That’s because when you need sleep depends on what’s called your chronotype—your body’s natural inclination towards certain times of day. And that, he explained, is largely genetic.
“Society is currently biased toward the morning types,” he said at the symposium, “as we have a notion that the type A type should be rewarded.” And unfortunately, he acknowledged, “we stigmatize the night owls.”
That’s particularly true in light of society’s tendency toward what Walker called “competitive undersleeping,” or bragging about, say, awaking at dawn or only needing four hours of shut-eye. What’s implied with that, he says, is that idea that “I’m so busy and I’m so important, which is why I’m awake so much.” While such “genetic short sleepers” do exist, they are rare—rarer than the probability of being struck by lightning, says Walker. In general, people need between seven to nine hours of rest a night.
There’s also the misunderstanding that when night owls stay up late and then wake up early, others assume that they must just need less sleep. But really, he explains, “They are being forced to sleep at the wrong time.”
Below, everything you need to know about your chronotype, and how to get enough sleep in spite of what the rest of the world tells you.
“Chronotype describes an individual’s preferred timing of sleep and activity,” Walker explains, noting that it’s about 40 to 50% genetically influenced and shifts naturally with age—becoming later in adolescence and earlier in adulthood. It’s not to be confused with circadian rhythm, or your body’s 24-hour internal clock, which is similar from person to person—and which chronotype exists within.
Not sleeping in harmony with your chronotype, Walker explained, is when you run into trouble—not only with exhaustion, but disease.
“All of this evidence, to me at least, impresses the fact that when we do not sleep in harmony with our chronotype, the ensuing sleep disruption that unfolds has consequences,” Walker tells Fortune.
“Chronotype-related risks can often be mitigated if you can just nudge yourself a little closer to your natural type,” Walker advises. “I know that’s hard. But even 15 or 20 minutes is a great start, and night after night, that’s like compounding interest on a good investment!”
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