Just one night spent sleeping in a moderately lit room can lead to a higher heart rate during the night and insulin resistance the next morning. A new study included two groups of ten healthy adults. One group slept in dimly lit rooms for two consecutive nights and the other slept in dimly lit rooms one night and then moderately lit rooms the next. The moderately lit rooms were illuminated with a 100 lux overhead light, which is about as bright as it would be on an overcast day. A 100 lux light could also be compared to a lit television screen in a darkened room or a standard street light shining through a thinly veiled window.
All the study participants wore heart monitors to sleep. On the second night, the group that slept in moderately lit rooms showed a marked increase in heart rate while they slept compared to the night before. The group that slept in dim lighting both nights showed no significant change. “We showed your heart rate increases when you sleep in a moderately lit room,” said Daniela Grimaldi, assistant professor of neurology at Northwestern University. “Even though you’re asleep, your autonomic nervous system is activated.” The autonomic nervous system regulates involuntary bodily processes such as breathing, heart rate, pupil dilation and digestion, as well as the fight-or-flight response.