Matt Walker
1,490,789 views • 4:54

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.