Dr. Matt Walker

And what I like about, firstly, your mention of cortisol, you described how cortisol is rising in the morning, and that's a great thing, and it is a good thing.

And in the evening, it's starting to drop.

And if you look right around your prototypical bedtime, and we're going to speak later in this episode as to what your real natural bedtime is versus the one that you may be taking right now.

It's very interesting.

Cortisol will almost hit its lowest point, something that we call its nadir.

It's the lowest point in that trough of its decline, right around the time when you should be sleeping.

However, there's a great study that looked at people with insomnia.

And in subsequent episodes, we'll discuss this too.

But one of the ways that we think about or conceptualize insomnia is in two different flavors, sleep onset insomnia, I can't fall asleep, and sleep maintenance insomnia, I wake up, I can't get back to sleep.

And what they looked at was essentially cortisol levels.

They had a catheter in the arm and they were sampling it from the bloodstream and they were able to do that every 30 minutes.

So it's a little bit like time lapse photography and you're getting a data point every 30 minutes across the 24 hour period.

looking at cortisol across now a full 24 hour period.

And sure enough, when you look at healthy controls who can sleep well and insomnia patients, they look almost identical across the day.

But then when it comes to falling asleep right around that bedtime period, the healthy controls are going all the way down.

The insomnia patients go down and down and down, and then they have a rise back up right around that sleep onset period.

And then they start to drop back down again, just as the control group.

But then they also often will have a spike in the middle of the night, which then comes down.

And then both of them are staying low throughout the early morning period.

And then it starts to rise back up.