In a recently published study from the Proceedings of the National Academy of Sciences, the authors concluded that avoiding exposure to light at night during sleep maybe beneficial for cardiometabolic health.
Senior study author Phyllis Zee, chief of sleep medicine at Northwestern University Feinberg School of Medicine, and colleagues explored the potential impact of acute light exposure during what otherwise would be planned sleep time spent in darkness. The investigators set out to explore whether this unnatural exposure to light reduced sleep quality, melatonin secretion, and other potential influences on the sympathetic nervous system.
According to Dr. Zee, who is also a Northwestern Medicine physician, "The results from this study demonstrate that just a single night of exposure to moderate room lighting during sleep can impair glucose and cardiovascular regulation, which are risk factors for heart disease, diabetes and metabolic syndrome." Dr. Zee further elaborated, "It's important for people to avoid or minimize the amount of light exposure during sleep. Our results indicate that a similar effect is also present when exposure to light occurs during nighttime sleep."
The investigators included 20 young adults in their parallel-group study design where they explored the impact of one night of sleep with dim light followed by one night of sleep with overhead room lighting on measures of insulin resistance using a morning homeostatic model assessment of insulin resistance and a 30-minute insulin area under the curve (AUC) from a 2-hour oral glucose tolerance test, which were higher in the light versus dim light condition. Melatonin levels, however, were similar in both lighted conditions.
The team reported that they observed higher heart rates and lower heart rate variability during sleep in the light room versus the dim light condition, which translated into higher sympathovagal balance. The researchers noted that this was associated with higher 30-minute insulin AUC, consistent with increased insulin resistance the following morning.
In support of these findings, Daniela Grimaldi, co-author and research assistant professor of neurology at Northwestern, stated, "We showed your heart rate increases when you sleep in a moderately lit room." Dr. Grimaldi added, "Even though you are asleep, your autonomic nervous system is activated. That's bad. Usually, your heart rate together with other cardiovascular parameters are lower at night and higher during the day."
"Now we are showing a mechanism that might be fundamental to explain why this happens," Dr. Zee stated. "We show it's affecting your ability to regulate glucose. In addition to sleep, nutrition and exercise, light exposure during the daytime is an important factor for health, but during the night we show that even modest intensity of light can impair measures of heart and endocrine health."
Dr. Zee concluded, "These findings are important particularly for those living in modern societies where exposure to indoor and outdoor nighttime light is increasingly widespread."
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