Sleep, circadian rhythms, and environmental light pollution: Public health issues

All life forms evolved under and adapted to annual, lunar and 24-hour (h) natural environment photoperiodicities. The biology of the diurnal human species is geared for activity during the light of day and sleep during the dark of night. Since the invention of the incandescent light bulb, modern technologies have created an unnatural environment in which moderate to bright light exposure may be present throughout the entire 24h. Artificial light enables extension of the normal diurnal span of human activity and productivity, but it also can alters biology, especially the 24h sleep-wake cycle. The consequence is reduced nighttime sleep of adults and children. The 2005 National Sleep Foundation survey found ~25% of Americans sleep <7 h/weekday. Such sleep loss can result in significant decrease in prolactin, melatonin, growth and (ghrelin which stimulates and leptin which inhibits) appetite hormones. Artificial light and modern technologies have enabled the growth of night and rotating shift-work schedules, currently involving 15-20% of the US workforce. These work schedules severely compromise sleep duration and quality. Night work is a risk factor for industrial accidents and injuries and several medical conditions, including cancer especially in women. Overall, sleep loss and nighttime light exposure pose serious, but as yet unappreciated, public health problems.