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

Circadian Rhythms in Humans

Nowadays, a considerable number of circadian rhythms have been documented in humans. The timing of sleep and wakefulness, feeding and drinking behaviors; thermoregulation; and endocrine, renal and reproductive function all display circadian rhythmicity.

However, the endogenous nature of circadian rhythms in humans appears to have been ignored until William Ogle in 1866 carried out careful observations of the daily body temperature rhythm in humans.[4] In his own words: "there is a rise in the early mornings while we are still asleep and a fall in the evening while we are still awake". Later it was conclusively demonstrated that the rhythm of human body temperature was endogenous. Nowadays, body temperature is one of the physiological variables more generally used in chronobiological studies performed in humans.

Circadian rhythms have now been documented in a wide variety of hormones. The expression rhythms of cortisol, growth hormone, aldosterone, prolactin, testosterone, thyrotropin, luteinizing hormone (LH) and follicle-stimulating hormone are some examples.[5] Adipose tissue, currently considered as an endocrine organ, has the circadian clock machinery required to be defined as a peripheral circadian oscillator.[6] In this sense, hormones and cytokines highly related to adipose tissue display circadian rhythmicity. Some examples are leptin, adipsin, resistin, adiponectin and visfatin.[7] Adiponectin has been proposed as a 'guardian angel' against metabolic syndrome disturbances. Its circulating levels exhibit both ultradian pulsatility and a diurnal variation.[8] In this regard, the knowledge of the circadian rhythmicity of these substances is a key element for the understanding of the human physiology and pathophysiology, and in particular for the understanding of obesity.

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