tissues and bones.

Past studies also show deep sleep helps strengthen the body’s immune system. It also plays an important role in keeping the brain healthy by helping with developing and storing memories, cognitive function, and efficient learning.

Why does deep sleep affect dementia? 

Because deep sleep plays an important role in keeping the brain healthy, not getting enough sleep can increase a person’s risk of developing brain-related diseases such as dementia, including Alzheimer’s disease.

A study published in April 2021 found people in their 50s and 60s who slept six hours or less each night had a higher risk of developing dementia later in life.

Research published in June 2021 reported that deep sleep may help clear out toxic proteins from the brain related to Alzheimer’s disease.

A study published in May 2023 provided evidence suggesting deep sleep may help protect against memory loss in older people who have a high amount of beta-amyloid in the brain, which is considered to be a main driving factor for developing Alzheimer’s disease.

Tips for better sleep

Medical News Today also spoke with Dr. David Merrill, a geriatric psychiatrist and director of the Pacific Neuroscience Institute’s Pacific Brain Health Center in Santa Monica, CA, about this study.

He said that this study has several implications, including that loss of slow-wave sleep could be a potentially modifiable risk factor for dementia, the most common cause of which is Alzheimer’s disease.

“We know that age and genetics are non-modifiable risks, but the good news is that we are figuring out there are a number of ways to improve the modifiable risks, (of) which sleep quality is definitely one,” Dr. Merrill said.

When asked about how people can get enough sleep to help possibly lower their dementia risk, Dr. Merrill said to focus on habits and behavioral strategies.

“Things like lowering stress levels as we head towards bedtime, taking a warm shower or bath, sleeping in a colder room at a lower temperature — all these have been tied to possibly improving the quality of sleep during the night. We also know about things like avoiding screen time later in the afternoon and into the evening (and) filtering out blue light.”
— Dr. David Merrill

Dr. Merrill also urged caution when considering the use of sleeping pills.

“Unfortunately, there’s no shortcut to getting a good night’s sleep,” he said.

“Traditional sedatives don’t improve the quality or amount of sleep, including they don’t improve amounts of deep sleep. Medications like sleeping pills can (play) a bit of a trick on the brain, thinking that the sedation means that you slept well when, in fact, the data shows that they don’t actually increase the quality or duration of total sleep beyond a few minutes per night,” he explained.

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