Since chronotherapy already manipulates rhythmical functions, it is the important task of chronohygiene to outline the object of therapy i.e. health, from chronobiological points of view. Only on such a basis can chronohygiene be extended to the preventive provisions of health care and health education in regard to the biological time structure. Health can be characterized as an optimal state of harmonious time structure and its integration into the temporal orders of the environment. The circannual variations of an organism establish a seasonal risk cycle changing the inner preconditions of therapy as well. Moreover, chronohygiene must raise the question of whether the biological circannual rhythm is an integrating component of the human time organization, or if it may be levelled by civilization. Circadian variations of the organism not only modify the preconditions of therapy, but in particular those of activity and efficiency. The nocturnal maximum of functional economy normally is protected against exploitation by a simultaneous minimum of vigilance, which provides the nightly recovery. Therefore the destruction of this phase relationship by night-work must worsen recovery conditions. The disturbance of the time structure in the organism by night-work not only affects the circadian system, but faster rhythms as well. The phase position of the circadian rhythms is closely related to the individual responsiveness of the autonomous system as well as to the pulse-respiration-ratio. The latter can serve as a chronobiological criterion for evaluating suitability or risk of night- and shift-work. The effort of chronohygiene is based on the fact that disturbances of the time structure represent just a complementary aspect to disturbances of the spatial structure of the organism.
