Karen Jaffe used to love sleeping, both in bed at night and napping during the day. But since her diagnosis of Parkinson's disease in 2007, the 60-year-old retired physician from Cleveland has come to dread it. For one thing, certain symptoms make it tough for her to get comfortable. "Once I'm lying down, trying to roll over is ridiculous—it's as if I'm frozen there, stiff and rigid, trapped in one position," she says. Jaffe also has rapid eye movement (REM) sleep behavior disorder, a common symptom of Parkinson's disease in which people experience night terrors or try to physically act out their dreams. "My problem is nightmares," she says. "I often wake myself up with my own yelling. I'm lucky if I get four hours of sleep a night."

Like many patients with neurologic conditions, Jaffe takes medication that can interfere with sleep. One such drug, ropinirole (Requip)—which is prescribed for restless legs syndrome and causes impulsive behavior in some people—leaves Jaffe feeling revved up and unwilling to put away a project, no matter how late it gets. "I can't stop whatever I'm doing," she says. The next day she pays the price. "Besides being tired, my tremors are definitely worse."

LISTEN NOW: The neurologist hosts of the Brain & Life podcast discuss the importance of sleep for brain health.

How well we sleep impacts how we think and feel, as well as our alertness, memory, and concentration. "Sleep quality and quantity are directly related to the health of the brain," says Beth A. Malow, MD, MS, FAAN, professor of neurology and director of the sleep disorders division at Vanderbilt University Medical Center in Nashville. Several studies have demonstrated an association between sleep disturbances such as insomnia, fragmented sleep, sleep apnea, and even excessive napping and an increased risk of cognitive decline over time, says Brendan P. Lucey, MD, assistant professor of neurology and director of the sleep medicine section at Washington University School of Medicine in St. Louis.

In 2009, a series of studies on mice conducted at Washington University were among the first to suggest that chronically sleep-deprived subjects develop higher levels of harmful amyloid beta and tau proteins—considered, along with neurofibrillary tangles, to be hallmarks of Alzheimer's disease. "Think of tau and amyloid as the waste produced by typical nerve function," says Charlene Gamaldo, MD, FAAN, associate professor of neurology and medical director of the Johns Hopkins Sleep Disorders Center. "Normally, the brain clears these metabolic waste products away."

And it may clear away these proteins during sleep, according to a landmark 2013 rodent study in Science by researchers at the University of Rochester Medical Center, who showed that during deep sleep, when neural activity quiets down, cerebrospinal fluid (CSF) bathes the brain, washing away excess amyloid beta and tau proteins. A more recent study, published in the November 2019 issue of iScience, provided further insight into CSF's function. MRI scans taken while subjects were sleeping showed that during deep sleep, blood flow in the brain diminished as pulsing waves of CSF flushed out excess amyloid beta and tau, presumably girding the brain against cognitive decline. So while it has been known that sleep has some value for survival, these reports seem to put sleep front and center in terms of protecting us from cognitive decline.

It also may be that less amyloid beta and tau are produced when we sleep than while we're awake, says Dr. Lucey. In a 2018 study in Annals of Neurology, he and his co-authors measured the levels of amyloid beta in sleep-deprived subjects versus those who were allowed to sleep normally; amyloid beta production was 25 to 30 percent higher in the sleep-deprived group.

In other research, scientists are learning the effects that certain sleep problems may have on the brain. A 2018 meta-analysis in Sleep Medicine Reviews of multiple studies involving a quarter of a million people over 10 years showed that people with insomnia had an increased risk of developing Alzheimer's. Those with sleep-disordered breathing, like sleep apnea, had an increased risk of dementia, and those with fragmented, nonrestorative sleep were also more likely to develop Alzheimer's and dementia.

These findings suggest that quality and type of sleep are also important. You should be able to cycle through the two primary stages of sleep—non-REM and REM (when most dreaming occurs)—with minimal interruptions. Non-REM sleep has three subphases: drowsiness, when breathing and heart rate begin to slow; a deeper-sleep phase characterized by brain waves known as sleep spindles; and slow-wave sleep, the most restorative kind, when neural activity and blood flow are at their lowest points and CSF's clearance action kicks in.

All phases of sleep play critical and specific roles in cognitive function and memory consolidation, according to studies. "The spindle activity of stage 2 appears to increase in response to exposure to new information—it's possible that it is a biophysiological marker of learning," says Dr. Gamaldo. A 2018 study in the journal Neuron reported, among other things, that when sleeping subjects had their slow-wave and spindle sleep enhanced in the laboratory, they did better on memory tests the next day.

Slow-wave and REM sleep seem to be linked to both procedural memory (the ability to automatically perform a task, like riding a bicycle) and semantic memory (recall of words, concepts, and numbers). Slow-wave sleep is associated with consolidating memory, whereby things learned in the short term and processed in the hippocampus are stored in the cortex for the long term. "But then again, so is REM sleep," says Dr. Gamaldo, who cites a 2017 study in Neurology that showed that people who get less REM sleep may have a greater risk of developing dementia.

Other Alzheimer's-related research is examining sleep for early markers of the condition. "With Alzheimer's, we know that amyloid deposition can begin more than a decade before a person shows signs of cognitive impairment," says Dr. Lucey. "This means there is the potential to screen a person for changes in sleep to assess their risk for Alzheimer's in a noninvasive way." It also presents the possibility of treating sleep disturbances at an earlier stage—and possibly preserving cognitive function. A 2015 New York University study published in Neurology found that seniors with sleep apnea who used a CPAP (continuous positive airway pressure) machine to help them breathe more easily during sleep experienced signs of mild cognitive decline a full decade later than those with sleep apnea who didn't use a CPAP machine.

These results indicate that cognitive decline does not have to be an inevitable result of aging if people can regularly get a good night's sleep. They should tell their doctor if sleep patterns change, and doctors need to ask about sleep. "The hopeful thing is that most sleep disorders are treatable," says Dr. Lucey. "If you're concerned about your sleep, or you're too tired to do the things you need to do, you really should get medical attention."

Karen Jaffe has worked with her physician to adjust the timing of her medication so it doesn't leave her feeling revved up before bedtime. "People shouldn't feel shy about asking for help managing sleep disturbances," she advises. "Meds can be added or doses and timing can be changed to help you sleep better."

Jaffe, who's a member of the Michael J. Fox Foundation's Patient Council, has adopted other sleep-promoting habits as well. "I try to put my electronics away before bed—that's the main thing," she says, adding, "I feel better when I do yoga, tai chi, or other kinds of exercise during the day. It makes me tired, so I can finally sleep for six or eight hours at a stretch."

Troubleshoot a Sleep Disorder

Do sleep problems affect your life? The answer to that question may reveal whether you have a sleep disorder, says Brendan P. Lucey, MD, director of the sleep medicine section at Washington University in St. Louis. "It's okay if someone needs a short nap," Dr. Lucey says, "but if patients are struggling to function, I'll order a sleep workup."

If you can't sleep at night or stay awake during the day, or you have breathing or other problems while you sleep, see your internist or neurologist for a referral. "Ideally, you'll want them to refer you to a sleep lab or center certified by the American Academy of Sleep Medicine," says Dr. Lucey. "At the minimum, you want to be sure the director is board-certified in sleep medicine." (To find a sleep center near you, go to sleepeducation.org.)

A sleep specialist will ask about your personal habits and sleeping patterns and may recommend a full sleep study, which would take place overnight in a lab or at home. "We don't do a sleep study on everyone who has sleep problems—often, by focusing on sleep hygiene, we can help them get a better night's sleep," says Beth A. Malow, MD, MS, FAAN, director of the sleep disorders division at Vanderbilt University Medical Center in Nashville.

Some sleep disorders are related to neurologic conditions: REM sleep behavior disorder may occur in patients with Parkinson's disease, for example, and circadian rhythm disorder often develops in people with Alzheimer's, says Dr. Malow. Sleep problems among the general population include insomnia, sleep apnea, and restless legs syndrome.

6 Ways to Sleep Better

Despite all the evidence supporting sleep's positive effect on brain health, one in three adults don't get enough sleep, according to statistics from the US Centers for Disease Control and Prevention. Researchers at the University of Pennsylvania Perelman School of Medicine found that 25 percent of Americans experience acute insomnia every year. Furthermore, only 10 percent of adults make sleep a priority over other activities, according to a 2018 poll of more than 1,000 people by the National Sleep Foundation.

A first step in getting more rest is to practice good sleep hygiene, says Beth A. Malow, MS, MD, FAAN, chief of the sleep disorders division at Vanderbilt University Medical Center in Nashville. That means going to bed and waking up at the same time every day; keeping the bedroom cool, dark, and quiet; avoiding caffeine, large meals, and alcohol; and shutting down electronics a few hours before bedtime. She also recommends these additional steps.

1. Sit by a window. We all have an internal body clock: "It regulates our day-to-day alignment with the environment, and our daily exposure to light is what signals it most strongly," says Sabra M. Abbott, MD, PhD, assistant professor of neurology at Northwestern University Feinberg School of Medicine in Chicago. A 2017 study in Current Biology found that people who went camping for a week in winter slept longer and were more energetic during the day than when they were in their offices in artificial light. You don't have to camp, but do what you can to maximize your exposure to natural light-like sitting near a window during the day.
2. Avoid blue light. "All your screen time and exposure to abnormal light can suppress the production of melatonin, which not only makes it difficult to sleep but increases the risk for other health problems," says Dr. Abbott. A 2015 study in the Proceedings of the National Academy of Sciences found that students who used e-readers at maximum brightness showed disruptions in their circadian rhythms. Can't bear to put your phone down? Dr. Malow suggests wearing glasses that block the blue light or setting your phone to night mode to improve sleep quality.
3. Exercise at the right time. "Regular exercise seems to increase the quantity of restorative slow-wave sleep," says Brendan P. Lucey, MD, director of sleep medicine at Washington University in St. Louis. But timing matters. "Particularly for vigorous exercise, it's important that you do it at least three hours before bedtime," says Dr. Lucey. High-intensity exercise raises heart rate and body temperature, which may increase wakefulness.
4. Walk more. Even low-impact exercise like walking can improve sleep, which is good news for people with neurologic conditions that might make vigorous workouts difficult. According to a 2019 study in Sleep Health, people who increased their daily step totals during a four-week period reported better sleep quality than usual.
5. Stay awake during the day. While a 20-minute power nap can improve alertness, anything longer may interfere with your ability to sleep at night. In a 2018 study by researchers at the University of California San Francisco (UCSF), men who napped for an hour a day were more likely to develop Parkinson's disease within an 11-year period. And a 2019 study in Alzheimer's & Dementia found that men who took long naps on a regular basis had a higher risk of developing cognitive impairment over 12 years. "Napping for two hours a day may end up being an early marker for preclinical cognitive impairment," says Yue Leng, PhD, assistant professor of psychiatry at UCSF's Weill Institute for Neurosciences and the lead author of the study. "Though we can't really say that napping is the cause—it's more likely a risk factor."
6. Alter your thinking. Cognitive behavioral therapy (CBT) can be an effective way to treat insomnia, according to a number of studies. "It goes beyond sleep hygiene," says Dr. Leng. "With CBT-Insomnia, or CBT-I, as it's known, we educate patients about good sleep habits but also teach them to change their behaviors with various techniques, including sleep restriction and stimulus control.