Healio: Among healthy adults, one night of moderate light during sleep compared with sleep in a dimly lit environment increased nighttime heart rate and next-morning insulin resistance, concluded new research.

“Interestingly, the effect of nighttime light exposure on metabolic function was correlated with an increase in sympathovagal balance during sleep,” Phyllis C. Zee, MD, PhD, a neurologist and professor and chief of sleep medicine in neurology at the Northwestern University Feinberg School of Medicine, and colleagues wrote.

According to the researchers, ambient nighttime light exposure during sleep is implicated as a risk factor for adverse health outcomes, including cardiometabolic disease. “However, the effects of light during sleep on cardiometabolic outcomes and the related mechanisms are unclear,” they wrote.

In the study, Mason and colleagues aimed to determine whether nighttime light negatively affects next-morning glucose homeostasis and whether this effect occurs through reduced sleep quality, melatonin suppression or sympathetic nervous system activation during sleep.

The study featured a parallel-group design. Researchers enrolled 20 young adults whom they divided into two arms: the room light condition arm (n = 10), in which participants received one night of sleep in dim light (<3 lux) followed by one night of sleep with overhead room lighting (100 lux); and the dim light condition arm (n = 10), in which participants experienced two consecutive nights of sleep in dim light.

“These results demonstrate that a single night of exposure to room light during sleep can impair glucose homeostasis, potentially via increased sympathetic nervous system activation. Attention to avoiding exposure to light at night during sleep may be beneficial for cardiometabolic health.”

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