Dr. Matt Walker

But let me come back to one night.

So that's the hormonal system as an example.

And we've already spoken, or I'll come back to it right now, the metabolic system and another hormone insulin.

What we found is that if I take you again and I limit your, and you're perfectly normal, healthy, you don't have any signs of type 2 diabetes, and I limit you to, let's say, five hours of sleep for four nights, and then I measure your ability to dispose of blood sugar, your level of blood sugar impairment is so disrupted that at that point your doctor would classify you as being pre-diabetic.

So I could take an individual and within five nights of short sleep, I can move them towards a path that's getting very close to type 2 diabetes.

And as I said, we've understood, and we, royal we, yeah.

Whenever I say we, by the way, it usually means that, well, whenever I say I did something, I mean at my center, we did something.

And when I say we did something, I mean that they did something.

That's a fair shorthand for...

for attribution.

And so there have been studies that have really decomposed exactly how that impairment in blood sugar happens.

And we mentioned that earlier in this episode.

I can also then move on to, for example, your immune system.

This is a very good demonstration.

Firstly, there's a great study done by Michael Irwin and his colleagues at UCLA.

And he took individuals, healthy individuals, and he limited them to just four hours of sleep for one single night.

And he measured levels of critical anti-cancer fighting immune cells called natural killer cells.

And what he found is that after that one night of just four hours of sleep, there was a 70% reduction in natural killer cell activity.

That is a striking state of immune deficiency.

And just to give people a reference point, these natural killer cells were...