Great outdoors resets biological clocks

It turns out that all that malarkey from our parents about turning out the light at night and then getting fresh air and sunshine during the day was right, at least according to a team of researchers from the University of Colorado’s Sleep and Chronobiology Laboratory.

A research team from the lab spent a week camping out with volunteers in tents in Colorado’s Rockies to see what effect, if any, the experience might have on an individual’s biological clock. The effect was a wake-up call, especially for night owls.

Midsummer light-dark cycle

The study showed that, when exposed to natural light without the interference of artificial lights, humans’ internal biological clocks will tightly synchronise to a natural, midsummer light-dark cycle, with internal biological night occurring at sunset and the end of the internal biological night occurring before wake time just after sunrise. Unsurprisingly, the effects were most noticeable on the group’s ‘night owls’, with campers’ body clocks quickly shifting back by 2 hours on average.

The results show that a short camping trip could be a powerful curative for those who have trouble going to sleep at night and then waking up for work or school in the morning. From a scientific point of view, the researchers say it is the first time we have begun to quantify and understand how modern light exposure patterns contribute to late sleep schedules and may disrupt sleep and circadian clocks.

“The electric light is one of the most important human inventions. Sleep and other daily rhythms in physiology and behaviour, however, evolved in the natural light-dark cycle, and electrical lighting is thought to have disrupted these rhythms.

Delayed circadian clock

“Here we show that electrical lighting and the constructed environment is associated with reduced exposure to sunlight during the day, increased light exposure after sunset and a delayed timing of the circadian clock as compared to a summer natural 14 hr 40 min:9 hr 20 min light-dark cycle camping,” the researchers write in their published paper.

For the experiment, lead researcher Professor Kenneth Wright and his colleagues first studied the internal circadian timing of eight adults (with an average age of 30) by monitoring the fluctuations in the hormone melatonin (a hormone that prepares the body for sleep) and exposure to light as monitored by a wrist unit, during 1 week of routine work, school, social activities and self-selected sleeping schedules with their usual exposure to electrical lighting.

They then took those same people out camping for a week, with sunlight and campfires only – no flashlights or even smartphones allowed – but they could sleep according to any schedule they chose.

Their studies showed that a typical, modern environment causes about a 2-hour delay in the circadian clock. People in an artificially lit environment tended to stay up until after midnight and to wake up around 8:00am. However, after a week of natural lighting, where the volunteers were exposed to around four times as much light as they received in their normal routines, all measures of circadian timing shifted 2 hours back, and sleep schedules followed, even as the total time spent sleeping stayed about the same.

Shifts in melatonin levels

In a press release from the journal Current Biology, the researchers also noted a paradox in brain arousal. “Melatonin levels rise in the early evening and then taper off in the morning before a person wakes up. In our modern world, melatonin levels tend to decrease to daytime levels about 2 hours after we wake up. In other words, our biological night extends past our wake time and contributes to why many of us are at our sleepiest soon after we wake up in the morning. With exposure to natural light, that decrease in melatonin shifts to the last hour of sleep time, then brain arousal rises earlier, likely helping people feel more alert in the morning.”

Professor Wright notes that, although we can’t all go camping, other strategies could help. “Our findings suggest that people can have earlier bed and wake times, more conducive to their school and work schedules, if they were to increase their exposure to sunlight during the day and decrease their exposure to electrical lighting at night,” he says.

So, if you’re keen to change your sleeping habits and feel more alert in the morning, go for a morning walk, keep your shades open at work and step outside for lunch. In the evening, keep the lights down low and turn the computers and TVs off an hour before bedtime.

The research was published in the 7 September 2013 edition of the journal Current Biology.