Dr. Matt Walker

Throughout the lifespan.

When we're adults, we critically need it.

Yes.

You're right, it's an and gate.

So it's nighttime-ness does help, but sleep helps perhaps significantly more.

Meaning that I can have you experience the nighttime, but I can deprive you of sleep and selectively of deep non-REM sleep.

and I can markedly impair your growth hormone release.

Correct.

So we can do it one of two ways.

So my way is to say, I keep you on a diurnal, nocturnal sort of schedule where you're awake during the day and you sleep at night, but I'm going to selectively deprive you of just your deep sleep at night.

So you're still sleeping and you're still spending the night timeness in bed.

which is not the shift work version, but I can block or not block.

I can significantly reduce your growth hormone because I selectively deprived you of sleep.

Or I can do the opposite, which is the shift work approach, which is I'm not going to deprive you of sleep.

You're going to sleep during the day.

but now I have held sleep constant.

So in my version, I have held nighttime-ness constant and I've manipulated sleep.

In your version, the shift worker, we've done the opposite.

We've held sleep constant, thus sleeping during the day, but we've manipulated nighttime-ness.

And now, as you said, yes, they will release some growth hormone, even though that's not the natural time on the 24-hour clock when we would see growth hormone released.