Dr. Matt Walker

Not necessarily because it makes you look longingly at people's necklines and want to bite in, which is great if you're into that, but it's really simply about it's releasing melatonin, which tells the brain, my goodness, it's nighttime.

But if you've got bright light on, you come from your office, you're driving home, so you've got artificial light during the day, which is probably not strong enough to stimulate you and bring you awake.

You come home and you've got again, bright light

but it's still strong enough now to prevent the release of melatonin, you start to shift in your timing and you may have problems with your sleep.

So that's the second piece of advice.

I would love to ask you about that morning light too and the alertness benefits.

I'm, as a sleep researcher, more focused on the evening component of light and decreasing it, but you've done a great job.

I don't know if there's anything...

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.