What Is Light Sleep vs. Heavy Sleep, and How Can You Get What You Need?

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 brainwave activity during sleep may also make someone a light or heavy sleeper.

But whether you’re a light or heavy sleeper, one thing is certain: Both the quantity and the quality of sleep you get play an important role in your health.

Alternating Between the Stages of Light and Deep Sleep

During sleep, you alternate between cycles of REM (rapid eye movement) and NREM (non–rapid eye movement) that repeat about every 90 minutes. You spend about 75 percent of the night in NREM sleep, which consists of three stages of increasing relaxation. (1)

Stage one, or the phase between being awake and asleep, is considered light sleep. Deeper sleep begins in stage two, as your breathing and heart rate become regular and your body temperature drops.

Stage three is the deepest and most restorative stage of sleep, in which breathing slows, muscles relax, and tissue growth and repair occurs.

Next is REM sleep, which is when your eyes move rapidly from side to side while closed — hence the name. This is the stage when most of our dreaming happens, and your brain wave activity, heart rate, and blood pressure increase to levels that are close to what we have when we’re awake.

In general, young people spend more time in the deeper, heavier stages of sleep as they grow and develop. Older people spend less time in deep-sleep stages and are more likely to complain of being light sleepers.

But sleep experts say the difference between a light and heavy sleeper may be largely subjective. Someone who gets eight hours of sleep a night may not experience as much slow-wave, deep sleep as the person who gets six hours of sleep.

“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 and associate director of the Johns Hopkins Sleep Disorders Center in Baltimore. “But it’s not necessarily the same thing.”

Lack of Shut-eye and a Sleep Deficit Crisis

Many health experts are calling attention to what they see as a public health crisis today: major sleep deficit. Between busy schedules at work and home, and devices that constantly connect us to email and social media — and let us binge-watch our favorite shows — we are more sleep deprived than ever.

This can wreak havoc on our physical, mental, and emotional health, says Rajkumar Dasgupta, MD, assistant professor of clinical medicine at the University of Southern California’s Keck School of Medicine in Los Angeles and a spokesperson for the American Academy of Sleep Medicine.

Poor quality sleep has been associated with increased risk of developing an array of health problems, including diabetes, (2) cardiovascular disease, depression, (3) and even Alzheimer’s disease. And research into the causes and effects of not dreaming enough, which happens when you don't enter the deep stage of REM sleep, has found that our dream deprivation is contributing to illness and depression.

A comprehensive review published in August 2017 in the journal Annals of the New York Academy of Sciences, which was conducted by Rubin Naiman, PhD, a sleep and dream specialist at the University of Arizona Center for Integrative Medicine in Tucson, found that there is growing evidence linking REM and dreaming to things like immune function, storing long-term memory, and mood. (4)

People who get less REM sleep may even face a greater risk of developing dementia, according to a study published in September 2017 in the journal Neurology. (5)

REM is the most important sleep stage, says Dr. Dasgupta. “It helps with memory, cognition, immune system function, weight loss, and depression,” he says. “Deeper stages of sleep burn more calories because you’re active, like when you’re awake.”

Factors Contributing to Light and Disruptive Sleep

A small study published in the journal Current Biology suggested that differences in how sleeping people respond to noise may be related to levels of brain activity called sleep spindles. (6) The researchers found that people whose brains produced the most of these high-frequency sleep spindles were more likely to sleep through loud noises. But more research is needed to confirm the results.

If someone is not feeling rested and thinks it's because they are a light sleeper, they should look at the factors that might be contributing to the inability to achieve a deep sleep, says Dr. Neubauer. A doctor can recommend a sleep study in a sleep lab to see if a sleep disorder may be to blame.

Some sleep disorders, such as obstructive sleep apnea, may contribute to light sleep by causing awakenings throughout the night due to breathing irregularities.

Neubauer added 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, medication, 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.”

Healthy Sleep Habits You Can Try Right Now

If you feel groggy during the day or find yourself falling asleep — or if you feel irritable, experience memory problems, or a decrease in your attention span — you may not be getting enough sleep or, specifically, enough deep sleep. To get to the root of the problem, talk to your doctor or consult a sleep expert, and consider trying the following:

• Have a set bedtime and a set wake time, and try to avoid staying up late and sleeping in on weekends, suggests Dasgupta. Staying up on weekends makes it difficult to go to sleep early on Sunday night, which then leads to fatigue the next day.
• Try to 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 Dasgupta.
• Turn off the TV, your cellphone, and any other electronic devices at least 30 minutes before bedtime. Unplugging an hour or more before your head hits the pillow is even better. The gadgets that we all surround ourselves with are robbing us of sleep in various ways. (7) The light from screens messes with your body's production of melatonin, which is the hormone that regulates your sleep-wake cycle. 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 leads to cognitive arousal.
• Do something nonstimulating shortly before bedtime, like reading a book (preferably one that’s not electronic) or taking a warm bath.
• Don’t eat too close to bedtime, to avoid heartburn. Try to keep at least four hours between dinnertime and bedtime. And of course avoid having caffeine, including hidden sources of caffeine, like chocolate, before bed.
• Optimize your bedroom for peaceful sleep. Make sure the room isn’t too hot, and dim the lights. Keep work out of the bedroom so that it becomes a place where you only relax and rest.