Science & Tech
The Buzz on Alcohol and Caffeine
Lesson time 17:36 min
Matthew explains how these two substances affect your sleep and offers tips on how to manage your sleep if you choose to imbibe.
[MUSIC PLAYING] - Alcohol and caffeine can impact our sleep in some surprising ways. Let's take caffeine to begin with. Caffeine is a stimulant, and we all know that caffeine alerts us and makes us feel more awake. It's in a class of drugs that we actually call the psychoactive stimulants. But even though we all know that caffeine wakes us up and makes us more alert, there are at least two other features of caffeine that you may be less familiar with. The first of those is the timing of caffeine and specifically its duration of action. Caffeine has a half-life of about five to six hours for the average adult. What that means is that about 50% of that caffeine is still circulating in your system five to six hours after you had that cup of coffee. What that also means, however, is that caffeine has a quarter-life of somewhere between 10 to 12 hours. So in other words, if you have a cup of coffee at let's say 2:00 PM in the afternoon, a quarter of that caffeine can still be circulating in your brain at midnight. So having a cup of coffee in the afternoon may be the equivalent of tucking yourself into bed at midnight, and just before you do, you swig a quarter of a cup of coffee and you hope for a good night of sleep. And that's unlikely to happen for some of us. The second hidden feature of caffeine is it's disruption in terms of our sleep quality. Now, some people will tell me, look, I'm one of those individuals I can have an espresso with dinner, and I fall asleep just fine. And I stay asleep. I don't have a problem with caffeine. But even if that's true, it turns out that caffeine can decrease the amount of deep sleep that you have, stages three and four of non-REM sleep. And so as a consequence, you wake up the next morning and you don't feel as restored by your sleep. You don't feel refreshed. But you don't remember struggling to fall asleep. And you don't remember waking up at night. So you don't connect the dots. You don't connect the two. But, now, you find yourself reaching for maybe two or three cups of coffee the next morning to feel wide awake because of what we call unrestorative sleep. I should note, by the way, that there's a huge amount of variability in our sensitivity to caffeine. And in fact, we know why. Because there are specific enzymes that are determined by specific genes that we know of, which will speed up or slow down the metabolism of caffeine. And that's why some people will say I am very sensitive to caffeine. I just need one cup of caffeine in the morning, and that's me. Otherwise, I get the jitters, and it's too much. Other people can drink caffeine maybe up to midday, and they're just fine. The way in which caffeine works comes back to something we've spoken about previously, which is adenosine and sleep pressure. And so we mentioned that adenosine builds throughout the day. And the more that we're awake, the more adenosine builds up, and the sleepier that we feel. Now, you may...
About the Instructor
As a professor of neuroscience and psychology at UC Berkeley and the director of the Center for Human Sleep Science, Matthew Walker is an expert on sleep. In this class, he will illuminate the science behind sleep and teach you how to increase the quality and quantity of your sleep. Learn how to prevent sleep debt, navigate the effects of alcohol and caffeine, and improve your health. Your best sleep starts tonight.