A week's worth of camping synchs internal clock to sunrise and sunset, study finds

August 1, 2013
This is a picture of the location where the eight study participants camped for a week. Credit: Kenneth Wright

Spending just one week exposed only to natural light while camping in the Rocky Mountains was enough to synch the circadian clocks of eight people participating in a University of Colorado Boulder study with the timing of sunrise and sunset.

The study, published online today in the journal Current Biology, found that the synchronization happened in that short period of time for all participants, regardless of whether they were or night owls during their normal lives.

"What's remarkable is how, when we're exposed to natural sunlight, our clocks perfectly become in synch in less than a week to the ," said CU-Boulder integrative physiology Professor Kenneth Wright, who led the study.

Electrical lighting, which became widely available in the 1930s, has affected our internal circadian clocks, which tell our bodies when to prepare for sleep and when to prepare for . The ability to flip a switch and flood a room with light allows humans to be exposed to light much later into the night than would be possible naturally.

Even when people are exposed to electrical lights during daylight hours, the intensity of indoor lighting is much less than sunlight and the color of electrical light also differs from natural light, which changes shade throughout the day.

To quantify the effects of electrical lighting, a research team led by Wright, who also is the director of CU-Boulder's Sleep and Chronobiology Laboratory, monitored eight participants for one week as they went about their normal daily lives. The participants wore wrist monitors that recorded the they were exposed to, the timing of that light, and their activity, which allowed the researchers to infer when they were sleeping.

At the end of the week, the researchers also recorded the timing of participants' circadian clocks in the laboratory by measuring the presence of the . The release of melatonin is one of the ways our bodies signal the onset of our biological nighttime. Melatonin levels decrease again at the start of our biological daytime.

The same metrics were recorded during and after a second week when the eight participants—six men and two women with a mean age of 30—went camping in Colorado's Eagles Nest Wilderness. During the week, the campers were exposed only to sunlight and the glow of a campfire. Flashlights and personal electronic devices were not allowed.

On average, participants' biological nighttimes started about two hours later when they were exposed to electrical lights than after a week of camping. During the week when participants went about their normal lives, they also woke up before their biological night had ended.

After the camping trip—when study subjects were exposed to four times the intensity of light compared with their normal lives—participants' biological nighttimes began near sunset and ended at sunrise. They also woke up just after their biological night had ended. Becoming in synch with sunset and sunrise happened for all individuals even though the measurements from the previous week indicated that some people were prone to staying up late and others to getting up earlier.

"When people are living in the modern world—living in these constructed environments—we have the opportunity to have a lot of differences among individuals," Wright said. "Some people are morning types and others like to stay up later. What we found is that natural light-dark cycles provide a strong signal that reduces the differences that we see among people—night owls and early birds—dramatically."

Our genes determine our propensity to become night owls or early birds in the absence of a strong signal to nudge our internal circadian clocks to stay in synch with the solar day, Wright said.

The new study, which demonstrates just how strong of a signal exposure to natural light is, offers some possible solutions for people who are struggling with their sleep patterns. For example, people who naturally drift toward staying up late may also find that it's more difficult to feel alert in the morning—when melatonin levels may indicate they're still in their biological nighttimes—at work or in school.

To combat a person's genetic drift toward later nights, exposure to more sunlight in the morning and midday could help nudge his or her internal clock earlier. Also, dimming electrical lights at night, forgoing late-night TV and cutting out screen time with laptops and other personal electronic devices also may help internal circadian clocks stay more closely attuned with the solar day, Wright said.

Explore further: 3Qs: It may be daylight saving, but we're losing an hour

More information: Current Biology, Wright et al.: "Entrainment of the Human Circadian Clock to the Natural Light-Dark Cycle." dx.doi.org/10.1016/j.cub.2013.06.039

Related Stories

3Qs: It may be daylight saving, but we're losing an hour

March 12, 2012
This weekend we turn the clocks forward an hour for the return of daylight saving time, which means we lose an hour of sleep. We also have to do things an hour earlier than we did before relative to the natural light and ...

Investigational drug improves sleep disorder among the blind

June 17, 2013
An investigational new drug significantly improved a common and debilitating circadian rhythm sleep disorder that frequently affects people who are completely blind, a multicenter study finds. The results were presented Monday ...

Sleep apnea plus dim light at night increases depression, anxiety in mice

July 16, 2013
(Medical Xpress)—New research suggests the estimated 12 million Americans who have obstructive sleep apnea should take better care to sleep in a very dark room. Scientists at The Ohio State University Wexner Medical Center ...

Less sleep leads to more eating, more weight gain, research says

March 11, 2013
Sleeping just five hours a night over a workweek and having unlimited access to food caused participants in a new study led by the University of Colorado Boulder to gain nearly two pounds of weight.

Modern shift work pattern potentially less harmful to health

September 27, 2011
Recent research suggests that the modern day-day-night-night shift pattern for shift workers may not be as disruptive or as potentially carcinogenic as older, more extreme shift patterns.

Recommended for you

Anti-stress compound reduces obesity and diabetes

December 13, 2017
For the first time, scientists from the Max Planck Institute of Psychiatry in Munich could prove that a stress protein found in muscle has a diabetes promoting effect. This finding could pave the way to a completely new treatment ...

Encouraging risk-taking in children may reduce the prevalence of childhood anxiety

December 13, 2017
A new international study suggests that parents who employ challenging parent behavioural (CPB) methods – active physical and verbal behaviours that encourage children to push their limits – are likely protecting their ...

Researchers link epigenetic aging to bipolar disorder

December 12, 2017
Bipolar disorder may involve accelerated epigenetic aging, which could explain why persons with the disorder are more likely to have - and die from - age-related diseases, according to researchers from The University of Texas ...

Researchers find common psychological traits in group of Italians aged 90 to 101

December 12, 2017
In remote Italian villages nestled between the Mediterranean Sea and mountains lives a group of several hundred citizens over the age of 90. Researchers at the University of Rome La Sapienza and University of California San ...

Twitter can reveal our shared mood

December 11, 2017
In the largest study of its kind, researchers from the University of Bristol have analysed mood indicators in text from 800 million anonymous messages posted on Twitter. These tweets were found to reflect strong patterns ...

Infant brain responses predict reading speed in secondary school

December 11, 2017
A study conducted at the Department of Psychology at the University of Jyväskylä, Finland and Jyväskylä Centre for Interdisciplinary Brain Research (CIBR) has found that the brain responses of infants with an inherited ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.