Why life oscillates--from a topographical towards a functional chronobiology.

Chronobiology has identified a multitude of rhythms within our body as well as within each living cell. Some of these rhythms, such as the circadian and circannual, interact with our environment, while others run on their own, but are often coupled to the circadian or to other body rhythms. Recent evidence shows that these rhythms might be more important for our health than expected: Disturbance of the circadian rhythms by jet lag or shift work not only evokes autonomic disturbances but also increases the incidence of cancer, as shown in this issue of Cancer Causes and Control. The occurrence of rhythms in the organism obviously bears several advantages: (1) It increases organismic stability by calibrating the system's characteristics: Regulation curves in time and space are crucial for controlling physiological long-term stability. To determine its properties continuously the system varies its parameters slightly over several time scales at different frequencies-akin to what our body does, e.g. in heart-rate variability. (2) Tuning and synchronization of rhythms saves energy: It was Huygens who observed that clocks on a wall tend to synchronize their beats. It turned out later that synchronisation is a very common phenomenon observed in bodies' rhythms and can be found, for example, when we relax or sleep. At such times energy consumption is minimal, our body working most efficiently. (3) Temporal compartmentalization allows polar events to occur in the same space unit: there are polarities in the universe of our body, which cannot happen simultaneously. Systole and diastole, inspiration and expiration, work and relaxation, wakefulness and sleep, reductive and oxidative states cannot be performed efficiently at the same time and place. Temporal compartmentalization is probably the most efficient way to mediate between these polarities. Chronobiology and chronomedicine are opening a new and very exciting understanding of our bodies' regulation. The biological time and its oscillations gain more attention and importance as these interrelations are understood.