This study, published in the journal Current Biology, was divided into two different experiments. For the first the research team recruited 14 volunteers, nine went camping in the wilderness for the weekend and five stayed home. Results showed that upon return the camper's melatonin had shifted by almost an hour and a half, supporting an earlier bedtime.
What's most surprising about these results is that it only took one weekend to reset the body's internal clock, which can get confused by our crazy schedules and the artificial light blaring from our cell phones and computers long after the sun has gone down.
The second part of the study sent five people on a six day camping trip—without flashlights, cellphones, or other gadgets. Totally at the mercy of the sun and moon the campers went to sleep about two and a half hours before they would have at home. They also slept around ten hours a night, compared to their at-home average of seven. Monitors also showed that they were exposed to about 13 times more light than they would normally get and melatonin shifted by about two and half hours by the time they got back.