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Light exposure during sleep may harm your health, study says

Woman in pajama sleeping in bed at night. 

Story at a glance

  • Exposure to ambient light while sleeping at night can lead to an elevated heart rate and increased blood sugar the following day.
  • Chief of sleep medicine at Northwestern University Feinberg School of Medicine said the study’s results show one night of exposure to moderate light during sleep can “impair glucose and cardiovascular regulation.”
  • The study tested the effect of sleeping with moderate light and sleeping with dim light during a single night, with participants exposed to moderate light showing a heightened level of alertness.

A new study suggests exposure to ambient light while sleeping at night can lead to an elevated heart rate and increased blood sugar the following day.  

Senior study author Phyllis Zee, chief of sleep medicine at Northwestern University Feinberg School of Medicine, said in a news release the study’s results show one night of exposure to moderate light during sleep can “impair glucose and cardiovascular regulation.”  

The study, which was published Monday in PNAS, tested the effect of sleeping with moderate light and sleeping with dim light during a single night. Participants exposed to moderate light displayed a heightened level of alertness.  

Researchers noted the similarities between the way a person’s nervous system reacts to light both during the day — when light heightens awareness and increases the heart rate — and while asleep. 

“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,” Daniela Grimaldi, co-first author and research assistant professor of neurology at Northwestern, said. 

Meanwhile, researchers also found a link between sleeping in a lighted room and diabetes and obesity. They noted that people exposed to light while sleeping showed increased insulin resistance the morning after, which over time, can lead to elevated blood sugar levels. Zee said this added to findings from a previous study that found healthy people who were exposed to light during sleep were more overweight and obese. 

“Now we are showing a mechanism that might be fundamental to explain why this happens,” Zee said. “We show it’s affecting your ability to regulate glucose.”


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“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,” Zee added.    

Zee then offered advice for ways to mitigate the effects of nighttime light exposure. First, she said, keep the lights off. If this is not possible, avoid exposure to blue lights such as those from screens and keep them far from a sleeping person. If lights are necessary, choose a less stimulating color. Finally, Zee recommends black out curtains or eye coverings.  

There is one clear cut way to determining if one’s room is too bright, according to Zee.  

“If you’re able to see things really well, it’s probably too light,” Zee said. 


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Published on Mar 15,2022