You're listening to a special archive presentation of TED Talks Daily.

This TED Talk features sleep scientist, professor, and author Matt Walker, recorded live at TED 2019.

Thank you very much. Well, I would like to start with testicles.

Men who sleep five hours a night have significantly smaller testicles

than those who sleep seven hours or more.

In addition, men who routinely sleep just four to five hours a night

will have a level of testosterone,

which is that of someone 10 years they're senior.

So a lack of sleep will age a man by a decade

in terms of that critical aspect of wellness.

And we see equivalent impairments in female reproductive health

caused by a lack of sleep. This is the best news that I have for you today. From this point,

it may only get worse. Not only will I tell you about the wonderfully good things that

happen when you get sleep, but the alarmingly bad things that happen when you don't get enough,

both for your brain and for your body. Let me start with the brain and the functions of learning

and memory, because what we've discovered over the past 10 or so years

is that you need sleep after learning

to essentially hit the save button on those new memories

so that you don't forget.

But recently we discovered that you also need sleep before learning.

And now to actually prepare your brain,

almost like a dry sponge,

...