New research on the effects of daytime sunlight exposure on sleep out of UW Biology Professor Horacio de la Iglesia's lab was recently featured in UW News.

Dr. Horacio de la Iglesia and his team from the UW Department of Biology published the results of a study that tracked the sleep patterns of UW students across all four seasons – and they found something unexpected: In winter, students went to bed later in the evening and woke up later in the morning, even though (thanks to its latitude and climate) winter Seattle days are notoriously grey and overcast. The team also found that the students’ natural circadian rhythms were “pushed back” or delayed during winter, which explains their later bedtimes. 

Dr. de la Iglesia believes the reason for the delay centers on another of their findings: Students were receiving less daylight exposure in winter. Other studies have shown that daytime exposure to natural light helps “calibrate” our circadian rhythms, helping us to get tired in the evening. Dr. de la Iglesia says that getting outside in the morning and getting some light exposure, even on cloudy Seattle winter days, is the best way to keep our rhythms calibrated and prevent the type of circadian delay that they observed in this study.

A study measuring the sleep patterns of students at the University of Washington has turned up some surprises about how and when our bodies tell us to sleep — and illustrates the importance of getting outside during the day, even when it’s cloudy.

Published online Dec. 7 in the Journal of Pineal Research, the study found that UW students fell asleep later in the evening and woke up later in the morning during — of all seasons — winter, when daylight hours on the UW’s Seattle campus are limited and the skies are notoriously overcast.

The team behind this study believes it has an explanation: The data showed that in winter students received less light exposure during the day. Other research has indicated that getting insufficient light during the day leads to problems at night, when it’s time for bed.

“Our bodies have a natural circadian clock that tells us when to go to sleep at night,” said senior author Horacio de la Iglesia, a UW professor of biology. “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.”

Read the full article in UW News.