Why spending more time outside will help you sleep better

I imagine being a participant in some scientific trials is quite unpleasant, if not outright awful. Eating a strict, very low-calorie diet for 6 months. Restricted to 4 hours of sleep a night for two weeks. Having a cold virus squirted up your nose and waiting for the onset of illness. I wouldn’t be rushing to volunteer for these.

But, every now and again, a trial comes along that seems like fun. Like this one.

In 2013, eight lucky people were invited for a week of camping in the mountain-desert region of the Rocky Mountains in Colorado. In July. A back-to-basics experience with only the sun and campfire for light. No electronic devices. No torches. Nothing to do other than enjoy nature. That’s my kind of trial.

The point of it all was to investigate the effect on circadian rhythm and sleep of taking people out of their mostly indoor, artificially lit, urban existence, into a mostly outdoor, naturally lit, rural environment.

During the camping week, the participants went to sleep and woke up one hour and fifteen minutes earlier than they did during the week of normal urban life. But their circadian clocks (measured by melatonin onset and offset) were shunted a whole two hours earlier. There was no difference in the duration of sleep or the duration of the melatonin rhythm. But, crucially, melatonin offset (when the internal biological clock is ready for wakefulness) occurred after wake time in the urban week, but before wake time in the camping week.

In other words, in the urban environment, the participants woke up (for work, school, etc.) before their bodies were ready. Whereas in the camping environment, they woke up earlier, but in synch with their circadian clock. This likely led to an increase in morning alertness during camping, but this wasn’t measured.

The circadian clock is influenced by many things, but the most important is light exposure. More light exposure throughout the day (particularly earlier in the day) pulls the circadian rhythm forward, encouraging earlier sleep and wake times. More light exposure later in the evening pushes the circadian rhythm back, encouraging later sleep and wake times. It looks like this is exactly what was happening in the camping trial.

During the camping week, due to lots of time spent outdoors, participants’ average light exposure was more than four times greater over 24 hours than during the urban week. And it was more than three times greater in the first two hours after awakening, when the circadian clock is most sensitive to being pulled forward by light. Light exposure after sunset was three times higher in the urban, artificially lit, environment, but it was still very low relative to daytime light exposure.

I suspect, for most of us, living year-round in a tent is not practical. Or attractive. But the results from this trial are still useful. They show that getting more outdoor light exposure throughout the day, and reducing artificial light after sunset, is likely to be beneficial to sleep. It should bring your circadian clock forward, allowing you to fall asleep earlier, and wake up earlier feeling more refreshed and alert.

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