Late sleepers get a bad rap. Maybe your friend who wakes up at 5 a.m. every day is a little quirky, but I bet they’re
productive. Your friend who wakes up at 11 every day, what do you think about them? But it turns out, sleeping late isn’t just a preference or a bad habit. Research is showing
that our bedtime could be coded into our DNA. Each of us has an internal clock, but my clock
isn’t necessarily in sync with yours. That’s because we all have our own chronotypes,
or preferred sleeping patterns. Scientists study chronotypes by tracking when
people go to sleep on days they don’t have to go to work or school. This chart shows the the mid-point of people’s
sleep on those free days. If you go to bed around 11 pm and get up between around 7 am, you have an
average chronotype. A very small number of people on either end of the chart have very early or very late chronotypes. But even those of us who are just slightly
behind the average chronotype can feel jet-lagged every day.
If you have an average chronotype, you’re generally getting the same amount of sleep on both free days and work days. Your sleep schedule fits with society’s
schedule. But the later your chronotype, the bigger
the difference between the amount of sleep you get on free days versus work days. So going back to a work day after a free day
is like flying over several time zones. And to understand why, you need to look at the master clock in our body. It’s a bundle of neurons called the Suprachiasmatic Nucleus, or SCN.
If you have a normal chronotype you SCN tells your pineal gland to start
producing melatonin around 9 pm, that makes you sleepy. Around 10:30, your colon starts suppressing bowel movements. Your
body temperature drops to its lowest point around 4:30 am, and your blood pressure reaches
its highest point around 6:45 am, so you’re at your most alert around 10 am
But for people with late chronotypes, all this stuff happens later in the day.
And there’s not much they can do about it. That’s because inside the neurons that make
up the SCN, scientists have discovered something called clock genes.
These genes turn on and off throughout the day to keep your body on a 24-hour cycle.
This time-lapse of the SCN shows these clock genes releasing proteins every 24 hours for
a week like…clockwork Researchers who study families of extreme
early-risers show that many of them share the same mutation on one of these clock genes.
Studies have found similar mutations in hamsters hamsters with early chronotypes. But when scientists took out these hamsters’ SCN, their body clock, and replaced them with the SCNs of normal
hamsters, they still woke up and went to sleep super early.
That’s because the SCN isn’t our only biological clock.
you also have all these little clocks in every single cell of your body In the early-rising hamsters, these clocks
in the body preserved the early chronotype, even after the brain’s SCN was taken out.
And for humans, this helps explain why it’s nearly impossible for late sleepers to adjust
to society’s schedule…the cells in their bodies literally won’t let them. And that’s
a problem. In one study, researchers took healthy people and messed with their sleep schedules. After
three weeks, they had early signs of diabetes. People with late chronotypes are also more
likely to be smokers and to develop depression. and maybe that should change the way we think
about sleep, it’s not this nuisance, it’s this fundamental part of life. Maybe some late sleepers are lazy, sure. But
the rest have been sorely misunderstood.