Restricted and disrupted sleep: effects on autonomic function, neuroendocrine stress systems and stress responsivity.

Frequently disrupted and restricted sleep is a common problem for many people in our modern around-the-clock society. In this context, it is an important question how sleep loss affects the stress systems in our bodies since these systems enable us to deal with everyday challenges. Altered activity and reactivity of these systems following insufficient sleep might have serious repercussions for health and well-being. Studies on both humans and rodents have shown that sleep deprivation and sleep restriction are conditions often associated with mild, temporary increases in the activity of the major neuroendocrine stress systems, i.e., the autonomic sympatho-adrenal system and the hypothalamic-pituitary-adrenal axis. Sleep deprivation may not only have a direct activating effect by itself but, in the long run, it may also affect the reactivity of these systems to other stressors and challenges. Although the first signs of alterations in the way people deal with challenges under conditions of restricted sleep appear to be on the level of emotional perception, chronic sleep restriction may ultimately change the fundamental properties of neuroendocrine stress systems as well. Understandably, few controlled studies in humans have been devoted to this topic. Yet, experimental studies in rodents show that chronic sleep restriction may gradually alter neuroendocrine stress responses as well as the central mechanisms involved in the regulation of these responses. Importantly, the available data from studies in laboratory animals suggest that sleep restriction may gradually change certain brain systems and neuroendocrine systems in a manner that is similar to what is seen in stress-related disorders such as depression (e.g., reduced serotonin receptor sensitivity and altered regulation of the hypothalamic-pituitary-adrenal axis). Such data support the view that insufficient sleep, by acting on stress systems, may sensitize individuals to stress-related disorders. Indeed, epidemiological studies suggest that sleep complaints and sleep restriction may be important risk factors for a variety of diseases that are often linked to stress, including cardiovascular diseases and mood disorders.