Maybe your friend who wakes up at 5 a.m. every day is kind of 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 chronotype, or preferred sleeping pattern.
Scientists study chronotypes by tracking when people go to sleep on days when they don't have to go to work or to school.
This chart shows the mid-point of people's sleep on those free days.
If you go to bed around 11 p.m. and get up around 7 a.m., you have an average chronotype.
A very small number of people on either end of the chart have either very early or very late chronotypes.
But even those of us who are just slightly behind the average chronotype can wake up feeling 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.
So 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 after a free day can feel 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, your SCN tells the pineal gland to start producing melatonin around 9 p.m., that makes you sleepy.
Around 10:30, your colon starts suppressing bowel movements.
Your body temperature drops to its lowest point around 4:30 a.m., and your blood pressure reaches its highest point around 6:45 a.m., so you're at your most alert around 10 a.m..
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 this 24-hour cycle.
This 7 day time-lapse of the SCN shows these clock genes releasing proteins every 24 hours 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, and studies have found similar mutations in hamsters with early chronotypes.
But when scientists took out these hamsters' SCN, their body clock, and replaced them with the SCN of a normal hamster, 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, you know, it's not this nuisance, it's this kind of fundamental part of life.
Maybe some late sleepers are lazy, sure. But the rest have been sorely misunderstood.