L'évolution du rythme veille-sommeil au cours de l'histoire de l'humanité. Influence de la lumière artificielle

Artificial lighting which appeared late in the history of humanity has changed sleep qualitatively and quantitatively. Literature from Homer to Dickens reported that the nocturnal biphasic sleep was initially dominant, favored by natural light dark cycle. It consisted of two phases broken by a 1 to 3 hours nocturnal awakening. With the development of the domestic light, it was gradually abandoned. The sleep time has got shorter due to the constraints imposed by the societal time. The circadian clock which regulates the sleep-wake cycle has shifted to the morning. This phenomenon has speeded up in recent years, with practice of activities involving screens and mobilizing attention. A true “social jet lag” set in, with consequences on the physical and mental health. Urban lighting has emerged from the 16th century, for reasons of safety and comfort, and today to satisfy other concerns, particularly artistic. Professional and amateur astronomers (ANPCEN) denounced a move which led to a real light pollution. Governments have recognized the harm caused to human health and the living world (Act 2009 s.41 Grenelle I). A flashback is initiated with the removal of lights in unoccupied buildings and shops at night (decree in January 2013). Some common public streetlights are off from midnight, with consequences on the quality of life that would be interesting to evaluate. Overall exposure of organisms to alternating light dark whose amplitude is dampened leads to an alteration of human health that extends beyond sleep disorders (such as the increased incidence of cancer among shift workers).