Light at night increases body mass and reduces glucose tolerance
Reseachers examined the effects of light at night (LAN) on body mass in male mice.
Mice exposed to a dim light at night gained 50 percent more weight over an eight-week period than mice that spent their nights in total darkness.
Mice housed in either bright or dim 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.
This significant increase in body mass was seen from Week 1 and continued throughout the study. By Week 4, both groups of mice showed impaired glucose tolerance. The mice exposed to LAN failed to recover glucose levels as effectively as the LD group. As little as 5 lx of light exposure during the typical dark period was sufficient to evoke this result.
Mice exposed to light at night had higher levels of glucose intolerance, which is a marker for pre-diabetes, than the mice that had complete darkness.
Light at night shifts eating schedules, causing weight gain
The researchers then did a second experiment with a timed feeding schedule. Both groups of mice had either continuous access to food or had food access limited to a light or dark phase.
Mice that lived in the dim-light conditions ate 55 percent of their food during daylight, compared with the mice in the standard light-dark conditions that ate 36 percent of their food in daylight.
With feeding in the light phase, mice increased their food consumption during week one; however, with feeding in the dark phase, mice consumed more food in subsequent weeks.
Even though mice are nocturnal creatures and would normally eat at night anyway, this difference shows their eating schedules were disrupted by artificial light. Low levels of light at night disrupt the timing of food intake and other metabolic signals, leading to excess weight gain.
“In many ways, our society now functions on a 24-hour-a-day schedule. These results suggest that such a schedule may impact metabolic function.” — Laura Fonken, PhD
References