For years, public health messages have stressed the importance of diet and physical activity. Now, the sleep-deprived American public is learning (the hard way) that sleep is a critical third pillar of a healthy lifestyle.
Increasingly, scientists are discovering that how much and how well you sleep throughout adulthood can be a big factor in how healthy you stay into your golden years. Insufficient sleep increases the risk of disorders, such as high blood pressure, diabetes, obesity, stroke and depression. It's also associated with cognitive decline and Alzheimer's disease.
"We see very large changes to sleep physiology with aging," says Michael Scullin, PhD, an assistant professor of psychology and neuroscience at Baylor University who studies sleep neuroscience and cognition. "Those changes might be a contributing factor to some of the changes we see in general health, cognition and mental health as people age."
Quantity and quality
Many discussions of sleep are centered around how many hours a person clocks each night. "We have 50 years of data showing that people who sleep between seven and eight hours live the longest. That relationship doesn't seem to change too much with age," says psychologist Michael Grandner, PhD, director of the Sleep and Health Research Program at the University of Arizona.
But the quality of the sleep you get is just as important as the quantity, if not more so, sleep experts say. "Lower-quality sleep is associated with cognitive problems, as well as a whole host of physical problems," says Thomas Neylan, MD, a professor of psychiatry at the University of California, San Francisco, who studies sleep's role in metabolic health, cognitive function and neurodegenerative disorders.
Mounting evidence suggests that poor sleep fuels inflammation, which can lead to a variety of diseases including obesity, diabetes, heart disease and some cancers. Martica Hall, PhD, and colleagues followed older adults and found those who reported regularly getting less than six hours or more than eight hours of sleep per night had more inflammatory markers in their blood. That increased inflammation was associated with a greater mortality risk, particularly in those who were short on sleep (Sleep, Vol. 38, No. 2, 2015).
Scientists are still sorting out why sleeping too much is problematic. Too much sleep, like too little, appears to increase the risk of some diseases. But in many cases, excess slumber is probably a side effect of other medical problems, rather than a cause. Sleep disorders such as sleep apnea, for instance, can disrupt sleep cycles and leave people drowsy after a full night of sleep.
Unfortunately, getting quality sleep can become more difficult as people age. In one older but notable national survey, Daniel J. Foley and colleagues at the National Institute on Aging found that more than 50 percent of older adults complained of having sleeping difficulty, and that their sleep troubles were often associated with health problems (Sleep, Vol. 18, No. 6, 1995).
Older adults are more likely to have pain or illnesses that interrupt sleep and often find themselves waking more often to use the bathroom. Some medications cause agitation, restless legs or other side effects that can keep people up at night. Such difficulties can cut into the time older adults spend in deep sleep, when the body repairs tissues, shores up its immune function and processes memories.
Some sleep disorders also become more common later in life. Though prevalence estimates vary, there's evidence that both insomnia and obstructive sleep apnea become more common in older age, Grandner notes.
But even healthy older adults without sleep disorders can expect their sleep patterns to change over time. And those changes might lead to slumber that's not as restorative as it could be.
One notable change involves deep sleep, also referred to as slow-wave sleep. Deep sleep immediately follows the initial light stages of sleep from which people can wake easily. It is characterized by patterns of electrical activity in the brain known as slow waves, as well as faster bursts of brain activity called sleep spindles.
Both slow waves and sleep spindles play a role in transferring memories from the hippocampus to the prefrontal cortex and consolidating them for long-term storage. In addition to memory, slow waves have been tied to attention, cardiovascular health and metabolic regulation, says Bryce Mander, PhD, an assistant professor at the University of California, Irvine, who reviewed the neuroscience of sleep with colleagues from the University of California, Berkeley (Neuron, Vol. 94, No. 1, 2017). And sleep spindles are also thought to be important for healthy cognition, he adds.
Research shows that beginning in middle age, people spend more time in light sleep at the expense of that recuperative deep slumber. Both the amplitude and the density of slow waves are reduced. "That decline continues to progress across the lifespan to the point where older adults might be getting less than half of the slow-wave sleep they had when they were young adults," says Mander.
Many older adults also experience a shift of their natural sleep rhythms, says Colin Espie, PhD, a professor of sleep medicine at the University of Oxford. "There's an aging of the circadian clock." Older adults' tend to become sleepier earlier in the evening and wake earlier in the morning—the opposite of the circadian cycle that keeps teenagers awake late into the night.
Circadian changes can also contribute to older adults' feeling drowsy during daylight and alert in the wee hours, Espie says. While those circadian changes seem to happen as a normal consequence of healthy aging, they are more pronounced in people with dementia, he adds.
Slumber and the brain
Sleep is critical for cognitive function in the short term. Lack of sleep can impair attention, working memory, reaction time and executive function (and wreak havoc on your mood).
But regularly skimping on sleep in midlife can have cumulative impacts, too. After analyzing published studies, Scullin and Donald Bliwise, PhD, at Emory University, concluded that maintaining good sleep quality in young adulthood and middle age is likely to protect against age-related decline in later years (Perspectives in Psychological Science, Vol. 10, No. 1, 2015).
Other research has focused on the role sleep might play in protecting the brain from Alzheimer's disease and related forms of cognitive impairment. Sleep problems are well documented among people with the disorder. They tend to nod off during the day and wake numerous times during the night, says Neylan. "The ability to have sustained periods of wakefulness and sleep appears to be broken down."
Impaired sleep is so common among people with Alzheimer's that researchers are now exploring whether disordered sleep patterns could be an early indicator of the disease.
There is also mounting evidence that the sleep-Alzheimer's link runs both ways. In other words, it's not just that Alzheimer's disease impairs the structure of healthy sleep. Sleeping poorly over the course of the lifespan could also increase the risk for cognitive decline and Alzheimer's disease. Ricardo S. Osorio, MD, at New York University School of Medicine, and colleagues have shown that sleep-disordered breathing such as apnea is associated with an earlier average age for the onset of cognitive impairment (Neurology, Vol. 84, No. 19, 2015). And in a systematic review of more than two dozen studies, Omonigho Bubu, MD, and colleagues found that sleep problems could account for about 15 percent of Alzheimer's disease cases in the population (Sleep, Vol. 40, No. 1, 2017)—a noteworthy number, given that the disease affects approximately five million Americans.
The mechanisms for that association aren't entirely clear, though the chronic inflammation associated with poor sleep could certainly damage neurons, Neylan says. There is also emerging evidence to suggest that sleep has a role in clearing the beta-amyloid proteins that clump together in the brains of people with Alzheimer's disease.
Much of that evidence comes from David Holtzman, MD, at Washington University in St. Louis, and colleagues, who found that beta-amyloid plaques accumulate more quickly in the brains of mice that have been chronically sleep deprived (Science, Vol. 326, No. 5955, 2009).
More recently, Holtzman's team showed that one night of poor sleep can affect beta-amyloid levels in people. They recruited participants to spend a night in the lab and disrupted the sleep of half the participants with a series of loud beeps each time they sank into slow-wave sleep. The next day, the team found those who had disrupted sleep had 10 percent higher levels of beta-amyloid protein in the fluid surrounding their brains and spinal cords (Brain, Vol. 140, No. 8, 2017).
Research from Maiken Nedergaard, MD, at the University of Rochester, and colleagues suggests one possible mechanism for that connection. They've discovered that deep sleep causes glial cells in the brain to shrink. That, in turn, opens up pathways for fluid exchange that flushes away waste products such as beta-amyloid (Science, Vol. 342, No. 6156, 2013). "Sleep is part of the plumbing system of the brain," Neylan notes.
Enter sandman: Improving sleep
Such dramatic changes aren't likely to result from a few nights of tossing and turning, however. Most sleep researchers suspect that when it comes to healthy aging, long-term sleep patterns across young adulthood and middle age might be what matter most. "By the time you're 70, whether or not you have hypertension or Alzheimer's disease is probably not really dictated by how you slept in the last two weeks. It probably has more to do with how you slept 20 years ago," says Grandner.
And just as you wouldn't expect to counteract a lifetime of bad habits by beginning to eat well and exercise in your 80s, sleep hygiene should be a priority at every age. That involves establishing healthy sleep habits such as avoiding late-day caffeine, limiting afternoon naps, skipping out on late-night screen time and being exposed to natural light patterns.
However, truly disordered sleep requires intervention beyond those basic habits, Grander says. "Sleep hygiene is something everyone should do, but you have to remember: Hygiene isn't treatment," he says. Some disorders, such as sleep apnea, are readily treatable with devices or surgeries to open the airways. Insomnia is also treatable—but there's no quick fix.
Prescription and over-the-counter sleep aids can be tempting to people tossing and turning all night, but they aren't a substitute for natural shut-eye. Sleeping pills do not induce normal patterns of restorative sleep, Mander says.
That's one reason why the American College of Physicians recommends cognitivebehavioral therapy for insomnia, known as CBT-I, as first-line treatment rather than sleeping pills, Espie says. Insomnia often develops out of a short-term sleep disturbance. "Then people get stuck. The worse insomnia gets, the more they worry about it," he says. "This is precisely why CBT-I is effective at resolving insomnia. It allows people to address this vicious cycle," he says.
Most psychologists aren't specifically trained in this form of CBT. However, it's not much of a stretch for clinicians who are trained in cognitive and behavioral techniques to get up to speed on CBT-I, he says.
"Across psychological interventions, there's a lot of common ground in terms of methodology," Espie says. "Although the techniques may be unfamiliar, they are all based in cognitive and behavioral principles. Once people learn to use them, it makes a lot of sense." (See a list of training opportunities for CBT-I at www.apa.org/monitor/2016/10/insomnia.aspx.)
Healthy sleep behaviors
Psychologists can help promote healthy sleep in other ways as well, such as by encouraging clients to recognize how insufficient or troubled sleep might be affecting them. "A lot of individuals who sleep poorly don't recognize how much their poor sleep is negatively affecting them," Scullin says.
In one notable example, Hans Van Dongen, PhD, now at Washington State University, and colleagues showed that after two weeks of being forced to cut back to just six hours of sleep per night, participants' cognitive function suffered—though they generally believed they'd adapted to the shorter sleep and didn't realize how much it changed their performance (Sleep, Vol. 26, No. 2, 2003). "When clinical psychologists encounter people who say they are sleeping poorly, but doing OK, I'd recommend a little dose of skepticism," Scullin adds.
Behavioral health experts can also research better ways to encourage people to adopt healthy nighttime behaviors, Grandner says. "Meeting the biological need for sleep is driven by choices, beliefs, attitudes, opportunities—all of the things that health psychologists have been talking about for ages. But sleep hasn't really been on their radar as much," he says.
Still, it's too soon to declare sleep a cure-all, Mander stresses. More longitudinal studies are needed to determine whether specific sleep interventions will translate to fewer cases of Alzheimer's and other diseases associated with aging. "There's a lot of interest in thinking about how sleep interventions may play a role for improving cognitive or physical health in aging, but we just don't know enough yet," he says.
On the other hand, there's no downside to making sure you consistently get a good night's rest, no matter what age you are. "There isn't a single organ system in the body that isn't affected detrimentally by sleep loss," Mander says. "If you disrupt sleep, you disrupt function everywhere. But if you can improve sleep, you might have a chance of improving everything."
Sleep and Human Aging
Mander, B.A., Winer, J.R., & Walker, M.P. Neuron, 2017
Sleep: A Novel Mechanistic Pathway, Biomarker, and Treatment Target in the Pathology of Alzheimer's Disease?
Mander, B.A., et al. Trends in Neurosciences, 2016
Cognitive Behavioral Therapy for Insomnia Comorbid With Psychiatric and Medical Conditions: A Meta-analysis
Wu, J.Q., Appleman, E.R., Salazar, M.A., & Ong, J.C. JAMA Internal Medicine, 2015
Sleep, Cognition, and Normal Aging: Integrating a Half-Century of Multidisciplinary Research
Scullin, M.K., & Bliwise, D.L. Perspectives in Psychological Science, 2015
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