Circadian rhythms in glucose and lipid metabolism in nocturnal and diurnal mammals

Most aspects of energy metabolism display clear variations during day and night.

• The daily rhythmicity of metabolic functions is regulated by a circadian system involving the master clock in the hypothalamus and secondary clocks in other organs.
• The suprachiasmatic nuclei (SCN) influence peripheral timing through the autonomic and neuroendocrine systems.
• In diurnal and nocturnal species, hormonal rhythms often show opposite phases relative to the light-dark cycle, despite the SCN clock being active at the same astronomical times.
• Pineal melatonin is secreted only at night in both diurnal and nocturnal mammals.
• Circadian clock impairments and misalignments, such as those caused by shift work or chronic jet-lag, may adversely affect energy metabolism and could contribute to obesity and diabetes.

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