Any light exposure during sleep can lead to obesity, diabetes, high blood pressure

CHICAGO — Does a bright smartphone screen often wake you up in the middle of the night? A new study finds any kind of light exposure during sleep can significantly increase the risk of developing obesity, diabetes, or high blood pressure — especially in older adults.

While examining over 500 older men and women between 63 and 84, researchers from Northwestern University found that harmful light exposure can come from all sorts of places, including room lights left on for safety, bedrooms without blackout shades, and digital devices lighting up at odd hours.

The team tracked these individuals for seven days, measuring their exposure to light using wrist-worn devices under real-world conditions. They found that older adults who did not get a five-hour period of complete darkness each day were much more prone to develop these conditions than those getting uninterrupted sleep.

“Whether it be from one’s smartphone, leaving a TV on overnight or light pollution in a big city, we live among an abundant number amount of artificial sources of light that are available 24 hours of a day,” says study corresponding author Dr. Minjee Kim, an assistant professor of neurology at Northwestern University Feinberg School of Medicine and a Northwestern Medicine physician, in a media release. “Older adults already are at higher risk for diabetes and cardiovascular disease, so we wanted to see if there was a difference in frequencies of these diseases related to light exposure at night.”

Most older adults are not getting a light-free sleep

Using the light trackers, researchers discovered that fewer than half of the 552 participants in their study consistently enjoyed a five-hour period in total darkness each night. Moreover, this light was shining on them during the darkest periods of the night and during the middle of someone’s typical sleep cycle.

Study authors caution, however, that their findings don’t reveal which condition is causing the other. Are obesity, diabetes, and hypertension causing people to sleep with more lights on, or are lights causing these changes in the human body?

The team also says that individuals with these health problems may be more likely to get up and go to the bathroom in the middle of the night — turning on more lights. Others with foot numbness, due to diabetes, may also keep more lights on at night to reduce the risk of falling.

“It’s important for people to avoid or minimize the amount of light exposure during sleep,” says senior study co-author Dr. Phyllis Zee, chief of sleep medicine at Feinberg and a Northwestern Medicine physician.

For now, Dr. Zee has a few key recommendations for older adults:

  • Don’t turn lights on. If you must have a light on, use a dim light closer to the floor.
  • Color is important. Use amber or red/orange lights which are less stimulating for the brain. You should also keep white or blue lights (like smartphone light) far away from a sleeping person.
  • Blackout shades or eye masks can do a better job of controlling outdoor light.

The study is published in the journal SLEEP.

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About the Author

Chris Melore

Chris Melore has been a writer, researcher, editor, and producer in the New York-area since 2006. He won a local Emmy award for his work in sports television in 2011.

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