Sleep used to be viewed as a passive, dormant state – seemingly insignificant. But research begun in the 1950’s changed that. We now better understand that sleep affects our physical and mental health. Sleep is part of the circadian rhythm, a 24-hour cycle driven by light and dark in our environment. The circadian rhythm controls at least 15% of our DNA, including our body’s repair mechanisms. Most hormone production is regulated by sleep. The recently discovered glymphatic system works to eliminate toxins from the brain while we sleep. And sleep is when we solidify learning and establish memories.
When we don’t get enough sleep we are tired during the day, have concentration and memory problems, decreased attention span, and bad moods. Over time, health problems can develop. The immune system may weaken; obesity, diabetes and cardiovascular issues can develop due to sleep deprivation.
Sleep is a basic drive controlled by two systems:
- Sleep/wake homeostasis: the longer we are awake, the stronger the drive to sleep becomes; and
- Circadian rhythm: our internal clock that determines when we are alert and when we are sleepy.
Sleep occurs in a series of stages with varying brain wave activity, muscle tone and eye movements. Two major types of sleep are non-REM (or quiet) and REM (rapid eye movement) sleep. Non-REM, or N-REM, sleep includes both light and deep sleep. Most people have 4 or 5 cycles of sleep a night, with each cycle lasting about 90 minutes. Most of that time is spent in deep sleep (slow-wave) and dreaming (REM) sleep. Most deep sleep occurs in the first half of the night and most REM sleep occurs in the second half.
The quantity, quality and timing of sleep are all important.
Sleep: how much?
The sleep requirement is an individual one; genetics, heredity, age, health and activity level factor into determining how much sleep a person needs. Only you know how you feel when you open your eyes in the morning. If you feel drowsy during the day, you haven’t had enough sleep.
In Rosalind Cartwright’s The Twenty-Four Hour Mind we learn that the body’s internal body temperature drops in the middle of the afternoon. This “circadian slump” or “circadian dip” makes us feel sleepy enough to nap. If we get through this period without falling asleep and feel okay the rest of the day, we’ve had enough sleep.
Cartwright says we can determine how many hours of sleep we need by monitoring our unscheduled sleep. Often on weekends or while on vacation we go to bed later than we normally do and sleep later than we normally do. If you end up sleeping 2 or 3 hours more than usual under these conditions you’re probably not getting enough sleep regularly.
Sleep latency, the amount of time it takes to fall asleep, may be 10 to 20 minutes normally. People who fall asleep “before their head hits the pillow” or within 5 minutes of lying down may have sleep deprivation or even a sleep disorder (there is a difference – but that’s another blog post). Those who need an hour or more to fall asleep may be sleeping too much – the mind and body aren’t yet ready to settle down.
In 2015, after a major study, the National Sleep Foundation (NSF) revised its sleep duration recommendations:
Sleep: how well?
Some people don’t feel rested even though they report no problems falling asleep or staying asleep and even when they get enough sleep. The symptoms are the same as insomnia: drowsiness, low energy, poor memory/concentration, irritability, and moodiness. This non-restorative sleep may result from a lack of slow-wave sleep; it’s slow wave sleep that resets the brain so it’s ready for the new day.
As we age and our body chemistry changes, we spend less time in deep sleep and more time in light sleep. Sounds or lights awaken us more easily. Hormone production can be reduced. Our circadian rhythm can speed up so we get sleepy earlier in the evenings and we wake earlier in the mornings.
Our sleep requirements may not change that much, but our sleep patterns change. With age, sleep becomes fragmented and we get less REM time. Some researchers believe it’s the early sleep stages that are essential for our physical well-being and REM sleep is essential for our mental well-being.
Sleep you get before midnight may be the most important. Most of the recharging work the body does occurs between the hours of 11 pm and 1 am. The adrenal system is particularly active then. The gallbladder rids itself of toxins at this time; if you are awake those toxins may end up in your liver according to Dr. Joseph Mercola. He suggests that nature intended us to go to bed shortly after sundown, just as most animals naturally do.
Larks vs owls
There is a gene called Period or PER that determines when we are predisposed to sleep and when to wake. Some people, called “larks,” are early risers and tire earlier in the day and others, called “owls,” find it hard to function early in the day and become more alert later on. Most people are somewhere in between larks and owls.
Short naps can help make up for a lack of sleep the night before. If you nap, try to do it before 3 pm; later naps can make it harder to fall asleep at night.
Limit your nap-time to 20-25 minutes. If you nap long enough to get into deep sleep you will feel drowsy when you get up. If that’s not long enough, then try for a 90-110 minute nap so you can go through a complete deep sleep cycle.
The “caffeine nap” is a quick way to find extra energy. Quickly drink a cup of lukewarm coffee and then sleep for 20 minutes. There’s enough light sleep to replenish you, and when you wake up the caffeine will be kicking in. The energy burst will last about 3 or 4 hours.
Just why we need sleep is uncertain. But one of the world’s leading sleep researchers, Dr. Peretz Lavie, says we can live longer without food than we can without sleep.
We need food. We need water. We need sleep.
Adult Sleep Needs at Every Age: From Young Adults to the Elderly. (n.d.). Retrieved from http://www.webmd.com/sleep-disorders/features/adult-sleep-needs-and-habits
Brain may flush out toxins during sleep | National Institutes of Health (NIH). (n.d.). Retrieved from http://www.nih.gov/news-events/news-releases/brain-may-flush-out-toxins-during-sleep
Breus, M. (Director). (n.d.). Good night with the sleep doctor [DVD].
Cartwright, R. D. (2010). The twenty-four hour mind: The role of sleep and dreaming in our emotional lives. Oxford: Oxford University Press.
Epstein, L. J., & Mardon, S. (2007). The Harvard Medical School guide to a good night’s sleep. New York: McGraw-Hill.
Goldman, B., Klatz, R., & Berger, L. (1999). Brain fitness: Anti-aging strategies for achieving super mind power. New York: Doubleday.
Is Oversleeping Hazardous To Your Health? (n.d.). Retrieved from http://articles.mercola.com/sites/articles/archive/2008/11/08/how-much-sleep-do-you-really-need.aspx
Lewis, P. A. (2013). The secret world of sleep: The surprising science of the mind at rest.
Stevenson, S. (2016). Sleep smarter: 21 essential strategies to sleep your way to a better body, better health, and bigger success. New York, NY: Rodale.