The effects of sleep deprivation (SD) have been studied for over a century and are not only limited to cognitive deficits but whole body deterioration as well. Research has shown that the body reacts to sleep deprivation by affecting gene expression, cellular responses in organs and tissues, and overall homeostatic balance. These result in leaving the body with a greatly increased chance for contracting life threatening illnesses. Many studies have been done on animals and humans to further gain a deeper understanding to the many biological effects caused by sleep deprivation. The Center for Disease Control conducted a census for the United States population concerning sleep duration, which showed that 34.9% to 35.5% of adults over the age of 18 in 2014 slept less than 7 hours a night (Sleep-CDC, 2017). This means that a little over a third of Americans are in a state of chronic sleep deprivation.
To understand sleep deprivation and its effects, the basic concept of the sleep cycle and what occurs throughout it must be understood. There are four stages of non rapid eye movement (NREM) sleep followed by one stage of rapid eye movement (REM) sleep totals to five total necessary stages of sleep. The brain’s neuron ability to integrate new memories into long term memories is primarily done in the NREM stages. According to the National Sleep Foundation, during the fourth NREM stage, known as the restorative stage, …the body repairs muscles and tissues, stimulates growth and development, boosts immune function, and builds up energy for the next day (Robbins, 2015). The REM stage of sleep contributes mostly to brain consolidation and information processing, which in turn contributes to learning and memory operations. Two internal biological processes work together to regulate sleep and wake states. They are known as circadian rhythm and sleep-wake homeostasis. Circadian rhythm impacts hormone release, body temperature, digestion, and sleep cycles among other functions. Sleep-wake homeostasis regulates the body’s primal need for sleep by adjusting substances such as adenosine that build up in the cerebrospinal fluid, and that increases with each hour a person is awake, only to be alleviated to lower levels when sleeping takes place (2).
Researchers who conducted a review on the neurobiological consequences of sleep deprivation covered a plethora of issues as sleep deprivation relates to brain function, learning and memory, neurogenesis, inflammatory responses, and cognition related signaling molecules. On the review of brain function as well as learning and memory, past research has shown that as the body continually seeks to reinstate homeostasis by attempting to sleep during forced consciousness, the stress to the system becomes an allostatic load. (Alkadhi, 2013) This is a negative physiological ramification of repeated exposure to stress on the body, causing damage to the various systems within. The allostatic load can cause a modification in the location of the set point for the engagement of homeostasis. When this point is not where it should be, the structural and functional brain regions that are involved in memory can be altered. An allostatic load exposed to the body for a long period of time can lead to bodily breakdown and disease resulting in diabetes, cardiovascular disease, and other illnesses (Alkadhi, 2013).
Sleep deprivation inhibits neurogenesis and the brain derived neurotrophic factor (BDNF) by the stress it projects onto the body’s system and brain. BDNF is a protein produced in nerve cells and is one of the most active neurotrophins that stimulate and control neurogenesis, cognition, and neuronal plasticity. Cognition deficits exacerbate the brain’s abilities for mood regulation, which leads to anxiety, depression, and anger. Compromises in immune system function have also been found in sleep deprived individuals. Not only is the body’s immune system subject to suppression, resulting in decreased ability to fight off bacterial attacks, but findings also show elevations in cytokine secretions resulting in an increased inflammatory response throughout the body. A study done on measuring the levels of cellular and genomic markers of inflammation related to increased cytokine responses of sleep deprived individuals by several renowned scholars has shown a 3-fold increase in transcription of interleukin 6 messenger RNA and a 2-fold increase in tumor necrosis factor ?± messenger RNA (Irwin et al, 2006). Their findings proved that sleep loss altered the molecular activities that propel cellular immune initiation and induced inflammatory cytokines. Unregulated inflammatory mechanisms can greatly increase risk for cancer, cardiovascular disease, diabetes, arthritis, and metabolic and neurodegenerative diseases.
Endocrine organs that are affected by sleep deprivation experience increases and decreases in hormones that help regulate the body. The thyroid stimulating hormone that regulates metabolism decreases while levels of the human growth hormone increase. These high levels of HGH impact glucose tolerance and lead to anti-insulin effects where the body has issues absorbing glucose in the blood. The pituitary gland releases hormones that direct the release of other hormones from the peripheral endocrine glands. This ability is greatly influenced by sleep where pituitary dependent hormones react to sleep deprivation by increasing cortisol and promoting insulin resistance. During the absence of sleep, the body decreases leptin, the appetite suppressing hormone, and increases ghrelin, a hormone that stimulates appetite. These unregulated hormones lead to the risk of obesity and diabetes.
Sleep deprivation alters gene expression in numerous areas in the body. There are two major steps in gene expression. One is transcription, which is the process of copying DNA to make RNA. The other process is translation, which is the process of interpreting the RNA into proteins to perform other functions within the cell. Eryn Brown reviewed a recent study done by genomist, Colin Smith, on gene expression and sleep deprivation, it was found that a total of 711 genes were affected by SD in the encoding process. These genes had changes in their rhythmic patterns of ‘on and off timing’ meaning that their normal activity was either intensified or reduced. About 444 genes were turned down while 267 were amped up. Resulting in an unbalanced regulation and ultimately an alteration of genes (Brown, 2013). Findings showed that the majority of the genes affected were involved in metabolism, gene regulation, stress responses, and regulating sleep homeostasis. When ‘gene regulating’ genes are affected, a domino effect is created causing numerous negative changes in many areas of the body.
In conclusion, sleep is a crucial component for the body for various reasons. Sleep is critical for restoring homeostasis within the body. Once sleep deprivation takes place, the body undergoes a severe stress reaction that it continually seeks to overthrow. Internal systems start to malfunction and an absence of necessary activities within the body start causing damage. This damage can include issues regarding hormone release that affect appetite, disruptions in the sleep cycle, negative immune responses, and difficulties in brain function, and altering gene expression regulations within the body. Sleep is also very important for information processing and the consolidation of memories. The body needs to go through the stages of NREM and REM sleep to initiate neuronal activity and repair for muscles and tissues in the body, as well as to regulate various hormones that affect digestion, blood glucose levels, inflammatory responses, and cognition stimulation. Cardiovascular, neurodegenerative, and metabolic diseases can also affect the body if equilibrium is not reinstated. Risk for cancer, arthritis, and severe mood changes are more prominent for sleep deprived individuals as well. Changes on a cellular level make the concept of sleep deprivation more complicated than just feeling tired. The different systems within the body continually fight for stability and when the fight is lost and sleep is continually prevented, alterations throughout the body take place. Therefore, sleep is a vital component in keeping the intricate inner workings of the body in proper functioning order.
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