Circadian rhythm and stress

Abstract

Rhythmicity of physiological parameters is found in virtually all living systems. The circadian rhythm with its most obvious expression, the sleep-wake cycle, is closely tied to the diurnal rhythm of day and night. A disturbance of this highly regulated system can lead to circadian misalignment resulting in sleeping difficulties with consequences on many physiological functions like psychological and physical performance, the metabolism, and the immune system as it could be found in night shift workers or in people suffering from chronic jet lag. Stress in its many forms, generally perceived as an excessive demand on human psychological and/or physiological adaptive capabilities, can have a direct influence on the human sleeping pattern due to the integration of neuronal and hormonal pathways of the stress reaction and the circadian regulation. Thus excessive and/or chronic stress can lead to a disturbance of the circadian rhythm as it can be found in diseases like depression and posttraumatic stress disorder. Extreme environments such as high altitude, hot or cold environments, or microgravity also can alter human sleep patterns as well as during isolation and confinement - experimental setups that serve to simulate the isolated nature of long-term space travel.