Light, Circadian Rhythms and Health

Among the possible mechanisms utilized by living organisms to favor synchronization and adaptation to the environment, circadian (around 24 h) rhythms represent a crucial point. The day-night cycle, with light–dark alternation, is the strongest external circadian synchronizer for humans, capable to deeply influence also human individual differences (chronotype). However, since the 19th century, artificial light assumed an important role in regulating human life, including working activities (shift work). On one hand, satellite images have documented a worldwide increment of night-time illumination, and exposure to artificial Light-At-Night (LAN) is associated with a variegate spectrum of health problems. On the other hand, the growing use (and abuse) of technological devices (mostly emitting blue light, a powerful melatonin inhibitor), is transforming our society toward a progressive ‘eveningness’, with consequences on chronotype, sleep, lifestyle habits, and health.