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

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and perhaps end the day
with a glass of wine

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or some other kind of alcoholic drink.

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But it turns out
that these two substances,

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

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[Sleeping with Science]

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(Music)

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Let's start with caffeine.

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Caffeine is in a class of drugs

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that we call the psychoactive stimulants.

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And everyone knows that caffeine
can make them more alert.

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It can wake them up.

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But there are at least two additional,

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hidden features of caffeine

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that some people may not be aware of.

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The first is the duration
of action of caffeine.

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Caffeine, for the average adult,

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will have what we call a half-life

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of about five to six hours.

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What that means is that
after about five to six hours

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50 percent of that caffeine that you had

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is still circulating in your system.

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

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of about 10 to 12 hours.

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

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at 2pm in the evening.

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It could be that almost
a quarter of that caffeine

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is still swilling around
in your brain at midnight.

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

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to fall asleep or even stay asleep soundly

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throughout the night.

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So that's the first feature of caffeine.

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The second issue with caffeine

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is that it can change
the quality of your sleep.

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Now some people will tell me

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that I'm one of those individuals

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who can have an espresso with dinner,

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

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But even if that's true, it turns out

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that caffeine can actually
decrease the amount

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

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stages three and four of non-REM sleep.

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That's that sort of
restorative deep sleep.

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

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and you don't feel refreshed,

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you don't feel restored by your sleep.

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But you don't remember waking up,

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you don't remember
struggling to fall asleep,

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so you don't make the connection,

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but nevertheless
you may then find yourself

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

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rather than one.

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

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because alcohol is perhaps one

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of the most misunderstood
sleep aids out there.

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

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And it can be problematic for your sleep

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in at least three different ways.

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First, alcohol is in a class of drugs

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that we call the sedatives.

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But sedation is not sleep.

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And studies teach us that those two things

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are really quite different.

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Sedation is a case

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where we're simply
switching off the firing

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of the brain cells,
particularly in the cortex.

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And that's not natural sleep.

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

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for example, the brain has
this remarkable coordination

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of hundreds of thousands of cells

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that all of a sudden fire together,

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and then they all go silent,

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

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producing these big, powerful brainwaves

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of deep non-REM sleep.

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And so that's the first way

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in which alcohol can be problematic.

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We're mistaking sedation for deep sleep.

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The second problem with alcohol

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is that it can actually
fragment your sleep.

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Alcohol can actually trigger
and activate during sleep

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what we call the fight or flight branch

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of the nervous system,

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which will therefore
wake you up more frequently

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throughout the night.

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And alcohol can even increase the amount

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of alerting chemicals
that are released by the brain,

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once again fragmenting your sleep.

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The third and final issue
with alcohol and sleep

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is that alcohol can actually block

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your rapid eye movement sleep,
or your dream sleep.

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And as we'll learn in subsequent episodes,

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

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provides a collection of benefits,

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things such as your emotional

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and mental health, even creativity.

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

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I don't want to be puritanical.

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I'm just a scientist.

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What I want to try and do is provide you

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with the information
about the relationship

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between caffeine and alcohol on your sleep

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so then you can make an informed choice

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as to how best you want to live your life

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when you're trying to
prioritize your sleep health.