Skipping this sleep stage could be a problem for your future brain
Key Takeaways
A study published in JAMA Neurology found that a decrease in slow-wave sleep is associated with Alzheimer's disease (AD) and dementia.
Slow-wave sleep is the deepest stage of sleep. Experts say that it “washes” the brain of impurities associated with AD and dementia.
Good sleep hygiene is key, especially in older patients, as slow-wave sleep decreases with age.
A recent study published in JAMA Neurology found that getting deep sleep (also known as slow-wave sleep) may reduce Alzheimer's disease (AD) and dementia risk.
“Slow-wave is considered the stage where sleep is the deepest, and it’s the hardest to wake up out of,” William Lu, MD, a sleep medicine physician and Medical Director of Dreem Health, tells MDLinx. “It takes up a portion of the night’s sleep, [so] if you sleep 7 to 8 hours, you’re gonna have some parts of deep sleep—unless you have sleep apnea or interruptions.” How much slow-wave sleep each person gets varies.
What is slow-wave sleep?
Lauri Leadley, a clinical sleep educator at Valley Sleep Center, explains the sleep cycle in more detail: “A normal sleep cycle takes no less than 90–110 minutes per cycle, and if the body isn’t cycling through from start to finish—wake, light sleep, deep sleep, REM (vivid dreaming)—at least four to six cycles per night, you’re not getting good sleep,” she says.
Slow-wave sleep plays an incredibly important role: It ‘bathes’ the brain, Dr. Lu says. “There’s a potential process happening [during SWS] that cleanses the brain from what we’ll call ‘impurities,’” he explains. During SWS, the waves “actually move cerebrospinal fluid through the brain, [so it’s] hypothesized to be ‘bathing’ the brain.”
This cleansing process is associated with a lower risk of Alzheimer's disease and dementia, so with limited SWS, there’s less opportunity for the cleansing process.[]
A closer look at the study
To understand the connection between SWS and AD and dementia risk, the researchers analyzed data from the Framingham Heart Study.[] The study included 346 patients (52% female, 84% White) who were 60 years and older (mean age of 69) who completed two overnight polysomnography (PSG) studies between 1995 and 1998 and 2001 and 2003 and did not have dementia at the time of the second study.
The researchers found that “after further adjustments for positivity for at least 1 APOE ε4 allele, smoking status, sleeping medication use, antidepressant use, and anxiolytic use, each percentage decrease in SWS per year was associated with a 27% increase in the risk of all-cause dementia and a 32% increase in the risk of AD dementia.” It’s notable that SWS loss due to aging was exacerbated among those with the APOE ε4 allele, which is associated with AD genetic risk.
Sleep hygiene for both older and younger patients
“If [a patient] is napping frequently throughout the day or feel[s] chronically fatigued and tired, it’s time for a sleep study to get to the root cause of the issue,” Leadley says. This is especially true for aging patients: “We know [that] as you age, or if you have insomnia, you naturally have less SWS,” Dr. Lu says. As we get older, hormonal fluctuations are responsible for the reduction in SWS.
For younger patients, however, lifestyle also plays into SWS.
Dr. Lu says that the basics of sleep hygiene are everything: “Get enough sleep: Go to bed at a regular time and wake at regular time. And have a sleep ritual. These things can help to promote more sleep, he says. “This is the base of the cake.”
More so, patients should be encouraged to think of their waking behaviors as helpful for sleep later on that day. “Make sure you’re living a healthy lifestyle. Exercise in the early afternoon can help increase the deepest sleep,” Dr. Lu adds.
Leadley also notes that patients should make sure to soak up some sun every day; stop the use of substances like caffeine, nicotine, or alcohol, especially later in the day; get proper treatment for chronic pain; adjust time frames for taking medications; and challenge their cognitive skills with brain games and activities.
Dr. Lu also says that there are well-researched drugs that can be given for sleep disorders; however, each drug has a very different effect. “Some can increase SWS,” he says. It’s good to check available resources on a drug’s side effects before prescribing.
Dr. Lu was a primary care doctor before specializing in sleep medicine, so he knows that clinicians generally don’t get enough— if any—sleep training. So, it’s important to refer patients to a sleep specialist if their symptoms are beyond your scope. Another issue you may notice is that sleep clinics are often full, meaning it takes a while for patients to find care. In this case, Dr. Lu says, telehealth is also a good option.