Clinical benefits of sleeping in natural light

Photo Cred: Me dia/Shutterstock

By Catherine Darley, ND

Over the years, there has been an increased interest in the health benefits of nature exposure. Time in nature has been shown to improve stress levels, mental health, decision-making, and even coping with chronic pain or disease. Recently, research has shown nature can also have a profound effect on patients’ sleep.

Researchers from the University of Colorado Boulder have done a series of groundbreaking work looking nature and its impact on sleep. They first monitored people for one week on their self-selected schedule during their regular routine in the constructed environment. The participants then went tent camping for a week in the summer, still on their self-selected schedule, but with only natural light., meaning sunlight and campfires with no personal electronic devices, flashlights, or other electrical light sources.

While camping, participants got four times as much light during the day. Participants had 12.2 hours each day in light brighter than 550 lux while camping, versus only 5.1 hours while in the built environment. Analysis of light exposure during the first two hours of the day showed that participants while camping got 3074 lux, as opposed to 934 lux while in the constructed environment.

 Morning light exposure is particularly important because it entrains us to the solar day and suppresses any lingering melatonin. I think of it as a teetertotter effect, that as our melatonin is strongly suppressed in the morning, our nocturnal melatonin surge is increased and shifted somewhat earlier. On the other hand, light exposure in the evening between sunset and bedtime was higher in the built environment than while camping. This evening light causes a phase shift to later sleep-wake hours.

Melatonin patterns were strongly influenced by these different light conditions. In the built environment, melatonin began to rise about 10:30 p.m., sleep began about 12:30 a.m., and melatonin offset was about 8 a.m., which was after wake time. In naturalistic light conditions, the entire circadian melatonin pattern shifted about two hours earlier, with melatonin onset happening at about sunset, and offset just after sunrise. This melatonin offset was 50 minutes before wake time. This is clinically significant, as waking is easier and a person feels more alert when they awaken after melatonin offset.

Sleep times were shifted about 1.2 hours earlier. Although there were these significant circadian changes, total sleep time and efficiency did not change. It’s noteworthy that those people who are “night owls” had the biggest circadian shift during naturalistic lighting, suggesting their system may be more sensitive to the delaying effects of electric lighting in the built environment.

On further examination, it’s become clear that even a weekend spent in nature will improve sleep in much the same way. A second study performed by these scientists looked at two nights of summer camping compared to a weekend at home in the built environment. Again, those who were camping had four times as much daytime light exposure, and increased activity levels. The weekday to weekend sleep times were stable for the campers, although melatonin onset and offset shifted more than an hour earlier. However, those who stayed home shifted their sleep hours later than during the weekday, and melatonin onset shifted almost an hour later. This study indicates that replicating natural light conditions can be an actionable recommendation for our patients who would benefit from earlier sleep times, and an earlier melatonin rhythm.

How peoples’ sleep changes seasonally has been an open question. Conducting the study again in the winter had similar findings, though even more pronounced. Light exposure while tent camping was 13 times more during the day than in the built environment. People fell asleep about 2.5 hours earlier while camping, though wake time remained similar, so sleep total increased by 2.3 hours on average. In addition to the light changes, the cooler ambient temperature and lingering in the warmer tent probably contributed to the longer sleep periods.

During winter camping, melatonin onset was earlier, while melatonin offset was later. This resulted in a four or more-hour increase in melatonin duration compared to summer, which suggests human beings would experience seasonal changes in sleep when in natural light conditions.

Along with changes in light exposure, activity levels increased during camping, whether it be winter or summer, for a week or just a weekend. It is well-established that sleep does improve with exercise, both in our subjective experience, and on objective measures. It appears that moderate exercise has a more consistent positive effect than rigorous exercise. Increased activity should be a part of an integrative health plan for sleep patients.

Unfortunately, access to nature is not available equally to everyone. Parks are often smaller in lower economic neighborhoods and the neighborhoods tend to have more light pollution at night. There are also costs to getting out in nature for a weekend that not everyone can afford.

Several healthful lifestyle recommendations come to mind for those patients who have trouble falling asleep or being fully alert in the morning on the schedule required for their lifestyle. First, talk with patients about the importance of getting naturalistic light. I find it helpful to suggest people replicate the light exposure their great-grandparents got. When the sun goes down, it should get dark, and. Similarly. when the sun is up, it should be bright with lots of light exposure.

Encourage patients to stay active during daylight hours. People who enjoy using apps could download a lux meter and play around with the lighting in their home, aiming for many hours of bright light greater than 550 lux during the day, then reducing it to eight lux in the evening at least an hour before bedtime, or ideally from sunset on. Second, replicate these positive findings by getting naturalistic light at least on weekends or days off. Just this alone should lengthen winter sleep times, and shift it earlier throughout the year. This could have a profound effect on sleep and health over the course of time.

References

Dolezal, B.A., Neufeld, E.V., Boland, D.M., Martin, J.L., Cooper, C.B. Interrelationship between sleep and exercise: a systematic review. (2017) Adv Prev Med. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5385214/

Stothard, E.R., McHill, A.W., Depner, C.M., Birks, B.R., Moehlman, T.M., Ritchie, H.K., Guzzetti, J.R., Chinoy, E.D., LeBourgeois, M.K., Axelsson, J., Wright, K.P. Jr. Circadian entrainment to the natural light-dark cycle across seasons and the weekend. (2017) Curr Biol. Retrieved from: https://pubmed.ncbi.nlm.nih.gov/28162893/

Wright, K.P. Jr, McHill, A.W., Griffin, B.R., Rusterholz, T., Chinoy, E.D. Entrainment of the human circadian clock to the natural light-dark cycle. (2013) Curr Biol. Retrieved from: https://pubmed.ncbi.nlm.nih.gov/23910656/

About the Author

Catherine Darley, ND, is the leader in natural sleep medicine. She combines her knowledge of sleep disorders with her training as a naturopathic physician to bridge these two fields. As a naturopath, her expertise lies in providing natural and effective treatments for sleep problems. She treats people of all ages and especially enjoys working with teens and their families. She founded The Institute of Naturopathic Sleep Medicine Inc. in Seattle, which is dedicated to patient care, public education about sleep health, and consultation with high-risk populations such as first responders. Darley regularly writes articles and trains healthcare providers in the treatment of sleep disorders. She has served as adjunct faculty at Bastyr University and the National University of Natural Medicine.