For some people, the slightest noise awakens them at night. For others, the wailing siren of a passing fire truck doesn’t disturb their slumber. Just why, though, remains a bit of a mystery.
Although many people are self-proclaimed light sleepers or heavy sleepers, researchers have found that little is actually known about why people react differently to noises and other stimuli during sleep.
Genetics, lifestyle choices, and undiagnosed sleep disorders may all play a role. In addition, some studies suggest that differences in brain wave activity during sleep may also make someone a light or deep sleeper.
But whichever category you’re in, one thing is certain: The quantity and quality of the sleep you get both play an important role in your health.
Everyone Should Cycle Through Light and Deep Sleep Each Night
During sleep, you alternate between cycles of REM (rapid eye movement) and NREM (non-rapid eye movement) that repeat about every 90 minutes. NREM sleep consists of three stages.
Stage one, or the phase between being awake and asleep, is considered light sleep. You’re most likely to wake up during this stage. Deeper sleep begins in stage two, as your breathing and heart rate become slower and your body temperature drops.
Stage three is the deepest and most restorative stage of sleep (it’s also called “slow-wave sleep”). Breathing further slows, muscles relax, and tissue growth and repair occur.
Next is REM sleep. During this stage, your eyes move rapidly from side to side. Your brain activity, heart rate, and blood pressure are similar to being awake, according to the Sleep Foundation. This is the stage of sleep when the most dreaming occurs, as well as important parts of the memory consolidation process.
In general, as people age, they spend less time in the slow-wave and REM stages of sleep and more time in the lighter stages, according to a review article.
But it’s also important to note that how much time someone spends in light or deep sleep over the course of a night can vary significantly from person to person and night to night. Also, the amount of deep sleep someone gets isn’t necessarily correlated to the amount of total sleep they get. Someone who gets eight hours of sleep a night, for instance, may not experience as much slow-wave, deep sleep as someone else who gets just six hours a night.
“There may be some overlap between what people subjectively feel about the depth of their sleep and what we find in the lab when measuring the different sleep stages,” says David Neubauer, MD, an associate professor of psychiatry and behavioral sciences at the Johns Hopkins University School of Medicine in Baltimore. “But it’s not necessarily the same thing.”
What Makes Someone a Restless Sleeper?
If someone is not feeling rested and thinks it’s because they are sleeping lightly, they should look at the factors that might contribute to their inability to achieve a deep sleep, says Dr. Neubauer. Things like drinking alcohol too close to bedtime or in large quantities can disrupt healthy and consistent sleep cycles, as can keeping an inconsistent sleep schedule, according to the Sleep Foundation. A doctor can recommend a sleep study in a sleep lab or an at-home sleep test to see if a sleep disorder could be to blame, Neubauer says.
Some sleep disorders, such as obstructive sleep apnea, may contribute to light sleep by causing you to awaken throughout the night, due to breathing irregularities.
But it’s worth noting that just because you feel like you’re a light sleeper doesn’t mean that you’re not actually getting the sleep you need. What’s more important is that you wake up feeling rested, which is a good indication that you’re getting the deep sleep you need, says Eric Landsness, MD, PhD, an assistant professor of neurology and sleep medicine at Washington University School of Medicine in St. Louis.
Neubauer adds that it’s hard to generalize about what makes some people light sleepers and others heavy sleepers. “It might be some sort of genetics, or it might be that some people have a greater degree of arousal over a 24-hour cycle,” he says.
In most cases, factors under your own control affect the quality of sleep you get. “There are lots of issues related to lifestyle, medications, alcohol, and caffeine that can lighten sleep,” Neubauer says. “People might also not be getting enough sleep because they’re not spending enough time in bed due to the choices they make.”
How to Get More Deep Sleep Whether You’re a Light or Heavy Sleeper
If you feel groggy during the day or find yourself falling asleep — or if you feel irritable, experience memory problems, or have a decrease in your attention span — you might not be getting enough sleep or enough quality sleep. To get to the root of the problem, try these remedies to help reset your sleep schedule, or talk to your doctor or consult a sleep expert if these tactics are still not helping.
To improve the quality of your sleep, the following may help:
- Have a set bedtime and a set wake time. Also, try to avoid staying up late and sleeping in on weekends, says Rajkumar Dasgupta, MD, a clinical associate professor of medicine at the University of Southern California’s Keck School of Medicine in Los Angeles. Staying up on weekends makes it difficult to go to sleep early on Sunday night, which then leads to fatigue the next day.
- Manage stress all day long. Higher levels of stress are associated with sleeping less, according to the American Psychological Association. And research suggests that there may be an underlying biological explanation as to why stress is more likely to disturb some people’s sleep. Meditation, whether before bedtime or even if you wake up during the night, can help.
- Avoid alcohol close to bedtime. It may do a good job of knocking you out in the short term, but it interferes with deep sleep, says Dr. Dasgupta. That’s because drinking before bedtime may cause disruptions to your sleep cycle as your liver enzymes metabolize alcohol, according to the Sleep Foundation.
- Turn off the TV, and keep electronic devices away from the bedroom. “Keep your cell phone out of the room, so a text won’t wake you up, especially if you’re a light sleeper,” Dr. Landsness says.
- Avoid screen time at least 30 minutes before bedtime. Unplugging an hour or more before your head hits the pillow is even better. The light from screens messes with sleep by discouraging the body from releasing melatonin, which is the hormone that signals to the body that it’s time to fall asleep. And engaging with tech devices, even if just to answer a couple of emails or watch a TV show, is more energizing than relaxing, and it leads to cognitive arousal.
- Wear an eye mask. This will block light that may be seeping into the room from the edges of your curtains. “Light sleepers are prone to light contamination. That tiny bit of light emanating from the streetlight outside could affect your sleep,” Landsness says. Research suggests that wearing an eye mask can help people sustain longer periods of REM sleep, and that it encourages elevated levels of melatonin.
- Use earplugs or noise-canceling earbuds. This will help drown out ambient noise, especially if your bedroom is facing a window that picks up traffic sounds from outside, Landsness says. You can also try a fan or a white-noise machine that can play soothing sounds to help you fall asleep. A study found that the gentle hum of these kinds of devices can help some people fall asleep faster.
- Watch what you eat close to bedtime. Try to avoid snacks packed with sugar, which could cause a sugar spike. Also avoid caffeine and nicotine, both of which are stimulants. And spicy, acidic foods may cause heartburn or acid reflux that can interfere with sleep, according to the Sleep Foundation.
- Drink plenty of water. While it’s important to cut down your water intake roughly an hour or two before bedtime, staying hydrated during the day will help your sleep quality that night.
Additional reporting by Katherine Lee and Carmen Chai.