How caffeine and alcohol affect your sleep

Caffeine wakes you up, and alcohol makes you nod off, right? It's not that simple. Sleep scientist Matt Walker takes us into the eye-opening ways that these drinks affect the quantity and quality of our sleep.

Many of us like to start the day
with a cup of coffee

and perhaps end the day
with a glass of wine

or some other kind of alcoholic drink.

But it turns out
that these two substances,

alcohol and caffeine,
can have surprising impacts on our sleep.

[Sleeping with Science]

(Music)

Let's start with caffeine.

Caffeine is in a class of drugs

that we call the psychoactive stimulants.

And everyone knows that caffeine
can make them more alert.

It can wake them up.

But there are at least two additional,

hidden features of caffeine

that some people may not be aware of.

The first is the duration
of action of caffeine.

Caffeine, for the average adult,

will have what we call a half-life

of about five to six hours.

What that means is that
after about five to six hours

50 percent of that caffeine that you had

is still circulating in your system.

What that also means
is that caffeine has a quarter-life

of about 10 to 12 hours.

In other words, let's say
that you have a cup of coffee

at 2pm in the evening.

It could be that almost
a quarter of that caffeine

is still swilling around
in your brain at midnight.

And as a result, it can make
it harder for an individual

to fall asleep or even stay asleep soundly

throughout the night.

So that's the first feature of caffeine.

The second issue with caffeine

is that it can change
the quality of your sleep.

Now some people will tell me

that I'm one of those individuals

who can have an espresso with dinner,

and I fall asleep fine,
and I can stay asleep.

But even if that's true, it turns out

that caffeine can actually
decrease the amount

of deep, non-rapid eye movement
sleep that we have,

stages three and four of non-REM sleep.

That's that sort of
restorative deep sleep.

And as a consequence,
you can wake up the next morning,

and you don't feel refreshed,

you don't feel restored by your sleep.

But you don't remember waking up,

you don't remember
struggling to fall asleep,

so you don't make the connection,

but nevertheless
you may then find yourself

reaching for two cups of coffee
in the morning to wake up

rather than one.

So that's caffeine,
but now let's move on to alcohol,

because alcohol is perhaps one

of the most misunderstood
sleep aids out there.

In fact, it's anything but a sleep aid.

And it can be problematic for your sleep

in at least three different ways.

First, alcohol is in a class of drugs

that we call the sedatives.

But sedation is not sleep.

And studies teach us that those two things

are really quite different.

Sedation is a case

where we're simply
switching off the firing

of the brain cells,
particularly in the cortex.

And that's not natural sleep.

In fact, during deep
non-rapid eye movement sleep,

for example, the brain has
this remarkable coordination

of hundreds of thousands of cells

that all of a sudden fire together,

and then they all go silent,

and then they all fire together,
and then they go silent,

producing these big, powerful brainwaves

of deep non-REM sleep.

And so that's the first way

in which alcohol can be problematic.

We're mistaking sedation for deep sleep.

The second problem with alcohol

is that it can actually
fragment your sleep.

Alcohol can actually trigger
and activate during sleep

what we call the fight or flight branch

of the nervous system,

which will therefore
wake you up more frequently

throughout the night.

And alcohol can even increase the amount

of alerting chemicals
that are released by the brain,

once again fragmenting your sleep.

The third and final issue
with alcohol and sleep

is that alcohol can actually block

your rapid eye movement sleep,
or your dream sleep.

And as we'll learn in subsequent episodes,

REM sleep, or rapid eye
movement sleep, dream sleep,

provides a collection of benefits,

things such as your emotional

and mental health, even creativity.

Now I'm not here
to tell anyone how to live.

I don't want to be puritanical.

I'm just a scientist.

What I want to try and do is provide you

with the information
about the relationship

between caffeine and alcohol on your sleep

so then you can make an informed choice

as to how best you want to live your life

when you're trying to
prioritize your sleep health.