Sleep science: discussing cause and effect

B2
60 min
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1

Think about these questions before watching. Share your ideas with a partner.

  1. Describe your typical daily routine when it comes to drinks like coffee, tea, or energy drinks. How do you think these habits affect your productivity and mood?
  2. Think about the last time you had a really poor night's sleep. What factors do you believe contributed to it, and how did it impact your following day?
  3. What are some popular beliefs in your culture about how certain foods or drinks can affect sleep or energy? Do you personally agree or disagree with them based on your experience?
2

Watch the video carefully. Pay attention to the main ideas and key details.

Video script105 segments · click a timestamp to jump

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.

3

Answer these questions in your own words. Support your answers with evidence from the video.

01According to the video, how can a cup of coffee consumed in the afternoon affect your sleep later that night?
Sample answerThe video explains that caffeine has a long 'half-life' of about five or six hours. This means if you have coffee at 2 PM, a quarter of the caffeine could still be in your brain at midnight, making it difficult to fall asleep properly.
02Why might someone who drinks coffee in the evening believe it doesn't affect their sleep, even when it actually does?
Sample answerThey might think it's fine because they can still fall asleep and stay asleep without waking up. However, the video says caffeine reduces the amount of deep, restorative sleep. So, they wake up feeling tired without realizing why and don't connect it to the coffee they had.
03In what way is the sedation caused by alcohol different from natural deep sleep?
Sample answerThe speaker explains that sedation from alcohol just switches off the brain's cells. Natural deep sleep is very different because it involves hundreds of thousands of brain cells firing together and then going silent in a coordinated way, creating powerful brainwaves.
04What are the three main problems with alcohol that the video identifies as being harmful to sleep?
Sample answerFirst, it causes sedation, which isn't the same as natural sleep. Second, it fragments your sleep by waking you up more often. And third, it can block your REM or dream sleep, which is important for emotional health.
4

Vocabulary

Vocabulary
These expressions will help you communicate more naturally about this topic.
Examples
To be wired — to be unusually energetic, alert, or tense, often from consuming a stimulant like caffeine.
Usage note: This is an informal idiom. You can say 'I'm feeling really wired' or 'That coffee has me completely wired'.
To wear off — for the effects of something (like medicine, a drink, or a feeling) to gradually decrease and disappear.
Usage note: This is a common phrasal verb. For example, 'I need another coffee; the effects of the first one are starting to wear off'.
To toss and turn — to move around restlessly in bed because you are unable to sleep.
Usage note: This idiom vividly describes a difficult night. You might say, 'I was tossing and turning all night and feel exhausted today'.
A light sleeper — a person who is easily woken up by noise or other disturbances.
Usage note: The opposite is 'a heavy sleeper'. This is a useful collocation to describe your sleep habits, e.g., 'My partner is such a light sleeper that I have to be silent in the morning'.
To knock someone out — to cause someone to fall asleep very quickly and deeply.
Usage note: This is informal and often refers to the strong effect of medicine or alcohol. It implies an unnatural, heavy sleep, which connects to the video's point about alcohol. Example: 'One glass of wine is enough to knock me out'.
5

Decide if each statement is true or false. Correct the false ones.

01According to the video, a cup of coffee you drink in the early afternoon can still be affecting you at midnight.
02Alcohol can interfere with dream sleep, also known as REM sleep, which is important for mental health.
03The video states that caffeine is a sedative drug that helps people relax.
04Even if you can fall asleep easily after drinking coffee, it can still reduce the amount of deep, restorative sleep you get.
05Alcohol fragments sleep because it calms the nervous system completely throughout the night.
6

Discuss these questions with a partner. Try to use vocabulary from the lesson.

  1. In many cultures, business meetings or social gatherings in the afternoon or evening involve coffee. After watching the video, do you think this is a problematic tradition? Discuss the social benefits versus the potential impact on sleep, especially considering how long it takes for caffeine's effects to wear off.
  2. Some people argue that adults should be responsible for their own caffeine intake, while others believe companies and cafes should do more to warn customers about the risks of late-day consumption. What is your stance? Is this a matter of personal choice or corporate responsibility?
  3. The video explains that even if you fall asleep easily after drinking caffeine, it can reduce your deep sleep. How might this information change your own habits, especially if you are a light sleeper or find yourself tossing and turning at night?