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To preserve your health, close the blinds when sleeping


Before going to bed, close the blinds, draw the curtains, and turn out all the lights. Even modest ambient brightness during nighttime sleep, as compared to sleeping in a poorly lit room, affects cardiovascular performance and raises insulin resistance the next morning, according to a new Northwestern Medicine research.

“The findings of this study show that even one night of moderate room lighting during sleep can impair glucose and cardiovascular regulation, which are risk factors for heart disease, diabetes, and metabolic syndrome,” said senior study author Dr. Phyllis Zee, chief of sleep medicine at Northwestern University Feinberg School of Medicine and a Northwestern Medicine physician. “It is critical for individuals to avoid or limit their exposure to light during sleeping.”


There is already evidence that daytime light exposure raises heart rate through sympathetic nervous system activation, which sends your heart into high gear and heightens awareness to tackle the difficulties of the day.


“Our findings suggest that a similar impact exists when light exposure occurs during nocturnal sleep,” Zee added.


The work will be published in PNAS on March 14th.


In a bright environment, the heart rate rises, and the body is unable to relax correctly.


“We found that sleeping in a fairly bright environment raises your heart rate,” said Dr. Daniela Grimaldi, a co-first author and research assistant professor of neurology at Northwestern. “Your autonomic nervous system is active even when you are sleeping. That’s not good. Your heart rate and other cardiovascular indicators are usually lower at night and greater throughout the day.”


Our physiology is regulated by sympathetic and parasympathetic nerve systems during the day and night. The sympathetic nervous system is in command during the day, while the parasympathetic nervous system is in charge at night, when it restores the whole body.

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How sleep deprivation caused by evening light may contribute to diabetes and obesity


Insulin resistance was discovered the morning after patients slept in a bright chamber, according to the researchers. Insulin resistance occurs when cells in your muscles, fat, and liver fail to react to insulin and are unable to utilise glucose from your blood for energy. To compensate, your pancreas produces extra insulin. Your blood sugar level rises with time.


An previous research published in JAMA Internal Medicine examined a large group of healthy persons who were exposed to light while sleeping. They were more overweight and obese, according to Zee.


“Now we’re demonstrating a process that might be crucial in explaining why this occurs,” Zee said. “We found that it had an effect on your capacity to manage glucose.”


The study’s participants were unaware of the biochemical changes that occurred in their bodies during night.


“But the brain detects it,” Grimaldi said. “It functions similarly to the brain of someone whose sleep is light and fragmented. The sleep physiology is not resting as it should.”


It is typical to be exposed to artificial light at night while sleeping.


Artificial light exposure during sleep is frequent, whether from interior light generating devices or from sources outside the house, especially in major cities. A significant number of people (up to 40%) sleep with a bedside lamp or a light on in the bedroom, and/or keep the television on.


Light has a two-edged connection with health.


“In addition to sleep, diet, and exercise, light exposure during the day is a significant determinant for health,” Zee said. “However, throughout the night, we demonstrate that even low-intensity light may affect measurements of heart and endocrine function.”

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The research compared sleeping with 100 lux (moderate light) versus sleeping with 3 lux (dim light) in subjects during a single night. The researchers observed that moderate light exposure led the body to become more awake. In this condition, the heart rate, the power with which the heart contracts, and the pace at which blood is delivered to your blood arteries for oxygenated blood flow all rise.


“These results are especially noteworthy for people living in contemporary civilizations where exposure to indoor and outdoor evening light is rising,” Zee added.


Zee’s top suggestions for avoiding light exposure while sleeping


(1) Do not switch on the lights. If you must have a light on (which older persons may need for safety), use a low light that is closer to the floor.


(2) Color is significant. A light that is amber or red/orange is less stimulating to the brain. Avoid using white or blue light, and keep it as far away from the sleeping individual as possible.


(3) If you can’t regulate the light outside, use blackout shades or eye masks. Adjust your bed so that the exterior light isn’t beaming in your eyes.


Is my room very bright?


“If you can see things well, it’s definitely too bright,” Zee added.


Other Northwestern authors include co-first author Ivy Mason, who was a post-doctoral fellow at Northwestern at the time of the study and is currently a research fellow at Harvard Medical School, Kathryn Reid, Chloe Warlick, Dr. Roneil Malkani, and Dr. Sabra Abbott.


The study was funded in part by the National Center for Advancing Translational Sciences award 8UL1TR000150-05, the National Heart, Lung, and Blood Institute grant R01 HL140580, the National Institute of Aging project P01AG11412, and the American Heart Association.

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