Chronobiology and Obesity: The Orchestra Out of Tune

Marta Garaulet; Purificación Gómez-Abellán; Juan Antonio Madrid

Disclosures

Clin Lipidology. 2010;5(2):181-188. 

In This Article

Background: What is Chronobiology?

The concept of time is difficult to define from a physical point of view and even today there is no clear definition on what time is. It has been defined as "the continuous passage of existence in which events pass from a state of potentiality in the future, through the present, to a state of finality in the past".[1] Time is also, "a moment, hour, day or year as indicated by a clock or a calendar".[1]

Since ancient times, the human being has had a need to measure and predict the time by means of developing clocks and calendars. However, a revolution in timekeeping came about with the invention of mechanical clockworks in the 1200s. The beginning of these modern clocks came from the requirements of religious persons, who were required to perform their duties regularly, knowing the times for their appointed prayers.[1]

Nevertheless, millions of years before humans developed the first calendar or invented the first artificial clock, living organisms started to develop mechanisms to measure time at a wide variety of scales: daily, tidal, lunar and annual. Living organisms present a huge number of processes that occur in a periodic and predictable manner that can be termed biological rhythms. The first specific report of a biological rhythm was provided by the French astronomer Jean Jacques d'Ortous De Marian in 1729,[2] who reported the follicular movements of the plant Mimosa pudica. De Marian demonstrated that the opening and closing leaf movements remained under constant darkness conditions for several days.

It was in the middle of the 20th Century when a new field of science, known as chronobiology emerged. Some of the first studies were performed by insect ecologist Colin S Pittendrigh in the fruitfly Drosophila, who discovered the basic principles on which the actual chronobiology was based.[3] Chronobiology is a word derived from three Greek stems: kronos for time, bios for life and logos for study. It is a scientific field which studies the timing processes (the biological rhythms) that occur in the living organisms at their different levels of organization. Circadian rhythms are genetically determined rhythms with near 24-h periodicity, that persist in constant darkness, such as the rhythms of secretion of some hormones (e.g., cortisol and melatonin). Ultradian rhythms refer to those rhythms that have a frequency of higher than one cycle per day (period less than 20 h, e.g., breathing, heart beats and intestinal movements) while infradian rhythms are those whose frequency is lower than one cycle per day (period of >28 h) such as the circalunar rhythms or the menstrual cycle in humans.[1] All of these types or rhythms characterize biological function in different animal species, including humans.

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