Why Light at Night Can Interfere With Your Sleep

People who live with streetlight glare more likely to report sleeping trouble, study says
Why Light at Night Can Interfere with Your Sleep

Many things can impact our ability to sleep. Too much noise and too much caffeine are common culprits, but light can keep you from getting adequate rest too, recent research shows.

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People who live in more densely populated areas that are lit at night with bright street lights or signs are more likely to report trouble sleeping, suggests new research from Stanford Sleep Epidemiology Research Center in California.

Although the study doesn’t prove cause-and-effect, the scientists believe that intense outdoor illumination in the evening interferes with quality of sleep.

People with high nighttime light exposure, for example, were more likely than those in low-lit regions of the country to be dissatisfied with their sleep quantity or quality, the findings showed.

The findings were to be presented in April at the American Academy of Neurology’s annual meeting in Vancouver, Canada. Research presented at meetings typically is considered preliminary until published in a peer-reviewed journal.

Disrupting the circadian rhythm

Too much light can impact the quality of our sleep, says sleep disorders specialist Reena Mehra, MD. It’s all about our natural circadian rhythm, or our sleep/wake cycle. Our circadian rhythm causes you to feel more alert or sleepy, depending on the time of the day, according to the National Sleep Foundation.

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Your levels of melatonin, a sleep-promoting hormone, rise in the evening, the foundation says. Exposure to light delays the release of that hormone, the foundation explains.

“The light exposure is, in essence, somewhat disrupting our circadian rhythm,” Dr. Mehra says. “This is especially true at night because you don’t want that bright light exposure at night when you’re supposed to be asleep.”

Bright light not only keeps you alert, but it is the strongest external cue that we have to signal our circadian rhythm, Dr. Mehra says.

“We take cues from the intensity of light and the timing of light and that’s what helps us sleep and wake,” she says.

More light, less sleep

The research, which looked at data on the sleep habits, quality of sleep and medical and psychiatric disorders of more than 15,000 people in interviews over eight years.

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The researchers used data from the Defense Meteorological Satellite Program to determine the amount of light people were exposed to at night. Findings showed that those who had light exposure while sleeping got about 10 minutes less sleep per night. They also were more likely to report fatigue, wake up confused during the night, and have excessive sleepiness and impaired functioning during the day.

Those who lived in cities with a population of 500,000 or more were exposed to street lights three to six times more intense than those who lived in lesser-populated areas.

For those who live near bright street lights, taking preventative measures is a good idea, Dr. Mehra says.

“Blackout drapes are great and can be very effective especially for  shift workers who work at night,” Dr. Mehra says. “When shift workers go home and then try to sleep, it’s hard to do if the sun is streaming in through the windows.”

In addition to blackout curtains or shades, Dr. Mehra says that a sleep mask that covers the eyes also can be effective for blocking out unwanted light.

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