Light exposure during sleep yields impairment in cardiometabolic function
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Among healthy adults, one night of moderate light exposure 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 is implicated as a risk factor for adverse health outcomes, including cardiometabolic disease. “However, the effects of nighttime light exposure during sleep on cardiometabolic outcomes and the related mechanisms are unclear,” they wrote.
In the study, Mason and colleagues aimed to determine whether acute exposure to light during nighttime sleep 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.
The two groups were similar in age, BMI, sex and race, and had a similar bedtime, sleep duration and sleep efficiency in the week preceding the laboratory stay.
Researchers determined insulin resistance via morning homeostatic model assessment of insulin resistance and 30-minute insulin area under the curve from a 2-hour oral glucose tolerance test.
Compared with the dim light condition arm, those in the room light arm had greater insulin resistance, whereas the groups had comparable levels of melatonin.
Researchers reported that participants in the light condition group spent proportionately more time in stage N2 and less time in slow wave and rapid eye movement sleep, and had a higher heart rate and lower heart rate variability (higher sympathovagal balance) during sleep.
“Importantly, the higher sympathovagal balance during sleep was associated with higher 30-minute insulin AUC, consistent with increased insulin resistance the following morning,” the researchers wrote.
“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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