Exposure to daylight helps you sleep better at night, study finds

Insufficient sun exposure during the day can lead to sleep problems at night, according to a new study that recommends people get out in the sun in the morning, even if it’s for “a little while”.

The research, published last week in the Pineal Research Journal, used wrist monitors to track the sleep and light exposure patterns of over 500 undergraduate students at the University of Washington (UW) in the United States from 2015 to 2018.

Scientists have found that students fall asleep later in the evening and wake up later in the morning, mostly in winter when their hours of daylight exposure on campus are limited.

“Our body has a natural circadian clock that tells us when to go to sleep at night. If you aren’t exposed to enough light during the day when the sun is out, it ‘lags’ your clock and delays the onset of sleep later in life. night,” study lead author Horacio de la Iglesia, a UW biology professor, said in a statement.

Scientists found that while students got roughly the same amount of sleep each night, regardless of season, in winter they went to bed an average of 35 minutes later and woke up 27 minutes later than in summer.

“We expected students to get up later in the summer because of all the light available during that season,” Dr. de la Iglesia said.

Researchers suspect something is “pushing back” pupils’ circadian cycles in winter.

They say the body’s internal clock that governs when people are awake and asleep runs around 24 hours and 20 minutes, “calibrated” daily by input from our environment.

However, the study suggests that these circadian cycles for UW students ran up to 40 minutes later in winter compared to summer.

“Light during the day – especially in the morning – causes your clock to move forward, so you’ll tire earlier in the evening, but light exposure late in the day or early at night will set your clock back, pushing the timing back. where you’ll feel tired,” says Dr. de la Iglesia.

“Ultimately, when you fall asleep is a result of the push and pull between these opposing effects of light exposure at different times of the day,” he added.

The new research also suggests that daylight exposure may have a greater impact than evening light exposure.

He found that each hour of daylight “lifted up” the students’ circadian phases by about 30 minutes.

While each hour of evening light, such as that from indoor sources like lamps, delayed the phases of the biological clock by an average of 15 minutes, the scientists found.

“It’s this push-and-pull effect. And what we found here was that since the students weren’t exposed to enough daylight in the winter, their circadian clocks were lagged compared to the summer,” Dr. de la Iglesia explained.

With increasing numbers of people around the world moving to live in cities and towns with artificial light and lifestyles that keep them indoors during the day, researchers are calling for these city dwellers to get out, “even for a little while and especially in the morning”, to get exposure to natural light.

“In the evening, minimize screen time and artificial lighting to help us fall asleep,” Dr. de la Iglesia added.

“Our results show that although sleep time is strongly synchronized with social time, sleep delay is evident during the winter months. They also suggest that daily exposure to daylight is essential to prevent this delayed phase of the circadian clock,” the researchers wrote in the study.

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