Despite decades of research, scientists don’t understand exactly why we sleep and how it benefits us. The best guess is that it enables the brain and the rest of the central nervous system to work properly. The brain may need sleep to recover from the day’s work just as muscles do—“sore labour’s bath, balm of hurt minds,” as Shakespeare put it. There is growing evidence for sleep as the partner of memory: In particular, it appears to strengthen newly formed memories and weed out old ones. But accumulating research shows that sleep affects nearly every bodily system—and that poor sleep can harm your health in many ways.
What is “enough” sleep?
“Enough” is whatever makes you feel refreshed and alert the next day. Most adults do best with six to eight hours—but as many as nine or 10 hours or as few as five hours may be fine for some people. Though observational studies have linked routinely sleeping less than six hours a night to increased mortality—and six to eight hours to lower death rates—what that means for individuals is unclear.
How well you sleep is as important as how long. In 2017, an expert panel assembled by the National Sleep Foundation came up with four “objective components” of good-quality sleep for people up to age 65, based on an analysis of 277 studies. The panel included experts not only on sleep but also on neurology, geriatrics, biology, and human development.
- Falling asleep within 30 minutes of going to bed.
- Sleeping at least 85 percent of the time spent in bed.
- Waking no more than once per night for longer than five minutes.
- Being awake for less than a total of 20 minutes after initially falling asleep. That is, it’s okay to wake up briefly, say, five times. But only one of these wake-ups should be longer than five minutes.
For people over 65, the criteria are relaxed somewhat, since sleep patterns change with age. Thus, if they take longer to fall asleep (up to 60 minutes) and wake up more often (totaling up to 30 minutes after initially falling asleep), that can still be considered good-quality sleep.
What about the various sleep stages, such as REM and slow-wave sleep—how much of your night should optimally be spent in each of them? The expert panel could reach no consensus.
Risks of poor sleep
Chronic poor sleep can cause or contribute to many serious health problems. Notably, sleep helps support the immune system; one week of poor sleep can lower resistance to infections and impair wound healing. Studies have also strongly linked poor sleep to increased risk of hypertension, type 2 diabetes, stroke, heart attack, cognitive impairment, depression, anxiety disorders, and premature death, though such associations do not prove cause and effect.
Shorter (and longer) sleep can be the result of various health problems and can worsen pre-existing health problems, resulting in a vicious cycle. The risks posed by poor sleep are clearest when it is the result of obstructive sleep apnea.
There’s accumulating evidence linking poor sleep to increased calorie intake, weight gain, and obesity. One proposed mechanism is that poor sleep affects the appetite hormones ghrelin and leptin. It can also impair glucose tolerance and increase insulin resistance, which can lead to weight gain. Sleep deprivation tends to decrease people’s motivation to diet and exercise. Being awake longer also means more time to eat. And in another vicious cycle, weight gain contributes to the development of obesity, which in turn worsens sleep, particularly if it leads to sleep apnea.
Poor sleep can have adverse effects on the brain and central nervous system. Even one night with only a few hours of sleep can impair concentration, coordination, productivity, judgment, and emotional stability. Lack of sleep can also severely affect driving. In fact, according to Dr. Charles Czeisler, a well-known sleep researcher at Harvard Medical School, sleeping only four hours a night for five nights, on average, or five hours a night for a week can impair you as much as being awake for 24 hours—or being legally drunk. And having just one beer in that sleepy condition has the effect of a six-pack.
It’s no coincidence that poor sleep and impaired memory frequently accompany aging. A study from UC Berkeley, published in Nature Neuroscience, linked certain structural changes in the brains of people in their seventies with both reduced deep sleep and cognitive decline. It’s a double whammy—brain deterioration impairs memory, and the disrupted sleep only worsens matters. Not exactly good news for older people, but it suggests that finding ways to help them sleep better may help prevent some cognitive losses.
Steps for better sleep
If you are having trouble sleeping, the following steps may help:
- Limit alcohol. Don’t drink alcohol to help you sleep—it’s a false friend. It helps you fall asleep quickly and deepens sleep initially, but later disrupts sleep and causes middle-of-the-night wake-ups. Overall, alcohol produces unsettled sleep and alters sleep phases, notably inhibiting REM sleep. High doses of alcohol worsen sleep more in women, according to a study in Alcoholism: Clinical & Experimental Research, since women metabolize alcohol differently from men. In addition, alcohol’s effects on sleep tend to be worse in older people and in those with sleep problems. Alcohol also increases the severity of sleep apnea.
- Avoid or cut down on caffeine, especially in the late afternoon and evening. The stimulant effects of caffeine vary from person to person, depending on how rapidly they metabolize it, whether they consume it regularly or not, and other factors.
- Don’t smoke. Nicotine, like caffeine, is a stimulant and can disrupt sleep. What’s more, you may be awakened by nicotine withdrawal symptoms.
- Eliminate noise. Try earplugs or a “white noise” machine.
- Make your bedroom sleep-friendly. Put up darker shades. A sleep mask can help. Your bed, linens, and pillows should feel comfortable. Most people sleep better in a cool (but not cold) room. Have an extra blanket within reach for those 3 a.m. wake-ups. Turn your clock to the wall if you can’t help looking at the time and worrying. Make sure that pets are not disturbing your sleep.
- Set a regular time to go to bed and get up, and stick to it—even on weekends and when you are sleep-deprived.
- Don’t eat a large meal two to three hours before bedtime. A full stomach can be uncomfortable and can promote heartburn or reflux disease. If certain foods, such as spicy or fatty ones, seem to cause nighttime heartburn, don’t eat them in the evening.
- Drink less liquid after dinner, so the need to urinate does not wake you (older people may have to get up anyway).
- If you nap during the day, keep it to 30 minutes maximum, and try to nap before 3 p.m. Short naps can enhance brain function, energy, mood, and productivity. But for some people with insomnia, it’s best to avoid napping altogether.
- Exercise regularly—it can improve sleep, especially if you are older. But don’t work out strenuously close to bedtime.
- Relax and try to retreat from your problems before going to bed. Read, listen to music, knit, meditate, work a puzzle—anything you find soothing. Give yourself some wind-down time starting at least 30 minutes before bedtime.
- Use your bed only for sleep (and sex). You should associate your bed with sleep. The sight and feel of it should signal your brain that sleep is coming.
- Limit your use of devices with an LED backlit screen close to bedtime— that includes tablet computers, smartphones, e-books, and many flat-screen TVs. Such screens emit blue light, which can interfere with sleep by reducing melatonin production, thus increasing alertness. Use the device earlier, or at least dim it as much as possible. Many digital devices have a night mode setting that limits blue light exposure by shifting the colors of the display to the warmer end of the color spectrum.
- If you can’t sleep, get out of bed. After 20 to 40 minutes, get up and do something else until you start to feel sleepy.
- Be aware of how your bed partner’s problems affect your sleep. For instance, a bedmate who snores or thrashes around can disrupt your sleep. Menopausal hot flashes can spoil a night’s sleep for both partners. Until your partner can manage these issues, you might want to try separate beds or separate rooms if possible.
- If you’re losing sleep because of worry, stress, or grief, try to find ways to mitigate this effect. This may be easier said than done, of course. If self-help measures don’t suffice, consider seeing a mental health professional. Sometimes even a single consultation can make a big difference.
What your doctor can do
If you’ve been sleeping poorly for several weeks, talk to your health care provider. Most people never mention their sleep problems, and doctors don’t often ask.
The following conditions are leading disruptors of sleep, and good medical advice can help you deal with them: sleep apnea, chronic pain, illness (such as thyroid disorders), restless legs syndrome, nocturnal leg cramps, an enlarged prostate (leading to frequent trips to the bathroom), severe menopausal hot flashes, shift work, chronic depression or other psychiatric conditions, and taking medications that interfere with sleep.
If your problems persist, your health care provider should refer you to a board-certified sleep specialist, who will evaluate you and may have you undergo testing at home or at a sleep laboratory. Or you may be referred to a cognitive behavioral therapist, who may help you change behaviors that are interfering with your sleep.