Sleep

The Deleterious Effects of Sleep Deprivation

If you were to ask a person living in modern-day society if he has had a full uninterrupted eight-hour sleep last night, the chances that you would get a positive answer are quite low. To working people who are overwhelmed by responsibilities, enjoying the recommended 7-9 hours of quiet rest at night may even feel like a waste of time. Typically, when a person with a busy schedule is set on winning more time, sleep is the first component to be subtracted from the equation. Paradoxically, the opposite proves to be true, since epidemiological studies show a direct link between sleep habits and life expectancy. In other words, the longer you sleep, the longer you live. Having that in mind, maybe it’s time to rethink the value of a good night’s sleep.[1] 

The sleep-wake cycle is one of the many rhythmic patterns orchestrated by our 24-hour internal clock within the brain. More specifically, this clock is located in the suprachiasmatic nucleus in the hypothalamus. It dictates the rhythm of multiple physiological processes including sleep, eating, drinking, mood, metabolic rate and core body temperature. Although every human has this exact same machinery, there are significant differences between the peaks of activity from person to person. Based on these variations there are three main chronotypes – morning types (40% of the population) will have a peak of wakefulness in the early hours of the day, while evening types, which account for approximately 30% of the population, are more active in the late afternoon and prefer to fall asleep late at night. The remaining percentage of people fall somewhere in the middle. Whether you are a “morning lark” or a “night owl” is surprisingly determined by genetics and is not a conscious choice. Disregarding this fact, our modern work schedules tend to suit the morning types but have detrimental effects on the health of night owls. Since they can’t fall asleep early in the evening but need to wake up in the morning, they are bound to be chronically sleep deprived. Consequently, those people suffer from higher rates of depression, anxiety, diabetes, cancer, heart attack, and stroke. [2]

Besides drawing the short straw when it comes to genetically predetermined chronotypes, a person can also become sleep deprived as a result of stimulant abuse or sleep-related disorders such as insomnia or obstructive apnea. Whatever the reason, the consequences of sleep deprivation leave no part of the brain or body unharmed. The leading causes of disease and death in developed nations – heart disease, obesity, dementia, diabetes, and cancer—all have recognized causal links to a lack of sleep. In regard to cardiovascular health, research has shown that adults forty-five years or older who sleep fewer than six hours a night are 200 percent more likely to have a heart attack or stroke during their lifetime, as compared with those sleeping seven to eight hours a night. All the mechanisms by which lack of sleep damages the cardiovascular system lead to an overactive sympathetic nervous system. During deep sleep the brain sends a calming signal to the fight-or-flight system for long durations of the night. As a result, deep sleep prevents an escalation of this physiological stress that is associated with increased blood pressure, heart attack, heart failure, and stroke. This would explain why a lack of deep sleep has the opposite effect on cardiovascular health. [2]

In addition, sleeping less than seven or eight hours a night will increase your probability of gaining weight, or being obese, and significantly increases your likelihood of developing type 2 diabetes. One study examined small samples of tissues of healthy individuals who received only four hours of sleep for a period of six nights. The results showed that their cells had become 40% less responsive to insulin. To complement this effect, inadequate sleep decreases concentrations of the satiety-signaling hormone leptin and increases levels of the hunger hormone ghrelin, causing one to easily overeat. [3]

Another example of the deleterious effects of sleep loss is its impact on the immune system. A study examining healthy young men demonstrates that after a single night of four hours of sleep the numbers of natural killer cells circulating in the immune system plummet by 70%. Also, epidemiological studies have reported that nighttime shift work, and the disruption to sleep that it causes, up your odds of developing numerous different forms of cancer considerably. Having in mind that the natural killer cells are a critical part of our immune defense against arising cancer cells, the reduction in their activity after just one night of “bad sleep” could partly explain the higher cancer rates among shift workers. [2]

Sleep deprivation inflicts damage on the epigenome as well. Research indicates that insufficient sleep changes the activity of hundreds of genes – some of which get silenced while others are turned on. The genes that are expressed more after a lack of sleep include those linked to chronic inflammation, cellular stress, and various factors that cause cardiovascular disease. Among those that get turned off are genes that help maintain stable metabolism and optimal immune responses. [2]

There are three main epigenetic mechanisms by which gene expression is being regulated: DNA methylation, histone modifications and non-coding RNAs. Sleep loss affects the DNA methylation pattern in 51 genes, among which are genes involved in the circadian clock and in metabolism. Histone acetylation leads to the relaxation of chromatin structure which in turn facilitates gene transcription. Research has shown that sleep deprivation decreases histone acetylation. One example of an affected gene is the one that codes for the protein BDNF (brain derived neurotrophic factor), which plays a crucial role in learning and memory. Micro-RNAs which are a type of non-coding RNA also show altered expression in sleep deprived mice. Therefore, inadequate sleep causes changes to the epigenome through all three of these main regulatory mechanisms. [4] 

Matthew Walker, a professor of neuroscience and psychology, jokingly said in an interview that as a sleep scientist his only role was to put the data behind everything that your mother has told you. Perhaps we should listen more carefully to professor Walker and our mothers and finally get a good night’s sleep!

Author
Yoana Ivanova – Medical University, Sofia

Sources
[1] Francesco P. Cappuccio, MD, FRCP, Lanfranco D’Elia, MD, Pasquale Strazzullo, MD, and Michelle A. Miller, PhD Sleep Duration and All-Cause Mortality: A Systematic Review and Meta-Analysis of Prospective Studies. SLEEP 2010 
Link to the full article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2864873/ 

[2] Walker, Matthew. “Why We Sleep: Unlocking the Power of Sleep and Dreams”,  Scribner, 2017 [3] Eve Van Cauter, Karine Spiegel, Esra Tasali, and Rachel Leproult Metabolic consequences of sleep and sleep loss. Sleep Med. 2008 
Link to the full article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4444051/ 

[3] Eve Van Cauter, Karine Spiegel, Esra Tasali, and Rachel Leproult Metabolic consequences of sleep and sleep loss. Sleep Med. 2008 
Link to full article:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4444051/

[4] Marie E. Gaine, Snehajyoti Chatterjee, and Ted Abel Sleep Deprivation and the Epigenome. Front Neural Circuits. 2018 
Link to the full article:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5835037/

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