TO REAP the benefits of a good night’s rest, there are you need to consider, says at Brigham and Women’s Hospital and Harvard Medical School in Boston: how much you sleep, how well, and when.
Carving out the time to visit the land of nod is one thing, but guaranteeing good quality rest can be beyond our control. For instance, people often sleep poorly their first night in a new place. To find out why, and colleagues at Brown University in Rhode Island recently scanned people’s brains as they slept in unfamiliar places, then again when those spots had become familiar. In the first scenario, the team found that parts of one hemisphere of the brain remained active while the participants were asleep. This “first-night effect” may be an evolutionary adaptation, keeping part of your brain alert to make sure the new environment is safe. “We call this system the night watch,” Tamaki says.
Even in a familiar environment, sounds like a snuffling dog or planes overhead can , whether you’re aware of them or not. “They may force us to transition out of a deeper stage of sleep,” says Czeisler. If they wake you up, you may not realise it was a noise that roused you.
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Temperature is another neglected factor. Studies show that people with sleep disorders who wake up a lot during the night can . Counter-intuitively, this helps the body to release more heat. The cooling effect reduces the number of awakenings and also leads to . Taking a hot bath before bed can help achieve the same thing.
Perhaps the most surprising factor affecting sleep quality is the time we hit the hay. The more sleep cycles we go through (see diagram), the longer the duration of REM sleep in each cycle.
REM sleep is crucial for incorporating things we’ve learned into our existing knowledge, for regulating our emotions, and might also play a critical role in brain development. The bulk of REM sleep tends to happen in the hours just before we get up. That’s because more builds up in the second half of the night. But it’s not just to do with how long you’ve been snoozing. It’s also related to what time of day it is, says Czeisler, and whether those hours of shut-eye line up with your circadian clock.
That makes the effects of blue light on our body clocks particularly insidious – it affects sleep quality as well as quantity. Czeisler and his colleagues recently compared the sleep patterns of those who read a book on an iPad before bed with those who read print. After a few days, those using the electronic devices were getting less REM sleep, not only because it took them longer to nod off, but because their about an hour and a half later. “It sort of pushed the REM sleep later and later – and off the cliff,” says Czeisler.
Something similar happens when you have to get up unusually early. “You are most likely robbing yourself of the last two hours of sleep, so you’re going to have selectively deprived yourself of REM sleep,” says Czeisler. Setting the alarm and repeatedly hitting the snooze button can add to the problem: “You’re destroying the architecture of your sleep.”
Perhaps our wake-up routine is an opportunity to reclaim artificial light for the better. Czeisler advocates the use of light-based alarm clocks, which mimic the break of day and can help sync our circadian rhythms to our daily schedules. Light eases us out of deep sleep, leaving us less groggy – even when modern life demands that we rise before dawn.
We answer all the questions keeping you up at night in “Sleep: A user’s guide”
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This article appeared in print under the headline “What makes for a good night’s rest?”
