by Evon Cheong
As a medical student, I find myself fascinated by the depth and breadth of science and how it is so intrinsically intertwined with our daily lives. Recently, we learned about the physiology of sleep and the extremely significant role it plays in safeguarding our health. It was then that I asked myself: How much care and attention do we really pay to the basic things that contribute to our well-being? Given how important sleep is, why is it one of the first things we are always willing to sacrifice in our tenacity to fill the fissures of our lives with accomplishments and experiences?
Perhaps it is due to our conjured perception that one or two hours of sleep deprivation can do no harm. However, the reality is that even a small amount of sleep deprivation can be detrimental. According to Dr. Charles A. Czeisler, the Baldino Professor of Sleep Medicine at Harvard Medical School, “If humans average four hours of sleep a night for four or five days, they develop the same level of cognitive impairment as if they’d been awake for 24 hours ‒ equivalent to legal drunkenness. Within ten days, the level of impairment is the same as you’d have going 48 hours without sleep. This greatly lengthens reaction time, impedes judgment, and interferes with problem solving.”1 Table 1 shows the amount of sleep that we need based on age.
PHYSIOLOGY OF SLEEP
To appreciate the significance of sleep, it is essential to review its underlying physiology. For centuries, sleep has been misperceived as an inactive state. In 1929, electroencephalogram was invented to enable scientists to record the electrical activity of the brain. Since then, it was proven that sleep is a dynamic process, and our brain is hard at work while we are sleeping. Sleep is divided into two key phases ‒ rapid-eye-movement (REM) and non–rapid-eye movement (NREM) sleep. Sleep begins with the NREM state. NREM sleep is further divided into four stages of sleep: onset (Stage 1), light sleep (Stage 2), and deep sleep (Stages 3 and 4). After about 60 to 90 minutes, REM sleep sets in (Stage 5), lasting for approximately 20 to 30 minutes. Subsequently, NREM sleep returns to start a new sleep cycle. A healthy adult goes through four to six consecutive sleep cycles in one night. Illustration on the next page shows the stages of sleep in an adult.
BENEFITS OF HAVING SUFFICIENT SLEEP
Sleep plays an important role in the consolidation of memory, which is pivotal for learning new information. Research suggests that memory consolidation takes place during sleep via the strengthening of the neural connections that form our memory2. It has long been known that a good night’s sleep reinforces the day’s memories, transferring them from short-term storage into longterm holding. However, it is helpful only if you explicitly tell yourself you’ll need the information in the future. In other words, don’t expect eight hours of shut-eye to help you on a pop quiz.Using EEGs, scientists at the University of Lübeck in Germany found that the “test is coming” group spent more time in deep sleep than did the group not anticipating a test. Slow electrical waves act as a replay button, causing the hippocampus to reactivate new memories and synchronizing the neocortex so that the memories are stored in the long-term memory bank. This expectant group also had more “sleep spindles,” bursts of electrical activity that prime networks in the cortex to store memories arriving from the hippocampus and to integrate
them into existing knowledge, facilitating retrieval3.
There are several repercussions of not getting sufficient sleep. Sleep deprivation slows our metabolism and raises our cortisol level. Cortisol is a stress hormone that increases our cravings for foods high in fat and carbohydrate. Increased level of cortisol is linked to insulin resistance, a risk factor for both diabetes and obesity. When we are sleep-deprived, our body produces more ghrelin, the hormone which increases hunger, and less of the hormone leptin, which helps prevents overeating. Plus, those who are not getting at least seven hours of sleep every night are losing precious REM sleep, the stage where you burn the most calories4.
The effects of sleep deprivation may not be immediate, but think about the tragic road accidents
caused by drivers who fall asleep at the wheel. The causal link between sleep deprivation and mortality is real. Since sleep deprivation alters immune function, including the activity of the body’s natural killer cells, and may eventually cause a string of diseases, having sufficient sleep may also help fight cancer and keep us healthy5. Dr. Mehmet Oz (cardiothoracic surgeon, television personality and author based in the US) has recommended the following for better sleep6.
Considering how important sleep is, sleep should no longer be deemed as an expendable luxury.
It is an integral part of our lives and an easy way to keep us healthy and whole!
“Thus God saves his loved ones from dread and alarms,
While safely they sleep in his own loving arms;
Rest here and hereafter he richly imparts
To all who permit him to dwell in their hearts.
Sweet sleep, richest boon to the wearied one given,
Little halts to take rest on the march up to heaven” – Sleep, a poem by S. Moore7
ABOUT THE AUTHOR:
Cheong E Von is a medical undergraduate at University College Cork, Ireland. She can be contacted at [email protected]. Find out more by visiting her Scientific Malaysian profile at http://www.scientificmalaysian.com/members/cheongevon/
1. Fryer, B., 2006 Sleep Deficit: The Performance Killer, Harvard Business Review – The Magazine: http://goo.gl/0PqTI
2. Division of Sleep Medicine, Harvard Medical School, Sleep, Learning, and Memory: http://goo.gl/nk2H4
3. Begley, S., 2011.Sleep Your Way to an ‘A’, The Daily Beast – Newsweek Magazine: http://goo.gl/EgFJc
4. Oz, M., 2012. Dr. Oz’s 4-Step Weight Loss Plan You Can Do in Your Sleep: http://goo.gl/SF9Yi
5. Harvard Health Publications, 2006: http://goo.gl/YBTlJ