[Internal clock desynchronization and public health consequences]

Internal clock desynchronization and public health consequences. The internal clock which is located in the suprachiasmatic nuclei of the hypothalamus is controled by genetic factors (clock genes) and environmental factors (light-dark and sleepwake alternations). Light is the major component of the clock control. Clock desynchronization occurs when the clock is no longer in phase with the environment resulting in a phase shift (phase advance or phase delay) which can produce fatigue, sleep and mood disorders. Chronic exposure to light at night results in a clock desynchronization with concomitant health issues. This paper reports on the effects of the chronic desynchronization experienced by shiftworkers and nightworkers (which is a public health issue) and also by a large number of children and adolescents who sleep for 7-8 h instead of 9-10 h per night in relation with their use at night of electronic media. This sleep debt can lead to fatigue, behavioral problems and poor academic achievement.