On the weekdays, we all get up for work and school and various other waking-world obligations. But on the weekends (or whenever your days off are), we're free from pressure to be functioning, vertical human beings. So, it's easier to deviate from our typical sleep schedules. Night owls, studies suggest, are especially vulnerable to falling out of sync, given that they naturally run on a later clock. But, while sleeping through Sunday morning might feel great at the time (it sure does), it can also make it harder to resume M-F rhythms.
Getting reacquainted with mother nature, however, might help us stick to workday sleep patterns, even when we don't need to. A new study from the University of Colorado, Boulder found that study participants' sleep schedules shifted over an hour earlier after camping outdoors for just one weekend. But, non-camping participants, who stayed home, fell prey to the weekend drift.
The study is an extension of previous work from the same research team, lead by Kenneth P. Wright, on circadian entrainment, referring to the synchronization of the biological clock to external cues, such as daily light-and-dark cycles. The big idea is that modern-day lighting conditions — we use artificial light at night, and reduce our bright-light intake by day — contribute to off-kilter sleep patterns and exacerbate social jet lag, which happens when your biological clock and externally imposed schedule don't line up.
In a 2013 paper, Wright's team looked at changes in melatonin levels and sleep-and-wake times for participants who camped outside for a week during the summer. In the current study, however, researchers wanted to see how going au naturel (light-wise) affected participants' circadian clocks in different seasons. So they ran two camping experiments: a two-day summer getaway, and a six-day winter trip (involving different participants).
Researchers took daily measurements of participants' melatonin levels, both during the camping trips and beforehand, when participants were still living the 2017 life. Melatonin is the drowsiness-inducing hormone produced by the pineal gland that helps regulate our sleep-wake cycles. Light suppresses melatonin, and darkness triggers its release, thereby helping our bodies and brains simmer down for sleep. By measuring melatonin, researchers were able to track changes in the duration and timing of participants' biological night, which is the period of time each day (or night, rather) when melatonin levels are high.
The two-day summer camping trip changed the timing, but not the duration, of participants' biological nights, bumping up rest schedules by 1.4 hours. Ellen Stothard, who co-authored the study, added that "people who did not go camping but instead stayed in the modern environment for the weekend had later sleep and biological timing compared to those who went camping, resulting in their clocks being timed even later after the weekend."
But winter camping made participants' biological nights both occur earlier and last longer, by 2.6 hours.
The main takeaway, according Stothard, is that "in the modern world, our clocks are timed later regardless of season, due to decreased bright light exposure during the day and increased electrical light exposure at night."
This study is part of a larger conversation about the impact of artificial light, introduced during the industrial revolution, on human sleep. Our modern-day light consumption does affect our sleep habits — this is hardly up for debate. But, what is up for debate is how humans would sleep in a world without gadgets, or even basic overhead lamps.
Some historians argue that our (roughly) eight-hour night of rest is itself a product of modernity. Without the ability to light up the night, they say, we'd sleep in two or more smaller chunks, separated by a late-night break for sex and work. But evolutionary scientists don't subscribe. While our use of technology might affect our ability to stay on schedule and get enough sleep, they say, our preference for one, long stretch of sleep evolved for good reason. Read more about the debate over "natural" rest here.