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Natural office daylight improves overall health and sleep quality

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Workers with windows are more physically active and have longer sleep duration

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A new study from Northwestern Medicine and the University of Illinois at Urbana-Champaign examined the impact of daylight exposure on the health of office workers from the perspective of subjective well-being and sleep quality as well as actigraphy measures of light exposure, activity, and sleep-wake patterns.

This new study included 49 day-shift office workers; 27 workers working in windowless environments and 22 comparable workers in workplaces with significantly more daylight.

Well-being of the office workers was measured by Short Form-36 and sleep quality was measured by Pittsburgh Sleep Quality Index (PSQI).

In addition a subset of 21 office workers; 10 workers in windowless environments and 11 workers in workplaces with windows) had actigraphy recordings to measure light exposure, activity, and sleep-wake patterns.

Employees with windows in the workplace received 173% more light exposure and slept an average of 46 minutes more per night than employees who did not have the natural light exposure in the workplace. Workers with windows at the workplace had more light exposure during the workweek, a trend toward more physical activity.

Workers without windows had poor scores on life quality measures due to physical problems and vitality as well as poorer outcomes on measures of overall sleep quality and sleep disturbances compared to office workers with windows.

According to Dr. Phyllis Zee, MD, Associate Director, Center for Sleep & Circadian Biology, professor Northwestern University Institute for Neuroscience and senior author of study "There is increasing evidence that exposure to light, during the day, particularly in the morning, is beneficial to your health via its effects on mood, alertness and metabolism.” "Workers are a group at risk because they are typically indoors often without access to natural or even artificial bright light for the entire day. The study results confirm that light during the natural daylight hours has powerful effects on health."

Dr. Mohamed Boubekri, PHD, associate professor of architecture at the University of Illinois at Urbana- Champaign and co-lead author of the study commented "Architects need to be aware of the importance of natural light not only in terms of their potential energy savings but also in terms of affecting occupants' health.”

Dr. Boubekri noted that a simple design solution to augment daylight penetration in office buildings would be to make sure the workstations are within 20 to 25 feet of the peripheral walls containing the windows. "Daylight from side windows almost vanishes after 20 to 25 feet from the windows," he said.

Ivy Cheung, co-lead author and Ph.D. candidate in neuroscience in Zee's lab at Northwestern commented “Light is the most important synchronizing agent for the brain and body. “ "Proper synchronization of your internal biological rhythms with the earth's daily rotation has been shown to be essential for health."

Also, people who get more light during the day may sleep better at night, which can also help improve health, Zee noted.

This study is published in the Journal of Clinical Sleep Medicine.