Everyone needs sleep, but getting enough isn't always easy. Many Americans regularly sleep less than the recommended amount, and everyone has the occasional sleepless night.
Whether it's a demanding job, school exams or a screaming baby, there are plenty of reasons why people may only sleep for four hours at night — but is four hours of sleep enough?
TODAY.com spoke to doctors bout what happens when you sleep for four hours a night, the health effects of sleep deprivation, and how to get more rest each night.
Is 4 hours of sleep enough?
No, four hours of sleep is not enough for the average person. The minimum amount of sleep recommended for adults by the American Academy of Sleep Medicine is seven hours.
These recommendations are based on large-scale population studies looking at how much sleep people need, Molly Atwood, Ph.D., assistant professor of psychiatry and behavioral sciences at Johns Hopkins Medicine, tells TODAY.com.
"Somewhere between seven to nine hours seems to be the sweet spot, but it really does depend on the person," says Atwood.
Certain people can sleep for six or so hours a night and they are completely fine, says Atwood, whereas other people may need a bit more than nine hours to feel rested.
However, for the vast majority of people, seven hours is the lower limit. That's because sleeping less than seven hours per night on a regular basis is associated with adverse health outcomes, according to a joint consensus from AASM and the Sleep Research Society.
There are very rare exceptions: people called “short-sleepers,” who can function well and don’t face any health consequences despite sleeping only four hours or less each night, Dr. Bhanu Kolla, a sleep physician and psychiatrist at the Mayo Clinic, tells TODAY.com.
Short-sleepers naturally have shorter sleep requirements, says Kolla, which is believed to be caused by a genetic mutation.
You cannot train the body to need less sleep, the experts emphasize.
Related: Is 5 hours of sleep enough at night?
At night, the body cycles through five stages which fall into two categories: rapid eye movement or REM sleep and non-REM sleep, TODAY.com previously reported. During the recommended seven hours of sleep, people go through about four or five cycles.
Since the REM stages typically occur during the second half of sleep, sleeping too little may not allow the body enough time to complete all the REM sleep cycles, per the National Sleep Foundation.
Routinely sleeping less than you need can lead to sleep deprivation, which has many health effects. But even one night of too little sleep can impact you the following day.
Short-term health effects of sleeping four hours
The day after sleeping for four hours, you'll likely experience a few different changes.
Cognitive function
Deficits in reaction time and mental vigilance, or how well you’re able to maintain attention or focus, can pop up after too little sleep, says Atwood. These impairments can have implications for certain jobs, says Atwood — for example, operating vehicles.
Mood
In addition to feeling tired, it can be harder to regulate your emotions, says Atwood, and you may feel more irritable or anxious.
Coordination and motor skills
Losing too much sleep can also impair coordination and motor skills, Shelby Harris, Psy.D., a clinical psychologist specializing in behavioral sleep medicine and director of sleep health at Sleepopolis, tells TODAY.com.
“It can be considered similar to what a blood alcohol content would be for being legally drunk,” says Harris. The more sleep deprived, the greater the risk of falls and accidents, she adds.
Long-term health effects of sleeping four hours
While you can catch up from a night or two of poor sleep by resuming your routine for the next few nights, Atwood says, chronic sleep deprivation, lasting for months or years, can lead to "lasting health effects."
These include:
- Increase risk of diabetes, heart attack, stroke and kidney problems
- Increased risk of premature death
- Depression and anxiety
- Neurological disease, such as Alzheimer's
- Poorer quality of life
- In extreme cases, symptoms of psychosis
Why aren't people sleeping enough?
One-third of adults in the United States report that they usually get less than the recommended amount of sleep, according to the U.S. Centers for Disease Control.
Constraints like work, school and raising children, as well as lifestyle choices and poor sleep hygiene, are common reasons people do not sleep enough, Harris notes.
Health conditions and sleep disorders, such as insomnia or sleep apnea, can also disrupt sleep duration and quality.
“The proportion of people who do report sleeping six hours or less (on average) seems to be increasing over time,” says Atwood.
What’s the recommended amount of sleep?
Humans need different amounts of sleep during different stages of life, but individual sleep needs will vary slightly based on genetics, health, behavior and environment.
The American Academy of Sleep Medicine recommends the following amount of sleep for each age group:
- Infants (4–12 months old): 12–16 hours, including naps
- Toddlers (1–2 years old): 11–14 hours, including naps
- Young children (3–5 years old): 10–13 hours, including naps
- School-age children (6–12 years old): 9–12 hours
- Teenagers (13–18 years old): 8–10 hours
- Adults (18 or more years old) need 7 or more hours
How do you know if you're sleeping enough?
If you are sleeping within the recommended range, wake up feeling rested and don't experience excessive daytime sleepiness, you're probably sleeping enough, the experts note.
Most people feel a bit groggy for about 30 minutes after waking up. “Some fatigue during the day is normal. ... In the afternoon, everybody hits a slump,” says Atwood. However, if you're feeling drowsy or fatigued and dozing off the entire day, "that's a pretty good sign that you're sleep deprived."
If you sleep significantly more on the weekends relative to how long you sleep on weekdays, it may be a sign you are sleep deprived during the week, Atwood adds.
How to get more sleep
Prioritizing sleep is not always easy. The experts recommend the following steps:
Develop a wind-down routine.
It's important to make sure your body is physically and mentally ready for sleep, the experts note. "If you're tense or anxious, it kicks in the fight-or-flight response, which is designed to override sleep," says Atwood.
Try to wrap up the day and avoid worrying, planning or problem-solving once you're in bed. "Make sure that you've had some time to wind down and relax, however you accomplish that," says Atwood.
Creating a dark, quiet, cool and comfortable sleeping environment can also help.
Go to bed and wake up at the same time.
Consistency is key, the experts note, which means going to sleep at or around the same time every night.
"Waking up at the same time every day is also super important so you can start building up that pressure for the next night of sleep," says Atwood.
Avoid screens before bedtime
"Sleep is regulated by the circadian rhythm, which is like our internal sleep-wake clock," says Atwood. At night, when it's dark, the brain releases melatonin, which is a cue to shut down and sleep.
Any light, including light from screens, can inhibit the release of melatonin, keeping you awake for longer. It's common for people to turn off overhead lights and stay on their phones or laptops, but these can still keep you awake, Atwood notes.
Avoiding screens for at least an hour can allow melatonin to get released so it's easier to fall asleep, says Atwood.
Limit caffeine and alcohol
Caffeine lingers in your system for about eight hours, says Atwood. If you're drinking it too late, or you're drinking too much, it can make it harder to fall asleep. Try to limit caffeine intake if possible, or stick to a cutoff time so it has time to wear off.
Alcohol can also disrupt the quantity and quality of sleep, the experts note, so people should avoid drinking excessively or too close to bedtime.
Eating a balanced, nutritious diet and exercising regularly can also promote sleep health, the experts note.
If you are concerned about your sleeping habits, talk to a doctor.