On Monday morning, it’s often painful to peel open one’s eyelids and roll out of bed. But spending more time out in the sun, even just a quick weekend camping trip, can be enough to send us to bed earlier, according to a new study in the journal Current Biology.
“After a weekend of camping, our clocks are timed perfectly in synch with the sunrise and sunset,” says study senior author Kenneth Wright, a sleep researcher at the University of Colorado Boulder.
Resetting one’s sleep clock could not only make Monday mornings easier, but could help prevent the negative health affects associated with late bedtimes, such as increased sleepiness, worse driving and school performance, and heightened risk of diabetes, obesity, and substance abuse.
The study also found, for the first time, that humans are sensitive to seasonal changes in the light-dark cycle just like other animals: In the absence of electrical light, we go to bed earlier on short winter days and stay up later on long summer evenings.
In a previous study, Wright and colleagues found that modern electrical lighting has edged human sleep-wake cycles later by a whopping two hours. The combination of less exposure to bright sunlight during the day and increased electrical light in the evenings has delayed people’s internal clocks, sending us to bed later and making it harder to wake up with the sun to get to work or school.
This was not your typical science experiment: First, Wright’s team took a group of adults camping in the Rocky Mountains in Colorado for a week during the summer. Participants were exposed only to natural light: sunlight, moonlight and campfire. No iPads, cell phones, or even flashlights were allowed. And they slept in tents, going to bed and waking up on their own schedules.
Before and after camping, the scientists took a series of saliva samples to measure fluctuations in the participants’ levels of melatonin, a hormone that can be used to detect the time of one’s internal biological clock. Melatonin levels rise before the onset of the sleep cycle, and fall as one begins to wake.
Next, the scientists took a new set of volunteers camping on some of the darkest, longest nights of the year during the chilly Colorado winter. This time, the team found that camping was enough to send people to bed 2.5 hours earlier than their typical schedule — and help them sleep 2.3 hours longer than normal each night. Then, on a final trip, the team found that even a quick weekend of summer camping was enough to rapidly shift people’s internal clock earlier.
These changes were driven in large part to sunlight exposure, says Wright. Light influences the master clock in our brains, which directs melatonin levels when to rise and guide our bodies toward sleep. And when you’re outside, you’re exposed to a lot more light: Modern indoor electrical lighting illuminates with the strengths of about 200 lux, while the sun shines 100,000 lux on a bright day and even 10,000 lux on a cloudy day.
“If your goal is to achieve earlier bedtimes and wake times — and be more alert in the morning — then being more in sync h with the natural light cycle is expected to help that,” says Wright.
That doesn’t mean you have to go camping (although that appears to be a good quick fix). Simply getting more sunlight exposure — such as starting the day with a walk, exercising outside during lunch, or even sitting by a window while you work — and reducing exposure to electrical lighting at night, can help your body achieve earlier bedtimes.
The studies were small — just five people participated in the winter camping and nine in the summer — but the effect on sleep cycles was large. Next, Wright hopes to study how natural light-dark exposure might affect the biological clock of people with sleeping disorders.
Megan Scudellari is a Boston-based science writer. She can be reached at email@example.com.