Humans have been fighting our internal clocks ever since we invented sitting around a campfire. We have powerful natural rhythms that keep us on a 24-hour cycle; if you’ve ever been steamrollered by jet lag after an intercontinental flight, you know how powerful those rhythms are. But we muffle them with caffeine, alarm clocks, and electric lights. It’s easy to undo the damage, though. One weekend of camping can do the trick—and it’ll even cure your case of the Mondays.

In 2013, researchers at the University of Colorado Boulder looked at how a weeklong summer camping trip affected people’s rhythms. They found that campers’ internal clocks shifted to sync up with the sun. People fell asleep earlier, and woke up earlier, than they did in their regular lives. But the researchers had more questions. How quickly could people’s clocks adjust? Was a whole week of camping really necessary? What would happen if they sent people camping in the winter, instead of the summer?

The researchers recruited five intrepid men and women for a winter camping trip. First, the group spent six days following their regular schedules while wearing devices on their wrists that monitored when they slept and woke, as well as how much light they were exposed to. Subjects also came into the lab for a day so researchers could gather their saliva every hour. They tested the saliva for melatonin, a hormone that rises and falls each day in sync with our internal clock.

Then, still wearing their wrist monitors, the group headed into the Rockies together for six chilly days. The campers decided for themselves when to go to bed and when to crawl out of their tents each morning. But they weren’t allowed to use electronics, flashlights or other artificial lights. (Campfires were OK). After the camping trip, they returned to the lab to have their melatonin checked again.

Just as in their earlier summertime study, the researchers saw that campers’ circadian rhythms changed dramatically. Subjects went to sleep about 2.5 hours earlier than they had in their regular lives, and woke up around the same time they usually did. Their melatonin cycles had shifted to match.

If subjects were just sleep deprived, and catching up on lost sleep during their trip, they ought to have slept less as the week went on. Instead, they slept more. The researchers note that some of that extra sleep may have come from reluctance to leave a warm sleeping bag for the cold outdoors.

Comparing the results to their earlier study, the researchers found that people going about their regular lives had similarly timed melatonin cycles, whether it was winter or summer. But for campers, melatonin cycles looked different in different seasons—in the winter, the nighttime part of the melatonin cycle was longer. That suggests people’s natural rhythms are flexible. When people live without artificial lights, their internal clocks adjust to summer or winter hours.

To find out how quickly a dose of outdoor living can reset someone’s clock, the researchers sent another group of subjects on a weekend camping trip in the summer. This time nine campers headed out to enjoy the Rockies, while five stayed home. Unlike in the earlier studies, this group got to use headlamps and flashlights (something the winter campers probably would have appreciated when they had to pee in the middle of the night).

Even this quick camping trip was enough make a difference. Subjects went to bed and woke up at about the same times they did during the week. But their melatonin levels started to rise about 1.5 hours sooner in the evening, indicating that their internal clocks had shifted earlier.

Meanwhile, people who’d stayed home experienced a shift too: They slept and woke up about an hour later over the weekend than during the week. Their melatonin cycles also shifted later.

The authors says this can be a result of staying out late and sleeping in. These normal weekend behaviors can push people’s clocks later and cause “social jet lag,” or feeling extra bummed about your alarm going off on Monday morning.

Headlamps or no, dark nights weren’t the only difference that campers experienced compared to their regular lives. The days were brighter, too. Summer campers were exposed to about four times more light during waking hours than in their regular lives. And winter campers experienced more than 13 times more light than they did in their electrically lit homes and offices.

Aside from making you more chipper on Mondays, the researchers say, keeping an earlier schedule of sleeping and waking might help with daytime sleepiness in general. It could also improve your cognitive performance, mood, and physical health. At the very least, a weekend camping trip will make you grateful that your home bathroom has a light switch.

Image: Emilian Robert Vicol (via Flickr)

Stothard ER, McHill AW, Depner CM, Birks BR, Moehlman TM, Ritchie HK, Guzzetti JR, Chinoy ED, LeBourgeois MK, Axelsson J, & Wright KP Jr (2017). Circadian Entrainment to the Natural Light-Dark Cycle across Seasons and the Weekend. Current biology : CB, 27 (4), 508-513 PMID: 28162893