Circadian Rhythm Effects on Cardiovascular and Other Stress-Related Events.

Circadian rhythmicity is ensured by the circadian timing system based on input signals (environmental cues), an intrinsic rhythm generator and output rhythms. This system prepares organisms for changes in their physical environments, and to respond to environmental factors in a temporally appropriate matter. The hypothalamic-pituitary-adrenal (HPA) axis; the autonomic sympathetic nervous system; and the cardiovascular, metabolic, and immune systems contributing to maintain biological homeostasis during environmental or physiological challenges are characterized by the presence of a daily rhythm or by significant daytime variations. In combination to the individual differences in terms of diurnal preferences (chronotype), conditions evoking desynchronization of human circadian rhythms (shift-work, jet-lag exposure) or different stressors may induce significant changes in sympathetic-parasympathetic balance and tone of HPA axis. This condition in humans might negatively affect the cardiovascular system both chronically (by accelerating atherosclerosis) and acutely, via multiple mechanisms, triggering the onset of acute life-threatening events particularly in the morning. © 2017 Elsevier Inc. All rights reserved.