Diseases and Disorders

Chronic Sleep Insufficiency - an Epidemic

Sai Chandrasekhar


Abstract

Sleep is one of the most essential but often overlooked components of modern life. The importance of sleep can be understood from the fact that we spend about one-third of our lifespan sleeping. Sleep has been implicated in learning, memory, restoring body’s energy levels, performance and physical health. In order to prevent physiological changes that may predispose individuals to poor health outcomes, sleep of sufficient duration, continuity, and intensity (depth) without circadian disruption is necessary. Chronic sleep deprivation resulting in cumulative sleep debt is a health hazard that has been on the rise. This has been implicated in various disorders such as obesity, diabetes, cardiovascular disorders, stroke and memory loss. Sleep insufficiency is a rising epidemic and awareness about sleep disorders should be spread amongst adults and students.

 

    All of us require sleep, and we all know when we’re sleepy! Literature suggests that the average adult should get seven to nine hours of sleep daily. However, a large portion of the population regularly falls short of that requirement.  Sleep is a complex, universal, and reversible behavioral state in mammals that is homeostatically regulated with its primary function: providing rest and restoring the body's energy levels. Following the discovery of rapid eye movement (REM) sleep in 1953, researchers learned that there are three basic states of consciousness: wakefulness, REM sleep, and non-rapid eye movement (NREM) sleep. Human NREM sleep can be classified into four stages, namely, stage I, II, III and IV, representing successively deeper stages of sleep [1]. Further research showed that sleep is not a passive phenomenon as thought by some but an active process involving several brain areas, during which multiple areas in the brainstem and hypothalamus promote wakefulness by actively sending signals to the cerebral cortex (see below).

    An important area of the brain that promotes wakefulness is the tuberomammillary nucleus (TMN) that releases histamine as one of its neurotransmitters.  The ventrolateral preoptic area (VLPO) and other basal forebrain areas play a major role in the promotion of NREM sleep (see below) by shutting down the arousal centers {2].

    Interaction of the pedunculopontine and lateral dorsal tegmental areas with the dorsal raphae nucleus and locus coeruleus is important for REM sleep generation [3]. Furthermore, the circadian rhythm of sleep is controlled by the suprachiasmatic nucleus of the hypothalamus and the pineal gland. There is a ‘switch’ involved in the transition between these states that researchers call mutual inhibition. The areas of the brain that maintain wakefulness by activating the cortex simultaneously switch off the VLPO neurons. Conversely, when VLPO neurons fire rapidly and induce sleep, they also inhibit the arousal centers such as the TMN by inhibiting them [4].

 

    The body regulates sleep in two ways: those being by increasing the level of adenosine in circulation, and through stimulating the suprachiasmatic nucleus, which controls body rhythms. As the adenosine levels build-up in the basal forebrain areas, due to the cells’ activity over the day, the brain acts as a dimmer switch and turns down cognitive processes and responses [5].

    Persistent alteration in the quality and quantity of sleep has been implicated in sleep disorders leading to socio-economic consequences, due to chronic fatigue. Sleep deprived people may experience ‘microsleep’ states during which they are perceptually unaware of their surroundings and actions, and thereby potentially  endangering their lives and others. Sleep is also implicated in discrimination skills and procedural memory formation, with particular reference to slow wave sleep (NREM) sleep that occurs during early sleep [6,7]. Experience-dependent changes have been observed in the sleeping brain. For instance, when rats were exposed to rich sensorimotor experience in the preceding waking period, the immediate-early gene zif-268 is upregulated in the cerebral cortex of rats during sleep [8]. Most of behavioral regulation deficits caused by sleep operate through disruption of cognitive functions and self-control [9,10].

    Though there are more than 100 identified sleep/wake disorders, sleep complaints can be categorized broadly into five categories: hypersomnia, insomnia, circadian rhythm disorders, parasomnias, and sleep disorders associated with mental, neurological, and other medical disorders. Research that has been conducted over the last 50 years, and the advances made in clinical sleep medicine, have led to more effective treatments for the myriad human sleep disorders. However, an increasing area of concern is volitional or forced sleep deprivation due to work, stress, media and other reasons. Chronic sleep insufficiency is a health hazard relevant to present day life. Some causes can be attributed to work demands, education system, daily stress and medical disorders. Though acute sleep deprivation does not have or manifest any serious disorders, cumulative sleep debt can have serious effects on various body systems. In individuals with a prolonged sleep deficit, genetic changes were observed in the metabolic pathway that is involved in the regulation of cholesterol and inflammation [11] leading to decreased cholesterol transport and increased inflammation. Cholesterol has long known to be a predisposing factor to cardiovascular disease. In addition, it has been known to activate immune response [12] and modify glucose metabolism [13]. Epidemiological studies indicate that short or insufficient sleep is associated with increased risk for metabolic diseases and mortality.

    An equally disturbing trend is the chronic sleep insufficiency rampant among high school students. A youth risk behavior survey of high school students indicates that only 31% of high school students get the recommended amount of sleep while and students sleeping less than five hours were positively associated with all the 12 outcomes considered, some of which include texting while driving, physical fighting, suicidal ideation, binge drinking, sexual risk-taking, and obesity [14].

    Chronic sleep insufficiency is a public health crisis with serious consequences that we must address as a society. Both adults and teenagers are affected by this crisis, which can affect one’s well being in the workplace, at school or at home. Rather than treating sleep as an afterthought, we must strive to sleep the recommended 8 hours a day as frequently as possible, in order to keep our brains and bodies working in optimal condition.


References


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Sai Chandrasekhar

Sai Chandrasekhar


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