Light at night increases body mass by shifting the time of food intake

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.circadian rhythms | light pollution | metabolic syndrome | mice | obesity D uring the past 2 decades, obesity has shifted from an epidemic centered in the United States to a global issue. Although well-documented factors such as caloric intake, dietary choices, and lack of exercise are known to contribute to the prevalence of obesity and metabolic disorders, additional environmental factors are now considered critical in the development and maintenance of obesity (1). The increase of light at night (LAN) during the 20th century coincides with increasing rates of obesity and metabolic disorders throughout the world. Artificial lighting allows people to extend daytime activities into the night but as a consequence produces significant environmental light pollution caused by light straying into the atmosphere and brightening the nighttime sky.Circadian regulation of energy homeostasis is controlled by an endogenous biological clock, located in the suprachiasmatic nuclei (SCN) of the hypothalamus, that is synchronized by photic information that travels directly from light-sensitive ganglion cells in the retina to the SCN, thereby entraining individuals' physiology and behavior to the external day-night cycle (2). Importantly, light is the most potent entraining signal for the circadian clock, although other factors such as food consumption influence clock signaling (3). To promote optimal adaptive functioning, the circadian clock prepares individuals for predictable events such as food availability and sleep. Shift work disrupts ...

Chronobiology by moonlight

“…Light at night was shown to have negative effects in rodents when chronically administered at intensities comparable with those of street lamps (approx. 5-20 lux): it can suppress immune-function in hamsters [137] and cause obesity in male mice [138]. Even exposure to dim light at night may negatively affect the circadian system of mammals, especially rodents, as evident by changes in clock genes expression patterns [139].…”

Melatonin: a possible link between the presence of artificial light at night and reductions in biological fitness

“…Convincing support for the link between LAN and significant modifications to both behaviour (activity patterns) and physiology (moult dates and reproductive status) also comes from a series of long-term studies combining field and experimental trials on European blackbirds (Turdus merula) [12,18,28,29]. However, despite the recent surge in research on the impacts of night lighting within the fields of ecology and medicine, we still lack broad-scale, cross-species experimental evidence of the negative effects of LAN (but see [30]). Data on wild populations that experimentally link LAN to decreased biological function are notably absent and the underlying mechanisms driving the observed changes remain both poorly understood and largely vertebrate focused.…”

Impact of circadian misalignment on energy metabolism during simulated nightshift work

“…Evidence from nonhuman animal models reveals that consumption of calories at inappropriate circadian times contributes to weight gain (15,16). Further, caloric intake during typical sleep time leads to greater weight gain than the same caloric intake during typical waketime (15,16).…”