Hoping to improve the quality of your sleep? You might think living like a bat and spending more time in darkness would help.
However, a new study suggests just the opposite. It found students at the University of Washington tended to fall asleep later at night and wake up later in the morning during winter, when there was less daylight. That surprised researchers who expected to find that students stayed up later in the summer when there were more hours of sunlight.
Study authors concluded that the lack of exposure to daylight hampered the students’ ability to get quality sleep, according to findings published in the Journal of Pineal Research. Previous research has suggested such a link between insufficient exposure to daylight and difficulty falling asleep.
In a summary of the findings, the study’s senior author, Horacio de la Iglesia, a professor of biology at the University of Washington, says:
“Our bodies have a natural circadian clock that tells us when to go to sleep at night. If you do not get enough exposure to light during the day when the sun is out, that ‘delays’ your clock and pushes back the onset of sleep at night.”
During the research, students wore wristbands that measured their sleep patterns and exposure to light. The season itself did not impact the total amount of time students slept.
However, during the winter, students went to bed on average 35 minutes later and woke up 27 minutes later than in the summer months.
Researchers were not expecting that result, especially given that Seattle gets nearly 16 hours of sunlight on the summer solstice but just about eight hours of sunlight on the winter solstice.
In trying to explain the results, researchers concluded something was “pushing back” the students’ circadian cycles during the winter.
According to the summary of the research findings:
“For most humans, including college students, the innate circadian cycle governing when we’re awake and asleep runs at about 24 hours and 20 minutes — and is ‘calibrated’ daily by input from our environment. For UW students in the study, sleep data indicated that their circadian cycles were running up to 40 minutes later in winter compared to summer.”
Researchers noted that the time of day you are exposed to light plays a big role in your sleep pattern. Exposure to light early in the day advances your clock, making you tired earlier in the evening.
On the other hand, exposure to light late in the day or early evening delays your clock. That means you are more likely to feel tired later. De la Iglesia concludes:
“Many of us live in cities and towns with lots of artificial light and lifestyles that keep us indoors during the day. What this study shows is that we need to get out — even for a little while and especially in the morning — to get that natural light exposure. In the evening, minimize screen time and artificial lighting to help us fall asleep.”
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