10 Stress and Sleep

Less stress, better sleep
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Better quality of sleep can be achieved by decreased amount of stress.
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The interplay between stress and sleep will be studied to understand how stress may lead to disturbances in sleep due to physiological changes. It is important to study this relationship because stress may induce negative effects on sleep, such that it produces physiological activation (i.e. increased cortisol levels), which can conflict with physiological deactivation in sleep. This may lead to stress induced sleeping disorders such as insomnia. For example, when a person is under a lot of pressure, such as that he is sleeping the night before a big exam, his sleep efficiency and the amount of time spend in deep sleep are both decreased due to stressfulness [1]. Moreover, the disturbance of sleep by stress may lead to other diseases such as cardiovascular diseases, obesity, diabetes, hormone regulation, and immune system regulation. On the contrary, the importance of sleep on alleviating the symptoms of stress is evident when the body attempts to moderate the stress-immune relationship. Researchers have found that sleep can be a mediator of the stress-immune relationship[2]. Thus, the more stressful people are, the lower the number of circulating natural killing cells, and the greater the time spent awake during non-REM sleep period. Moreover, a good amount of sleep may increase neurogenesis. Therefore, get a good night undisturbed sleep is the number one key step toward reducing stress.

Stress and Related Sleep Physiology

Sleep pattern

Normal human sleep consists of two alternating states: non-rapid eye movement (NREM) and REM sleep [1]. NREM can be divided into four stages in terms of EEG pattern (Fig.2). Stage 1 normally show low frequency EEG and high muscle tonus. This stage only persists for a few minutes and is easily to be disturbed. Stage 2 has increased EEG frequency (called sleep spindles) and occasional K-complexes. Muscle tonus has fallen further. This stage usually lasts for 10 to 25 minutes, and larger effort is needed to evoke arousal. Stage 3 and 4 are distinguished as Slow Wave Sleep (SWS), showing high frequency and very low muscle tonus[3]. On the contrary, REM sleep is defined by EEG activation, muscle atonia, and bursts of rapid eye movements. Several brain areas, such as hippocampus, amygdala, and occipital areas are largely awake during REM sleep. Dreaming is usually happening in REM sleep, yet because signals to muscle action are blocked, people will not act out dream during sleep. During sleep, physiological deactivation is occurred. Because adenosine triphosphate (ATP) normally provide energy to the brain during wake period, a breakdown of ATP is involved to induce sleep [1]. In the hypothalamus, there are neurons that are active during sleep while others are active during wake period. These neurons inhibit each other to maintain a stable wake-sleep cycle[4]. Stress disturbs this wake-sleep cycle by promoting physiological activation [1]. In one study, researchers have shown that various kinds of negative life events, such as death of spouse, can lead to large disturbance of sleep and even sleeping disorders. [5]

Figure 2
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EEG of 4 stages of NREM
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Negative Effects of Stress on Sleep

Stress Induced Sleeping Disorders - Insomnia

Figure 2
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EEG of 4 stages of NREM
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Insomnia is defined as having difficulties in sleeping for at least 3 months. Stress is considered the primary cause of insomnia [1]. Patients with insomnia also tend to have elevated cortisol levels and heart rate, which will be discussed in a later section; these changes indicate the increase in overall oxygen use in insomnia patients [6] [7][8]. One study showed that insomniacs reported the impact of daily minor stressors and intensive major negative life events are high on their everyday life, they thus perceived their life as more stressful [9]. These psychological stress events are observed to induce an increase in oxidizing substances in body, in which trigger oxidative stress by causing imbalance between oxidant production and antioxidant defences [8]. Sleep, on the other hand, will play an important role in enhancing antioxidant defense system. In another study by Abe and others, the characteristics of behaviors for coping with stress and sleep hygiene were examined on adults with Insomnia. Stressful life events such as divorce or pain may precipitate insomnia [10]. If people are inadequate in coping with stress, they may also experience the negative effects of insomnia, or unable to get a good night sleep. Thus, successfully coping with stress can relieve people from insomnia and/or comorbid depression.

Changes in Endocrine System

Various changes in endocrine system occur during sleep. Long-term stress response is mediated by hypothalamo-pituitary-adrenocortical (HPA) system. Hypothalamus activates sympathetic division of nervous system by releasing corticotropin-releasing hormone (CRH). CRH trigger the secretion of corticotropin (ACTH) from the anterior pituitary gland. Then cortisol is released from the adrenocortex, which may induce rise of blood volume and blood pressure. During the first stage of sleep, growth hormone (GH) is secreted and other hormones (ie. CRH, ACTH, and cortisol hormone) from the HPA system is suppressed [11]. This effect is exactly the opposite o f the effects of stress. resulting in increased SWS and decreased REM sleep [1]. GH will promote protein synthesis and prevents glucose from entering the cells; in this way, more circulating glucose is available in blood to serve as a constant supply to the brain during sleep [12]. On the other hand, if sleep is prevented, cortisol secretion will increase, creating similar effects as stress [13]. In a study by Steiger, he found out that administration of HPA hormones, CRH production increased, thus reducing SWS and increase in REM sleep during the first part of sleep [13]. Moreover, GH releasing hormone (GHRH) induces GH production and thus increased SWS, while CRH causes the opposite effect [11]. The quality of sleep depends on the balance between GHRH and CRH released. More CRH leads to shallower and more fragmented sleep. And changing in this balance may be also due to depression and aging [14]. Therefore, more stressful people are, more cortisol are released during sleep, causing significant decrease in quality of sleep.

Figure 1
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long term stress response
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Other possible diseases

Heart Diseases

Figure 4
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The Ideal Amount of Sleep in Adults at Risk for Diabetes and Heart Disease
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While cardiovascular disease is the leading cause of mortality and morbidity in western societies, it is important to understand and apply preventions; sleep, for example, is closely related to it. Back a century ago, people slept an average of 10 hours a night. In recent years, due to increase amount of stressful events, people only sleep on average of 7 hours per day [15]. sleep-deprivation is highly correlated with vascular diseases and high risk of http://en.wikipedia.org/wiki/Hypertension hypertension], as well as mortality (Fig.3). During NREM, heart rate, blood pressure, and cardiac output are all decreased because neural sympathetic activity is decreased. On the contrary, during REM sleep, increased sympathetic activity may cause increase in cardiovascular function [16]. In a prospective study illustrating the relationship between sleep duration and coronary heart disease in women, Najib and others have shown that short-term sleep derivation may increases cortisol levels, sympathetic neural activity, and blood pressure [17]. Long-term sleep-deprivation may impair endothelium-dependent vasodilation in the heart. Moreover, many patients suffering from insufficient sleep are obese or diabetic [18]. Changes in cortisol level due to sleep-deprivation may alter changes in GH production, which may induce diurnal rhythms and plasma levels of leptin. Appetite regulation will also be altered, thus causing obese or diabetes [19]. 

Positive Effects of Sleep on Stress

Stress-Immune Relationship

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People become less susceptible to infections and diseases if they have enough sleep [20]. SWS modulates immune system activity and disease processes [1]. In a study evaluating the relationship between sleep and immune system by comparing the amount of sleep get by day workers and shift workers showed that shift workers, who has more sleep loss and high levels of fatigue, tend to have more infections than day workers [21]. This is because the number of immune-cells, such as natural killing cells and other lymphocytes, decreased after sleep-deprivation. In addition, the number immune cells change according to how long the sleep-deprivation is (Table 1). Furthermore, sleep-deprivation induce the increase of inflammatory cytokines: Interleukin-1ß (IL-1ß), IL-6, and tumor necrosis factor-œ (TNF-œ) [22]. A study done by Vgontzas and others showed that these three cytokines are largely associated with patients who have excessive daytime sleepiness (EDS). Additionally, in a study conducted by Hall and others, they have found that sleep can be a mediator of the stress-immune relationship [2]. The more stressful people are, the lower the number of circulating natural killer cells, and the greater the time spent awake during NREM sleep period. Thus, sleeping well will get people become more immune and less stressful.

Sleep and Neurogenesis

Adult neurogenesis involves in learning and memory, anxiety regulation, and stress response [23]. Stress decreases proliferation of progenitor cells in the dentate gyrus of hippocampus [24]. This kind of inhibition of cell proliferation is been observed throughout life stages. Glucocorticoids have been indicated as regulating stress-related impairment of adult neurogenesis [23]. Removing circulating adrenal steroids may increase cell proliferation and thus neurogenesis. A similar approach to increase neurogenesis is to inhibit HPA axis activity, since HPA system releases cortisol [24]. Moreover, lack of sleep is stressful and will also reduce hippocampal neurogenesis. From one experiment, it is shown that after chronic sleep-deprivation of 2 weeks, neurogenesis is reduced and circulating glucocorticoids are elevated [25]. However, there is a temporary increase in formation of new neurons if normal sleeping pattern is restored. Therefore, having sufficient sleep is essential in both reducing stress as well as increase adult neurogenesis.

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