By Alexandra I. Mot, PhD
Did you know we spend approximately one-third of our lives asleep? Yet few of us realize the vital importance of sleep for our health—both physical and mental. According to an Irish proverb, “A good laugh and a long sleep are the best cures in the doctor’s book.”1
Our bodies function by an internal clock, consisting of circadian rhythms that regulate many body functions throughout a 24-hour period. The most well-known circadian rhythm is the sleep–wake cycle.
Melatonin is a hormone that plays a key role in regulating the sleep–wake cycle.2 Produced in response to diminishing light levels at dusk, it causes a person to feel sleepy. During sleep, melatonin levels rise sharply and then start to drop by early morning. Exposure to daylight inhibits melatonin production, thus keeping us awake during the day.
Interestingly, melatonin has many health benefits beyond sleep regulation. It is an antioxidant, prevents cancer, delays aging, boosts immune function, and aids brain regeneration and neuroplasticity.3 Going to bed early enables the body to produce more melatonin during the night and thus provide these important benefits.4
Sleep can be divided into two phases: non-rapid eye movement (non-REM) sleep and rapid eye movement (REM) sleep.
During non-REM sleep, a person progresses through four stages of increasingly deep sleep. This is followed by REM sleep, also known as dream sleep, in which the eyes move rapidly in different directions (as the name implies). During the night, a person will usually go through four or five recurring cycles of non-REM sleep and dream sleep with each cycle lasting between 90 and 110 minutes.5
Each sleep phase has a different purpose. While non-REM sleep is important for rebuilding and repairing the body, dream sleep is important for learning and memory as well as mental and emotional health.6 It is during dream sleep that the brain processes thoughts and emotions we have experienced throughout the day.
The amount of time we spend in each sleep phase changes during the night. The first few sleep cycles each night contain relatively short dreaming periods and longer periods of non-REM sleep. As the night progresses, dreaming periods increase in length while non-REM periods decrease. By morning, most people spend nearly all of their sleep time dreaming.7
In this way, the rejuvenation of the body (non-REM sleep) is prioritized over the rejuvenation of the mind (dream sleep).8 When a person’s sleep is cut short, most of what is cut out is dream sleep, adversely impacting mental and emotional health.
Sleep deprivation is a common problem, with one in three American adults not getting enough sleep on a regular basis according to the Centers for Disease Control and Prevention.9 While sleep needs vary with age, the average adult needs seven to nine hours per night.10
The consequences of sleep deprivation can be very serious, leading to thousands of deaths each year from car accidents, medical errors, workplace accidents, and even catastrophic disasters (such as the Chernobyl disaster).11 Not getting enough sleep can be fatal.
One study found that getting only six hours of sleep per night for ten consecutive days was as detrimental to mental performance as one night of total sleep deprivation.12 To put this in perspective, one sleepless night is the cognitive equivalent of being legally drunk.
Sleep deprivation can also have a profound effect on our emotional wellbeing. Lack of sleep often leaves us feeling irritable, anxious, and short-tempered. This occurs because sleep deprivation weakens the ability of the region of the brain that handles reasoning—the prefrontal cortex—to control the emotional part—known as the amygdala.13 Sleep deprivation also causes the amygdala to go into overdrive, making us more impulsive and intensely reactive to situations.
Interestingly, women are more likely than men to experience emotional difficulties as a result of sleep deprivation.14 Women’s brains use more energy during the day, so they need more sleep to fully rejuvenate.
Insufficient dream sleep is also strongly linked with depression.15 In fact, depression is sometimes referred to as the “loss of one’s dreams.” Lack of sleep causes an increase in negative thinking, especially the repetition of the same negative thoughts over and over again.16
Dream sleep is particularly important for processing painful memories. One study found that prisoners of war who got adequate sleep both before and after the war were less likely to develop post-traumatic stress disorder (PTSD) or other mental health problems after the war.17 Likewise, soldiers were more likely to develop PTSD from the horrors of war if they had experienced insomnia beforehand.18 This is because insufficient sleep contributes to the retention of negative emotional memories.
Sleep deprivation has also been linked to dementia and Alzheimer's disease. A recent study found that even one sleepless night increased levels of tau—a protein that drives brain damage and cognitive decline in Alzheimer's disease—by over 50%.19
So how can we avoid these costly effects? Here are some practical tips to help you get a good night’s rest.
For further study, we suggest the following resource: Ministry of Healing.
“Sleep Matters: The Impact of Sleep on Health and Wellbeing,” Mental Health Foundation, 2011.
Alisa Paliano, “19 Surprising Health Benefits of Melatonin in 2020,” Nestmaven, nestmaven.com.
See Reference 2.
Neil Nedley, “The 8 Laws of Health, NEWSTART, R for Rest,” Video, Jul. 12, 2017.
See Reference 1.
“REM, Light, Deep: How Much of Each Stage of Sleep Are You Getting?” Fitbit, blog.fitbit.com, Sept. 19, 2018.
“What Happens During Sleep?” UPMC, upmc.com.
Rubin Naiman, “Dreamless: The Silent Epidemic of REM Sleep Loss,” Annals of the New York Academy of Sciences, Vol. 1406(1), 2017, pp. 77–85.
“1 in 3 Adults Don’t Get Enough Sleep,” Centers for Disease Control and Prevention, cdc.gov, Feb. 18, 2016.
Hirshkowitz, et al., “National Sleep Foundation’s Updated Sleep Duration Recommendations,” Sleep Health, Vol. 1(4), 2015, pp. 233–243.
Colten and Altevogt (editors), Sleep Disorders and Sleep Deprivation, Washington, DC: National Academies Press, 2006, ch. 4.
Claire Maldarelli, “How Many Hours of Sleep do You Actually Need?” Popular Science, popsci.com, 11, 2017.
Michael Breus, “How Sleep Deprivation Hurts Your Emotional Health,” The Sleep Doctor, thesleepdoctor.com, May 1, 2018.
See Reference 12.
See Reference 8.
See Reference 12.
Segovia, et al., “Sleep and Resilience,” Military Medicine, Vol. 178(2), 2013, pp. 196–201.
Holth, et al., “The Sleep-Wake Cycle Regulates Brain Interstitial Fluid Tau,” Science, vol. 363(6429), 2019, pp. 880–884.
Alexandra I. Mot lives in Göttingen, Germany, where she works as a research scientist specializing in neurodegenerative diseases.