![]() In addition, research on the association between sleep and HPA activity among patients with insomnia has revealed inconsistent results. A recent study reports that sleep deprivation associates with higher morning cortisol levels, whereas sleep misalignment leads to lower morning cortisol levels ( Wright et al., 2015). Further research by well-control equipment for objective analysis of sleep architectures would be helpful for explaining these discrepancies in results.īroad controversies over the association of sleep with HPA activity indicate that this association is not a static unidirectional relation but a dynamic one modulated by different aspects of sleep characteristics. These different results that ranged from positive or negative association to no relation between sleep and HPA activity call for more investigation in this area. Moreover, some studies did not indicate any association between sleep and HPA axis activity at all ( Lattova et al., 2011 Varkevisser, Van Dongen, & Kerkhof, 2005). (2004) reported a relation between awakening time and cortisol level but no association between sleep duration and cortisol. Some studies failed to find any association between sleep duration and cortisol level. In contrast, increased serum cortisol level has been reported among people with insomnia in many previous studies, too ( Floam et al., 2015 Meerlo et al., 2007 Rodenbeck & Hajak, 2001 Rodenbeck, Huether, Rüther, & Hajak, 2002). ![]() Similarly, reduced cortisol level after 24 h sleep deprivation has been reported ( Arnal et al., 2016). Based on a study conducted on 58 normal adults on the association among sleep, stress and cortisol awakening response, lower subjective total sleep time is significantly related to lower cortisol levels at awakening ( Vargas & Lopez-Duran, 2014). Association between sleep duration and awakening cortisol level has been already reported. Despite the high prevalence of insomnia and its adverse health and economic outcomes, the biological mechanisms of bidirectional interaction between stress systems and sleep have not been fully understood.Īlthough there is a physiological link between neural representation of sleep-wake cycle and stress-responsive systems, inconsistent results have been reported about association between sleep architectures and cortisol level, the final product of HPA ( Elder, Wetherell, Barclay, & Ellis, 2014). To call it insomnia, it should occur at least three times per week, and produce clinically significant impairment in social, occupational or other aspects of subject’s functions ( American Psychiatric Association, 2013). ![]() It is defined as difficulties in initiating and maintaining sleep, or early-morning awakening with inability to return to sleep. Insomnia is the most prevalent sleep disorder that affects 10% of adult population ( Morin & Benca, 2012 Ohayon & Reynolds, 2009). Therefore, sleep duration may change the patterns of stress systems ( Edwards, Evans, Hucklebridge, & Clow, 2001). In addition, brain centers that control sleep-wake cycle and stress-responsive biological systems are closely interrelated. Sleep disturbances change the autonomic activity and increase heart rate and blood pressure (Zhong et al., 2005). Previous studies have emphasized that the circadian mechanisms which control the sleep, also directly modulate ANS ( Leproult & Van Cauter, 2010). ![]() SCN as a circadian pacemaker is also responsible for modulation of sleep-wake cycle (Hastings, Reddy, & Maywood, 2003). ![]() Hypothalamus-Pituitary-Adrenal (HPA) and Autonomic Nervous System (ANS) are controlled by Suprachiasmatic Nucleus (SCN) of hypothalamus. Biological rhythms that regulate two main stress systems, i.e. In particular, sleep duration and quality could alter biological systems responses to stress ( Meerlo, Sgoifo, & Suchecki, 2007). Poor sleep quality could also disrupt the endocrine system ( Ioja, Weir, & Rennert, 2012 Mullington, Simpson, Meier-Ewert, & Haack, 2010 Potter et al., 2016). Sleep is an important body homeostatic behavior that plays a critical role in emotional and cognitive functions ( Koren et al., 2011). ![]()
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