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Fonken, L. K., Weil, Z. M., & Nelson, R. J. (2013). Dark nights reverse metabolic disruption caused by dim light at night. Obesity (Silver Spring), 21(6), 1159–1164.
Abstract: OBJECTIVE: The increasing prevalence of obesity and related metabolic disorders coincides with increasing exposure to light at night. Previous studies report that mice exposed to dim light at night (dLAN) develop symptoms of metabolic syndrome. This study investigated whether mice returned to dark nights after dLAN exposure recover metabolic function. DESIGN AND METHODS: Male Swiss-Webster mice were assigned to either: standard light-dark (LD) conditions for 8 weeks (LD/LD), dLAN for 8 weeks (dLAN/dLAN), LD for 4 weeks followed by 4 weeks of dLAN (LD/dLAN), and dLAN for 4 weeks followed by 4 weeks of LD (dLAN/LD). RESULTS: After 4 weeks in their respective lighting conditions both groups initially placed in dLAN increased body mass gain compared to LD mice. Half of the dLAN mice (dLAN/LD) were then transferred to LD and vice versa (LD/dLAN). Following the transfer dLAN/dLAN and LD/dLAN mice gained more weight than LD/LD and dLAN/LD mice. At the conclusion of the study dLAN/LD mice did not differ from LD/LD mice with respect to weight gain and had lower fat pad mass compared to dLAN/dLAN mice. Compared to all other groups dLAN/dLAN mice decreased glucose tolerance as indicated by an intraperitoneal glucose tolerance test at week 7, indicating that dLAN/LD mice recovered glucose metabolism. dLAN/dLAN mice also increased MAC1 mRNA expression in peripheral fat as compared to both LD/LD and dLAN/LD mice, suggesting peripheral inflammation is induced by dLAN, but not sustained after return to LD. CONCLUSION: These results suggest that re-exposure to dark nights ameliorates metabolic disruption caused by dLAN exposure.
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Fonken, L. K., Workman, J. L., Walton, J. C., Weil, Z. M., Morris, J. S., Haim, A., et al. (2010). Light at night increases body mass by shifting the time of food intake. Proc Natl Acad Sci U S A, 107(43), 18664–18669.
Abstract: The global increase in the prevalence of obesity and metabolic disorders coincides with the increase of exposure to light at night (LAN) and shift work. Circadian regulation of energy homeostasis is controlled by an endogenous biological clock that is synchronized by light information. To promote optimal adaptive functioning, the circadian clock prepares individuals for predictable events such as food availability and sleep, and disruption of clock function causes circadian and metabolic disturbances. To determine whether a causal relationship exists between nighttime light exposure and obesity, we examined the effects of LAN on body mass in male mice. Mice housed in either bright (LL) or dim (DM) LAN have significantly increased body mass and reduced glucose tolerance compared with mice in a standard (LD) light/dark cycle, despite equivalent levels of caloric intake and total daily activity output. Furthermore, the timing of food consumption by DM and LL mice differs from that in LD mice. Nocturnal rodents typically eat substantially more food at night; however, DM mice consume 55.5% of their food during the light phase, as compared with 36.5% in LD mice. Restricting food consumption to the active phase in DM mice prevents body mass gain. These results suggest that low levels of light at night disrupt the timing of food intake and other metabolic signals, leading to excess weight gain. These data are relevant to the coincidence between increasing use of light at night and obesity in humans.
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Haim, A., Shanas, U., Zubidad, A. E. S., & Scantelbury, M. (2005). Seasonality and Seasons Out of Time--The Thermoregulatory Effects of Light Interference. Chronobiol Int, 22(1), 59–66.
Abstract: The change in photoperiod is the main environmental cue for seasonal function of the reproductive, thermoregulatory, and immune systems in rodents existing outside of the tropics. In Israel, the social vole Microtus socialis breeds mainly under short photoperiod (SP) conditions. Previous studies showed that exposing voles to light interference (LI) in the field during the winter resulted in death. The aim of the current study was to determine the thermoregulatory response of SP-acclimated voles to LI. Therefore, heat production (VO2) at different ambient temperatures (Ta) and nonshivering thermogenesis (NST) were measured. Results show that LI of 15 min every 4h during the dark period significantly (p < 0.02) decreased VO2 at Ta = 15 degrees C and significantly (p < 0.05) decreased NST-capacity. These results can at least partly explain why LI-voles died during the winter under field conditions, through eliminating winter acclimatization of the thermoregulatory system, or what is considered as “seasons out of time.”
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Kantermann, T. (2013). Circadian biology: sleep-styles shaped by light-styles. Curr Biol, 23(16), R689–90.
Abstract: Light and darkness are the main time cues synchronising all biological clocks to the external environment. This little understood evolutionary phenomenon is called circadian entrainment. A new study illuminates our understanding of how modern light- and lifestyles compromise circadian entrainment and impact our biological clocks.
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Longcore, T. (2010). Sensory ecology: night lights alter reproductive behavior of blue tits. Curr Biol, 20(20), R893–5.
Abstract: Research on songbirds indicates that streetlights influence timing of dawn chorus, egg-laying and male success in siring extra-pair young, providing new evidence that artificial lighting is an ecologically disruptive force.
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