Stress hormones and sleep disturbances - electrophysiological and hormonal aspects.

In noise effect research often the awakening reaction is maintained to be the only important health related reaction. The main argument is that sleep represents a trophotropic phase ("energy storing"). In contrast to this awakening reactions or lying awake belong to the ergotropic phase ("energy consuming"). Frequent or long awakening reactions endanger therefore the necessary recovery in sleep and, in the long-run, health. Findings derived from arousal and stress hormone research make possible a new access to the noise induced nightly health risk. An arousal is a short change in sleeping condition, raising the organism from a lower level of excitation to a higher one. Arousals have the function to prevent life-threatening influences or events through activation of compensation mechanisms. Frequent occurrences of arousal triggered by nocturnal noise leads to a deformation of the circadian rhythm. Additionally, the deep sleep phases in the first part of the night are normally associated with a minimum of cortisol and a maximum of growth hormone concentrations. These circadian rhythms of sleep and neuroendocrine regulation are necessary for the physical as well as for the psychic recovery of the sleeper. Noise exposure during sleep which causes frequent arousal leads to decreased performance capacity, drowsiness and tiredness during the day. Long-term disturbances of the described circadian rhythms have a deteriorating effect on health, even when noise induced awakenings are avoided.