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Unformatted text preview: MINI REVIEW The dark side of light at night: physiological, epidemiological, and ecological consequences Introduction Successful organisms must adapt to temporal, as well as spatial niches. Endogenous biological clocks allow individ- uals to anticipate and adapt to the daily light-dark cycles in their environments to optimally time metabolism, physiol- ogy, and behavior each day. Rodents in nontropical environments, for example, alter reproductive, metabolic , and immunological activities  based on changes in day length throughout the seasons. The timing of avian reproduction and molt also often depends upon seasonal changes in day length , and many species, including some birds [4,5], rodents , bats , and marine animals , adjust foraging activities according to changes in the lunar cycle. Aside from seasonal adjustments, there is marked circadian variation in physiological functions. In many species, including some birds, rodents, fish, and humans, for example, circulating concentrations of sex steroids [9–11] and glucocorticoids  vary with the light/dark cycle throughout the day, causing corresponding changes in reproductive activities  and metabolic functions . Responses to natural light cycles result in an adaptive temporal organization in humans and other animals. With the invention and use of electrical lights, beginning about a century ago, this temporal organization has been dramat- ically altered. Light at night has significant social, ecolog- ical, behavioral, and health consequences that are only now becoming apparent. The extensive control that light-driven mediators exert upon multiple body systems, for example, creates numerous targets on which light-induced disrup- tions can act, resulting in a wide range of physiological changes and potentially serious medical implications. In a broader context, underpinning physiological mechanisms regulate a variety of behaviors, ranging from reproduction to foraging, creating expansive targets for light disruption. Assuming that adaptive processes have optimized the physiological and behavioral regulation of animals accord- ing to changing day lengths and circadian cycles, artificial changes in light cycles could have drastic fitness effects. This review summarizes the medical and ecological implications of exposure to artificial light at night, and related distur- bances in normal seasonal and circadian physiological and behavioral functions. Sources of light at night Light pollution by urban development Urban development has brought the need for artificial lighting of roadways, shopping centers, stadiums, and homes. Some of this light strays and scatters in the atmosphere, bringing about a brightening of the natural sky beyond background levels, called urban sky glow [15,16]. Light pollution has demonstrated effects on daily 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50...
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- Winter '08
- Sula, Circadian rhythm, melatonin levels, Light pollution, Constant Light