For the study—published in the journal, Sleep—researchers recruited 20 healthy adult volunteers (ages 18 to 40). The volunteers spent two nights and three days at the lab: The first night, they slept in pitch black darkness; the second night, half of them slept in the dark again while the other half slept in a room with a bright overhead light on. While the volunteers slept, the researchers tracked the volunteers’ vital signs, brain wave activity, and leg and eye movements; they also took hourly blood samples to measure melatonin—a vital hormone that helps control your internal clock (circadian rhythm) and typically rises during sleep. In the morning, the researchers conducted glucose tolerance tests on the volunteers.
Remarkably, just sleeping under a bright light drove up insulin resistance—a risk factor for diabetes. When insulin can’t do its job, the body struggles to process sugar. “Our preliminary findings show that a single night of light exposure during sleep acutely impacts measures of insulin resistance,” said lead author Ivy Cheung Mason, PhD, a postdoctoral fellow at Northwestern’s Feinberg School of Medicine (at the time of the study), in a press release.