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

TLDR

Obesity prevalence is rising alongside increased exposure to light at night and shift work, and circadian regulation of energy balance—synchronized by light—prepares the body for predictable events such as food intake and sleep, so disruption leads to 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. Male mice exposed to bright or dim light at night gained more body mass and had poorer glucose tolerance than those on a normal light/dark cycle, despite equal caloric intake and activity, because LAN shifted food consumption toward the light phase (55.5 % vs 36.5 % in controls) and restricting intake to the active phase prevented weight gain, indicating that low‑level nighttime light disrupts feeding timing and metabolic signals and may contribute to obesity.

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.