Dr. Matt Walker

Think of them almost like the secret service agents of your immune system.

These natural killer cells, they are very good at identifying dangerous, unwanted elements in your body like cancer and going after them and destroying them.

So you wish for a very virile set of these immune assassins in your body at all times.

And if you're not getting sufficient sleep, that may not necessarily be the case.

We also know that if you are not getting sufficient sleep in the week before you get your flu shot, and this is just another example of how sleep is critical for your immune system.

If you're not getting that sleep in the week before you get your flu shot, you produce less than 50% of the normal antibody response, therefore rendering that flu shot largely ineffective in terms of vaccinating you.

We also know that if you're not getting sufficient sleep on average,

let's say that you're getting less than six hours of sleep or less on average, you're almost three times more likely to develop the common cold, common flu.

And I know that you, at the time of us recording this, you've released some fantastic content about the flu and the rhinovirus in particular.

So that's a good demonstration of your immune system.

We also know that it's not just that, it's also your cardiovascular system that suffers when you're not getting sufficient sleep.

And here again, the data I think is very strong.

Cardiovascular disease writ large, including stroke and heart attack.

And there is one study that I think illustrates this.

And granted now in terms of the replication, the effect sizes may not be as big, but the study was interesting.

They didn't do something radical like depriving you of sleep for an entire night, nor did they just limit you to five hours of sleep for four nights.

There is a global sleep experiment that has performed on about 1.65 billion people across 70 countries twice a year, and it's called Daylight Savings Time.

Now in the spring, when we lose an hour of sleep, what they observed in that paper was a 24% relative increase in heart attack risk the following day.

Yet in the autumn, in the fall, when you gain an hour of sleep, there was a 21% reduction.

So it's bi-directional.