Caffeine: How Much Is Too Much?

Today we’re revisiting caffeine. It’s a drug that tons of us take every day. So, is that a bad thing?? What is it really doing to our bodies and our brains? Plus — if we get it in the form of energy drinks, is that super dangerous? We talk to Dr. Astrid Nehlig, Prof. Gregory Marcus, and Prof. Sachin Shah. [REBROADCAST] Find our transcript here: https://tinyurl.com/ScienceVsCaffeine In this episode, we cover: (00:00) Our love/hate relationship with caffeine (04:40) How coffee affects our gut (07:29) How coffee affects our brain (12:59) How coffee affects our sleep (17:58) Coffee makes us go vroom vroom vroom! (20:45) Are we caffeine addicts?? (28:15) Are energy drinks dangerous? This episode was produced by Rose Rimler, with help from Wendy Zukerman, as well as Nick DelRose, Joel Werner, and Michelle Dang. We’re edited by Blythe Terrell. Fact checking by Sarah Baum. Mix and sound design by Bumi Hidaka. Music written by Bobby Lord, Bumi Hidaka, Emma Munger and Peter Leonard. Special thanks to all the researchers we spoke to for this episode – including Dr. Bryan Saunders, Dr. Sergi Ferré, Prof. Andreas Heinz, Prof. Christine Curran, Dr. Erikka Loftfield, Dr. Felix Oberhoffer, Dr. Alan Wayne Jones, and Dr. Vijay Yadav. Extra special thanks to Jason Vytlacil and the Zukerman family. Science Vs is a Spotify Studios Original. Listen for free on Spotify or wherever you get your podcasts. Follow us and tap the bell for episode notifications. Learn more about your ad choices. Visit podcastchoices.com/adchoices

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Wendy Zukerman?

  Hi, I'm Wendy Zukerman and you're listening to Science Versus. And this is the show that pits facts against flat whites.

• 0:08Wendy Zukerman?

  On today's show, caffeine, should you quit it?

• 0:17Wendy Zukerman?

  Caffeine is one of the most used drugs in the world. Eighty-five percent of people in the US drink at least one caffeinated beverage each day, and that includes kids. But yet, despite the fact that we are shoving this drink down our pie holes, there have always been these fears that caffeine is bad for our health.

• 0:38Speaker 01

  Your cup of coffee could soon come with a spoonful of cancer warning.

• 0:41Speaker 02

  My heart was racing, I was super anxious, something was happening, I was having a panic attack. Could it all be a sign, though, of a serious problem? A problem like caffeine addiction.

• 0:50Wendy Zukerman?

  And our worries around caffeine have reached new heights when it comes to energy drinks. Just last year, a 17-year-old from Texas died after drinking Alani New.

• 1:00Speaker 03

  A Texas family is filing a wrongful death lawsuit over an energy drink that they claimed killed a teenage girl.

• 1:07Speaker 04

  According to family lawyers, a coroner's report shows that she died from an enlarged heart caused by stress and a large amount of caffeine from Alani Energy Drinks.

• 1:17Wendy Zukerman?

  The distributor being sued denies the claims, and the company that makes the drink says it's labeled "not recommended for children." But this is just the latest in a string of scary stories from the past several years of people, often younger people, dying soon after drinking energy drinks.

• 1:35Speaker 05

  Davis collapsed in the classroom of his high school in South Carolina.

• 1:38Speaker 06

  It wasn't a car crash that took his life. Instead, it was an energy drink. She drank two 24-ounce energy drinks in less than 24 hours. And it took her life.

• 1:54Wendy Zukerman?

  So today on the show, what is this drug doing to our brains and our bodies? Is it ruining our sleep, turning us into caffeine addicts, and potentially even killing us? When it comes to caffeine, there's a lot of...

• 2:07Speaker 02

  My heart was racing.

• 2:08Wendy Zukerman?

  But then, there's science.

• 2:12Wendy Zukerman?

  Science versus caffeine is coming up just after the break.

• 2:22Speaker 07

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• 3:06Speaker 07

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• 3:28Wendy Zukerman?

  Welcome back. Today on the show, we're taking on caffeine and energy drinks to find out, once and for all, how bad is this stuff? What is it doing in our bodies and our brains? And we first drank up the science on caffeine a few years ago when we first put down this episode. And back then, there was all of this hubbub about the energy drink prime. And that's what got senior producer Rose Rimler interested in this topic in the first place.

• 3:55Speaker 04

  Yeah. A lot of the talk was about how it's got a crazy amount of caffeine. It's bad for us. And energy drinks are bad for us. And sort of just this feeling that caffeine is bad for us. And I don't know about you, but I have caffeine every day when I have my coffee. So it made me wonder, like, is my caffeine habit something I should take a second look at? Or is caffeine just all hunky-dory?

• 4:19Wendy Zukerman?

  Yes. I love this question because caffeine has been a thing that I have actively said, you know what? I'm not into meth, but I'm gonna be fine with my caffeine use. You know, I felt guilty about it. And I do want to know whether I need to. So where do we begin?

• 4:37Speaker 04

  Let's start with Astrid Nehlig. She's a caffeine researcher. And she says she hears this idea about people feeling guilty about their caffeine intake all the time.

• 4:47Speaker 02

  I meet somebody and they ask me on what I work. And I say, I work on coffees. And people are very shy all of a sudden and withdrawing a bit and telling me, oh, it's very bad. I should probably not drink.

• 5:04Speaker 04

  Astrid is an emeritus research director at France's National Institute of Health and Medical Research, and she has studied caffeine for decades. So with her help, I'm going to walk you through what caffeine is doing to your brain and to your body.

• 5:21Wendy Zukerman?

  Okay.

• 5:22Speaker 04

  So Wendy, I asked you to come prepared with your favorite caffeinated beverage.

• 5:26Wendy Zukerman?

  That's right.

• 5:27Speaker 04

  So what did you bring today?

• 5:28Wendy Zukerman?

  I have an oat cappuccino.

• 5:30Speaker 04

  Okay, take a sip.

• 5:31Wendy Zukerman?

  Should I do it like ASMR? Or if I'm, I guess if you have misophagia, just chewed out.

• 5:35Speaker 04

  Okay, so I'm going to tell you what it's doing right now.

• 5:40Wendy Zukerman?

  Okay.

• 5:41Speaker 04

  So scientists think that once the coffee gets to your stomach, it's basically going to wake up your guts. It's going to get your stomach to make more acid. It's going to get your liver to start making bile.

• 5:53Speaker 02

  So it's really an activator of digestion.

• 5:57Speaker 04

  Is that why, not to be crude, but sometimes you have to go number two after you drink coffee?

• 6:04Speaker 02

  Yeah, at least in some especially sensitive individuals, yeah, it's like that.

• 6:10Speaker 04

  We know this because thankfully, some scientists in the 80s got permission to stick probes up people's buttholes.

• 6:18Wendy Zukerman?

  Oh.

• 6:19Speaker 04

  And then give them coffee to see what happens. And the reason they wanted to test it this way is because they had given these people a survey and said, does, do any beverages make you have to poop? And a third of the people in this 100-person survey said, yeah, actually, coffee.

• 6:35Wendy Zukerman?

  Yeah.

• 6:36Speaker 04

  Makes me have to poop. So they got some of these people and some other, you know, non-responders into the lab, and they put this probe up, up in their, up their part of their rectum. And so what they were looking for was to see, is there an actual physical change in your lower intestine when you've had coffee?

• 6:55Wendy Zukerman?

  And what did they find?

• 6:56Speaker 04

  In the people who said, yes, coffee does this to me, they could actually measure increased rectal activity.

• 7:04Wendy Zukerman?

  Oh.

• 7:04Speaker 04

  So that-

• 7:05Wendy Zukerman?

  I'm clenching. I'm clenching. Have you been clenching as you've been reading this research?

• 7:09Speaker 04

  No, I'm quite relaxed.

• 7:10Wendy Zukerman?

  Oh, okay. As soon as you said increased rectal activity, I was just like...

• 7:16Speaker 04

  Well, I like thinking about these sort of peristalsis of your butthole.

• 7:20Wendy Zukerman?

  Yeah, it's graceful.

• 7:22Speaker 04

  How food gets down. Something else has to make it come out. And that increased-

• 7:27Wendy Zukerman?

  Right.

• 7:28Speaker 04

  -in response to coffee for some people.

• 7:30Wendy Zukerman?

  Interesting. Okay, I have a very important question.

• 7:33Speaker 04

  Yeah.

• 7:34Wendy Zukerman?

  How quickly? How quickly does this activation happen? Because-

• 7:40Speaker 04

  It can happen within minutes.

• 7:42Wendy Zukerman?

  Oh, my God, I feel so validated. Wow. Because I, like, I will sometimes just take a few sips of coffee and just like, need to do a [BLEEP]. Sorry for the kids out there. Need to do a big crap. And I have come to believe that, oh, it's just placebo at this point. Like, surely it can't be working that quickly, but it can.

• 8:05Speaker 04

  It can.

• 8:06Wendy Zukerman?

  Like, just so you know, Rose, because this is my first coffee for the day.

• 8:10Speaker 04

  Yeah, if you have to run off on the way.

• 8:13Wendy Zukerman?

  No, I don't. Because I took a couple of sips before our chat. And I'm also-

• 8:18Speaker 04

  Took care of business?

• 8:24Speaker 04

  I appreciate that level of planning. Always come prepared.

• 8:27Wendy Zukerman?

  That is me.

• 8:29Speaker 04

  Okay. So that's how coffee can affect the gut. And from there, caffeine starts getting absorbed in your bloodstream.

• 8:36Wendy Zukerman?

  Okay.

• 8:36Speaker 04

  Depends on your body, but this takes about half an hour to an hour to peak. So caffeine's in your blood. It gets to the blood-brain barrier, and it just sails right past it. I talked to Astrid about this. When I think of coffee entering our brain-

• 8:51Wendy Zukerman?

  Yes.

• 8:52Speaker 04

  I just imagine my brain is a sponge that just soaks up the coffee. Is that kind of right?

• 8:59Wendy Zukerman?

  Yeah, why not? Yes, because, you know, you drink your coffee, and all of a sudden, your whole body, including your brain, gets invaded by this caffeine.

• 9:10Speaker 04

  In the brain, it stimulates some neurotransmitters, including dopamine, and that gives us a bit of a mood boost. But the big thing that caffeine does in our brain is, of course, that it wakes you up.

• 9:22Wendy Zukerman?

  Yes.

• 9:23Speaker 04

  Yes, it's claim to fame. And this happens because caffeine basically barges into the brain and like elbows out this molecule called adenosine from these special receptors.

• 9:35Wendy Zukerman?

  Mm hmm.

• 9:36Speaker 04

  And what adenosine is, it's like the sleepy molecule. So it like binds receptors in your brain that basically turn on the feeling of sleepiness. So caffeine's like, out of my way, I'm coming in. I'm gonna bind to those adenosine receptors. And that means you don't feel sleepy.

• 9:54Wendy Zukerman?

  So just to get like real nerdy here, it's not that caffeine is binding onto these receptors and going, let's go, brain, get excited. It's rather the lack of adenosine, the lack of sleepiness that wakes you up.

• 10:11Speaker 04

  Yeah, and that's what we like about caffeine, right? Like, that is the whole point, that it wakes us up. And it's not just about being awake. We actually have a lot of evidence that caffeine helps us be more alert, more focused, and helps us to react to stuff faster.

• 10:26Wendy Zukerman?

  This has been quite extensively studied, this is clear. So for, if I take a stupid example, but

• 10:34Speaker 04

  Please.

• 10:34Wendy Zukerman?

  You, you are facing a lion. If you have been drinking caffeine, you will react faster and you will run away before.

• 10:46Speaker 04

  Could save your life.

• 10:47Wendy Zukerman?

  Yes, could, absolutely. Could make a difference and save your life.

• 10:51Speaker 04

  And scientists have actually tested this. They gave free coffee to people who were visiting the zoo that day, and then they opened the lion cage.

• 11:01Wendy Zukerman?

  Amazing, and they got away, they got away.

• 11:03Speaker 04

  Some got away, some didn't.

• 11:05Wendy Zukerman?

  That's right, those in the placebo group were less likely to get away. We are joking.

• 11:10Speaker 04

  No, there are no lines. But there is one small study that suggests that caffeine really could save your life. So this study, researchers had people stay up really late and then drive a car on the highway in the middle of the night. This is a real car and a real highway.

• 11:26Wendy Zukerman?

  Oh, my god.

• 11:27Speaker 04

  They had a driving instructor in the next seat who could take over control if things were getting bad.

• 11:32Wendy Zukerman?

  My goodness.

• 11:33Speaker 04

  So the scientists were counting how many times people veered out of their lane when they had placebo versus when they had coffee. And it turns out the coffee made a big difference. The number of times people veered over the lane went way down after people had coffee.

• 11:48Wendy Zukerman?

  Okay, the palace of caffeine.

• 11:51Speaker 04

  Yes, right. And then I found this study that just made me laugh because it's just such a funny concept. The scientists really wanted to find out if coffee can make us appreciate humor more. When we are sleep deprived, we kind of lose our sense of humor, or it takes a hit. So the researchers were wondering, would caffeine give us back our sense of humor or improve that?

• 12:14Wendy Zukerman?

  Uh huh.

• 12:15Speaker 04

  And I don't know if you know this, Wendy, but there is a scientific test of sense of humor.

• 12:21Wendy Zukerman?

  Oh, my gosh, that was entirely my next question. What is the joke that scientists ask that they're like, if you find this funny, you have a good sense of humor?

• 12:31Speaker 04

  Then you're operating on full cylinders. Yeah, so they would show them like two different pictures and ask which picture is funnier, or more podcast appropriate, they would have them read two different headlines, fake news headlines, and ask which is funnier. So here's an example. I'm curious if you're gonna get it right.

• 12:47Wendy Zukerman?

  I feel very cocky about my sense of humor.

• 12:50Speaker 04

  Okay, so here's the example. Which of these two headlines is funnier? Veterinarian investigates fails panda mating. That's headline one. Or panda mating fails, veterinarian takes over. That's headline two. Which is funnier?

• 13:07Wendy Zukerman?

  Headline two is funnier because it suggests. I mean, headline one isn't funny at all, right? But headline two suggests.

• 13:15Speaker 04

  Just something really, really disturbing, actually.

• 13:20Speaker 04

  And the third headline is veterinarian f***ing panda.

• 13:27Speaker 04

  You're right, it is the second headline.

• 13:30Wendy Zukerman?

  Yes.

• 13:31Speaker 04

  According to science, that is objectively funnier, which I guess it is.

• 13:34Wendy Zukerman?

  Also, I'm so proud of them for being a bit naughty.

• 13:38Speaker 04

  Well, it turns out that the caffeine in this case did not help people.

• 13:41Wendy Zukerman?

  Yeah, I totally forgot we were talking about caffeine.

• 13:47Speaker 04

  So, bottom line, caffeine may not improve your humor, but we have lots of evidence to show that it's not a myth or a placebo effect. Like caffeine does help us wake up, stay up, stay alert. So that brings us to something that people actually worry about with caffeine, that it's keeping you too awake, that it's messing with your sleep.

• 14:09Wendy Zukerman?

  Yes, I have worried about this too. And in fact, cut down on caffeine because I've been worried about this.

• 14:14Speaker 04

  So let's meet Gregory Marcus.

• 14:16Speaker 03

  I'm just gonna move my dog. Come on.

• 14:19Speaker 04

  He's a cardiologist and a professor of medicine at UCSF. If you could be any caffeinated product, which caffeinated product would you be?

• 14:28Speaker 03

  Oh, cappuccino, no doubt.

• 14:30Wendy Zukerman?

  I guess he sees himself as serious on the bottom, but like a little bit frothy and sweet on the top.

• 14:35Speaker 04

  You know, he didn't refer to himself that way, but based on my conversation with Greg, I would say that's an accurate description of him.

• 14:43Speaker 03

  Buttercup has been removed for the moment.

• 14:49Speaker 04

  So Greg did this like pretty unique study where he got people to either drink coffee or not drink coffee at random. And then he was able to like precisely measure exactly how that affected their sleep.

• 15:02Wendy Zukerman?

  Ooh, okay.

• 15:04Speaker 04

  So they recruited about 100 coffee drinkers in San Francisco. They put a bunch of stuff on them. They wore a Fitbit, which measured how well they slept and their steps. And they wore a portable heart monitor. So it's essentially like a very big Band-Aid. And it goes on the chest to the left of the sternum, essentially. And like, interestingly, in the middle of the sticker, there's this big button. We instructed them, just push that button whenever you have a cup of coffee or a caffeinated drink. So you have your coffee and you hit your button.

• 15:39Speaker 04

  And one way they made sure that people were doing what they were supposed to do, you know, not drinking coffee if they weren't supposed to that day.

• 15:46Wendy Zukerman?

  Uh huh.

• 15:46Speaker 04

  They had everyone in the study get this app on their phone that allowed the team to monitor their location. So the team could see if they visited coffee shops. So if they went to a coffee shop on a day they weren't supposed to have caffeine, that would be highly suspicious. Would they get like, would there be like a button goes off in your office? Like a flashing red light, where they get an electric shock? Yeah, that's a good idea, interesting idea.

• 16:15Wendy Zukerman?

  That's exactly what I was thinking.

• 16:17Speaker 04

  Well, luckily for the people in the study, we didn't design it.

• 16:21Wendy Zukerman?

  No.

• 16:21Speaker 04

  We did not get shocked.

• 16:22Wendy Zukerman?

  Oh, okay, okay. So I'm gonna, I'm gonna go out on a limb here, Rose, and say that on average, coffee did affect people's sleep.

• 16:32Speaker 04

  Yes, but the key question here is how much? Because there is this idea that coffee just really robs you of your sleep. Well, in reality, Greg found. On days where people were randomly assigned to consume coffee, that evening, they, on average, slept 30 minutes less.

• 16:52Wendy Zukerman?

  Ah!

• 16:53Speaker 04

  Yeah, so on average, if they were in the coffee drinking group, they had half an hour less sleep. And Greg could even dive into the research and figure out how much sleep each cup of coffee cost these people. And it turns out about 15 minutes of sleep.

• 17:09Wendy Zukerman?

  Okay, so loosely for every shot of espresso or just like regular coffee. You'll get around 15 minutes less sleep a day. Uh huh, okay.

• 17:19Speaker 04

  Yes, but-

• 17:20Wendy Zukerman?

  That's not, oh, oh, uh, but-

• 17:23Speaker 04

  There is an important caveat, which is that Greg found this really varied from person to person based on their genetics. So on top of all that other stuff, Greg also took saliva samples from people and worked out if they had these genes that make them either a fast or a slow metabolizer of caffeine. And he found that the slow metabolizers lost closer to an hour of sleep a night, on average. And the fast metabolizers lost basically no sleep at all.

• 17:54Wendy Zukerman?

  Huh.

• 17:55Speaker 05

  So people who say, "Oh yeah, I can have a, you know, cup, cup of coffee at night, I go right to sleep," they may be really telling the truth.

• 18:03Wendy Zukerman?

  My mom proudly says that she can drink coffee, like, at dinnertime, and it will not affect her sleep, to the point where she will mock me when she wants a coffee at 4:00 PM and I say, "Too late for me." Mama Zook vindicated once more by a Science vs. episode.

• 18:19Speaker 04

  Well, it's like you're both right. She's right that she can have a coffee late at night, and you're right that you can't. You're probably both right.

• 18:27Wendy Zukerman?

  Okay. But you know who isn't right? Is those people online, influencers, I don't know what we want to call them, anyway, who have these like definitive statements about how much coffee you're allowed to drink and you need to stop at 10:00 AM and you can only drink two cups or whatever, whatever that they're saying, like, actually what the science says is this is very dependent on your genetics. And, and, and those blanket statements are kind of bollocks.

• 18:56Speaker 04

  Yeah. Okay, so that's sleep. But Greg's study looked at something else that people don't necessarily associate with having a cup of coffee, and that is exercise. So on top of measuring sleep, he also measured how many steps they took every day. And-

• 19:15Speaker 05

  On days randomly assigned to coffee, participated- On average exhibited a thousand more steps on those days.

• 19:24Speaker 04

  Wow, that's a lot.

• 19:25Speaker 05

  It is a lot. And in fact, there's other evidence that that magnitude of a difference may be meaningful in the long run in enhancing longevity.

• 19:37Wendy Zukerman?

  Oh, wow.

• 19:38Speaker 04

  Yeah. For example, one study found that older women who take 5,000 steps a day live longer than similar women who took 4,000 steps a day.

• 19:46Wendy Zukerman?

  Oh, that's cool.

• 19:48Speaker 04

  And it's not just step count. We actually have a lot of data showing that caffeine can help us athletically. So when people have caffeine before they exercise, they tend to go a little harder. So like people will be able to run for longer or, for example, do more squats.

• 20:05Wendy Zukerman?

  Cool.

• 20:06Speaker 04

  There's a study that looked at swimmers doing a 1,500 meter race. So that's almost a mile. And it found that having some caffeine beforehand shaved 23 seconds off their time compared to a placebo. And having caffeine before exercise is considered safe as long as you don't overdo it. Like it's the equivalent of one or two coffees before exercising.

• 20:29Wendy Zukerman?

  Wow.

• 20:32Wendy Zukerman?

  And so why is that happening?

• 20:34Speaker 04

  Well, you know how caffeine can boost your dopamine? So that might be like putting us in a better mood so we can work harder. And we also know that caffeine can kind of turn the dial down on feelings of pain. That's why some painkillers have caffeine in them. So maybe athletes aren't feeling the burn quite as much. And then finally, there's some evidence that caffeine can actually increase the amount of calcium getting released by your cells, which could make your muscles work better.

• 21:03Wendy Zukerman?

  Wow.

• 21:04Speaker 04

  So Wendy, do you still feel guilty about your coffee?

• 21:09Wendy Zukerman?

  Oh, no.

• 21:13Wendy Zukerman?

  Thus far, no. But at the same time, we haven't really talked about risks yet.

• 21:19Speaker 04

  Good point. So next, we're going to talk about is caffeine addictive? And what's going on with the scary stories we hear about people dying after drinking energy drinks?

• 21:30Wendy Zukerman?

  And that's coming up just after this quick coffee break.

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• 22:17Wendy Zukerman?

  Welcome back. Today on the show, we are asking, should you quit your caffeine? Should you spit out your coffee? Spill your tea on the floor? Say goodbye to your energy drinks? Rose Rimmler, senior producer at Science Versus, is telling us all about it. Hey, Rose.

• 22:33Speaker 04

  Hey, Wendy. So the next thing I want to dive into is this idea that you can get addicted to caffeine. You know, and I think a lot of that comes from this, like, terrible withdrawal that some people have when they stop it. Now, caffeine withdrawal is a real thing. And people who quit coffee, all of a sudden, can totally feel sick. Like, about half of them will get a headache. This could be because caffeine restricts blood flow to the brain. And when they go off it, the blood whooshes back in.

• 23:02Wendy Zukerman?

  Oh, wow.

• 23:03Speaker 04

  Some people even feel like they have the flu and they feel like really tired and crappy. So send them help. So pray for them.

• 23:09Wendy Zukerman?

  Do I need to pray for them? Do I? Like, if they, if suddenly there was an apocalypse and they couldn't get their coffee, how bad would it be?

• 23:15Speaker 04

  All those symptoms, they go away for most people somewhere between two to nine days.

• 23:21Wendy Zukerman?

  Okay, so if they can survive for nine days, they'll be back to normal.

• 23:25Speaker 04

  Yes, just hunker down in your bunker. Hunker in your bunker.

• 23:28Wendy Zukerman?

  Great.

• 23:29Speaker 04

  And it'll play itself out.

• 23:31Wendy Zukerman?

  Right, okay.

• 23:32Speaker 04

  But back to this addiction thing. So, you know, you might reasonably call yourself dependent on caffeine if you feel sick without it. But that's not the same thing as addiction. With addiction, what experts point to is that you are using a substance even though it's bad for you, has negative consequences on your life, maybe you even like really want to quit and you can't. And I think right now, the general idea among scientists is that this is not a problem for most people. They don't really see it, any evidence of this like negatively affecting people.

• 24:06Wendy Zukerman?

  Right, for most people. And then what about tolerance? Like this idea that you need to have more and more caffeine to have the same effect?

• 24:14Speaker 04

  Yeah, we typically don't really see that with caffeine. And one reason is probably that at a high dose, caffeine starts to activate this other type of adenosine receptor in our brain that causes anxiety.

• 24:29Wendy Zukerman?

  Oh, this is why you get all like jittery and like, ooh, if you have too much caffeine.

• 24:35Speaker 04

  There's sort of a threshold you can cross from all the feeling like alert and energetic and kind of good to, oh, now I feel anxious and jittery and weird. And one researcher I spoke to said that for caffeine specifically, this window, this, he calls it a window between the good and the bad feelings, is pretty short. So you can kind of easily tip yourself over when you've had more caffeine into that anxious feeling. And if you're starting to feel that way, you know, many people would probably put down their third venti frappuccino of the day, you know, at that point.

• 25:08Wendy Zukerman?

  Yes.

• 25:09Speaker 04

  So there's kind of a natural cap for most people on how much caffeine we're going to drink every day.

• 25:14Wendy Zukerman?

  Yeah, yeah, yeah, yeah. You know, because recently I did, I was like, fuck it, I'm just going to drink more coffee. And it did make me feel anxious. And so I was like, no, no, just go back to one or two cups. Like just, yeah, this isn't, go for a run instead or whatever.

• 25:29Speaker 04

  Yeah, it's not like worth it to most people.

• 25:33Wendy Zukerman?

  Yeah.

• 25:34Speaker 04

  At a certain point. And you know, this can be different if you're mixing caffeine with other drugs, that's more dangerous. But bottom line, caffeine is not considered a drug of abuse. There is no caffeine use disorder in the DSM, you know, the big manual for psychiatric disorders. It's been proposed, but right now it's not officially in there.

• 25:56Wendy Zukerman?

  Okay, so. So for now, we could say sci- science says caffeine isn't really that addictive. Is that where we're at?

• 26:04Speaker 04

  I think so. I think, yeah. Yeah, I think so.

• 26:08Wendy Zukerman?

  So thus far, all right, it doesn't. It's really not seeming like caffeine is that bad. And I'm trying to think why I thought caffeine was bad for you.

• 26:19Speaker 04

  I actually might have an answer.

• 26:22Speaker 04

  In the 90s, there was news that coffee was associated with bladder cancer.

• 26:28Wendy Zukerman?

  Oh, really?

• 26:29Speaker 04

  But that has been debunked in more recent years.

• 26:32Wendy Zukerman?

  Okay.

• 26:33Speaker 04

  Turns out it was not a real association. But even if you don't remember that stuff about bladder cancer, I think that sort of percolated, so to speak, in the culture.

• 26:42Wendy Zukerman?

  Mm-hmm.

• 26:43Speaker 04

  And we haven't quite gotten over it.

• 26:44Wendy Zukerman?

  Uh-huh, okay.

• 26:45Speaker 04

  Plus, there's a lot of fears around pregnancy and caffeine.

• 26:49Wendy Zukerman?

  Right.

• 26:50Speaker 04

  And that is something to think about because we know that caffeine can cross the placenta and get to the fetus. And so drinking a lot of caffeine when you're pregnant isn't recommended.

• 26:59Wendy Zukerman?

  Mm-hmm.

• 27:00Speaker 04

  But, you know, health guidelines from around the world, they say you can have one or two cups of coffee a day if you're pregnant.

• 27:05Wendy Zukerman?

  Right, right.

• 27:05Speaker 04

  You know, overall, just putting aside pregnancy, I walked away feeling pretty reassured about caffeine. Because here's something that I thought was like really kind of great. So it turns out that people who drink coffee have a lower risk of Parkinson's disease, depression, type 2 diabetes, and heart disease.

• 27:27Wendy Zukerman?

  Really?

• 27:28Speaker 04

  And although we once thought coffee was carcinogenic, more recent studies have found that it actually might reduce your risk of some cancers.

• 27:35Wendy Zukerman?

  What?

• 27:36Speaker 04

  Like liver and breast cancer.

• 27:37Wendy Zukerman?

  Are you kidding me? Are you s- like?

• 27:40Speaker 04

  Yeah, and even drinking coffee is associated with being less likely to die earlier. So the biggest benefits are seen in people who drink two to three cups a day. But even at higher amounts, we still people apparently getting some benefit. Like, one study looked at people drinking as much as eight cups of coffee a day.

• 27:59Wendy Zukerman?

  What?

• 28:00Speaker 04

  And found they still lived a little longer than people who didn't drink any coffee.

• 28:03Wendy Zukerman?

  Wow.

• 28:04Speaker 04

  Yeah, I mean, there aren't that many people that drink eight cups of coffee a day, so that's kind of a smaller sample size. But I think that point stands that the science suggests that coffee is not actively harming you. And caffeinated tea also seems to be good for us.

• 28:18Wendy Zukerman?

  I mean, are we sure? Are we sure about this? Like, why would caffeine, why would coffee and tea have these benefits?

• 28:25Speaker 04

  I mean, nobody totally knows. It could have something to do with the exercise boosts you get from caffeine. Because like we said earlier, like, walking more steps a day. But also, it could be that it's not really about the caffeine. It's about the other stuff that's in the plant. So the coffee bean, the tea leaf. There's a lot of stuff in there that's really good for us and is anti-inflammatory and has antioxidant potential.

• 28:50Wendy Zukerman?

  Wow, I'm feeling very good about my coffee use. I was not expecting this from science, but thank you.

• 28:57Speaker 04

  Anytime.

• 28:58Wendy Zukerman?

  So then, what, I don't want to crap all over this party. Is that how that phrase goes?

• 29:06Speaker 04

  Yes.

• 29:10Wendy Zukerman?

  Rain on your parade?

• 29:11Speaker 04

  Yes, yes.

• 29:16Speaker 04

  That's a very, it's a visceral expression.

• 29:23Wendy Zukerman?

  I don't know if I have a good sense of humor. I just laugh so much at my own jokes.

• 29:27Speaker 04

  I know a test you can take.

• 29:29Wendy Zukerman?

  Great. Okay, but, but, but, but, what does this all mean about the energy drinks issue? Because to change the tune, to get quite serious, like, there are these stories about energy drinks killing people. So what does this mean?

• 29:50Speaker 04

  Which is the opposite of what I just told you about coffee, right?

• 29:54Wendy Zukerman?

  Yeah.

• 29:55Speaker 04

  Well, a lot of times what people say is the problem is that energy drinks are dangerous because they are packed way too full of caffeine.

• 30:03Wendy Zukerman?

  Right, right.

• 30:04Speaker 04

  But the funny thing is, when you look at the labels, many of them really don't have that much caffeine in them.

• 30:10Wendy Zukerman?

  Oh, how much caffeine is in your average energy drink?

• 30:13Speaker 04

  Well, okay, so like Chuck Schumer said that Prime Energy had an eye-popping amount of caffeine. So I looked up the label of Prime. It contains 200 milligrams of caffeine.

• 30:24Wendy Zukerman?

  What? 200? What, like two, two shots of espresso? That's it? That's it?

• 30:30Speaker 04

  Yeah, two, two or three, depending on how you make them.

• 30:32Wendy Zukerman?

  I, I love that you were like, so. I went deep undercover. I bought a Prime and I turned it around and I looked at the label.

• 30:42Speaker 04

  And, and of course, you can overdose on caffeine. Uh, the toxic effects are thought to start at 1,200 milligrams, which is about six cans of Prime. And there are case reports of people drinking a bunch of energy drinks and being hospitalized. But here's where things get mysterious.

• 31:01Wendy Zukerman?

  Uh huh.

• 31:02Speaker 04

  There are reports of people, often younger people, dying after drinking less than that, which suggests this isn't just about caffeine. And Professor Sachin Shah saw reports like that in the news and thought.

• 31:19Speaker 05

  Hey, there is, there's something going on here.

• 31:23Speaker 04

  You know, it was actually a little bit sad at points talking to Sachin because he's actually been in touch with the parents of kids who have died after drinking energy drinks.

• 31:31Speaker 05

  Yeah, we've had emails from other countries. One where somebody's like, I have kept the drink that my, my kid drank from the time when they drank it, just in case it helps future scientists. I'm happy to give you that drink.

• 31:48Wendy Zukerman?

  Oh, that's heartbreaking.

• 31:50Speaker 04

  Yes. So Sachin, who's a professor of pharmacy at the University of the Pacific in California, he wanted to know, why would anyone die after drinking a couple of energy drinks?

• 32:01Wendy Zukerman?

  Yeah, yeah.

• 32:02Speaker 04

  So to get to the bottom of it, he did this study where he got people to drink a couple of energy drinks and then looked at what their heart was doing. Because typically what we see in these cases is that someone's heart stops beating shortly after drinking energy drinks.

• 32:17Wendy Zukerman?

  Uh huh.

• 32:17Speaker 04

  So he got these volunteers to come into the lab. He hooked them up to an EKG.

• 32:22Speaker 05

  Many people see this on TV shows where they have somebody in the hospital, they're connected to this.

• 32:26Speaker 04

  Uh, screen, they're lying in the hospital and they show this squiggly line. Yes, yes. That's looking at, that's looking at your heart rhythm. Beep, beep, beep. Yes.

• 32:35Wendy Zukerman?

  Just to avoid us putting the sound effect in.

• 32:38Speaker 04

  Always thinking ahead.

• 32:39Wendy Zukerman?

  Okay, so they've drunk the energy drinks.

• 32:42Speaker 04

  And then he monitored them. And one hour, two hours, four hours, six hours, and 24 hours. And he was looking at this particular part of our heart's rhythm that's called the QT interval, which is, it's basically looking at how long it takes your ventricles to contract after every beat. And if this takes longer than normal, it can throw your heart into something that's called fibrillation, which is like, instead of going squeeze, squeeze, squeeze, your heart starts quivering, like a nervous chihuahua. And the problem with that is that your heart isn't actually pumping out any blood, and you can die.

• 33:21Wendy Zukerman?

  Oh, man. Okay, so did the energy drinks mock up the QT interval?

• 33:29Speaker 04

  So, so, yeah, so you know, what was interesting is in that first study, we found that energy drinks were prolonging the QT interval by 10 milliseconds. A follow-up study he did found this again, that the energy drinks extended the QT interval by, this time, six milliseconds. And Sachin points out that several drugs have been pulled from the market for prolonging the QT interval by six milliseconds.

• 33:54Wendy Zukerman?

  Hmm, wow. Okay, so if I were to drink the equivalent caffeine from what he gave them, but in coffee, would my QT interval be extended like that?

• 34:06Speaker 04

  No, studies have also looked at this for caffeine or for coffee, and they don't find the same thing. And actually, in Sachin's study, in one of his studies, they, they included a caffeinated control, and it didn't do the same thing to people's hearts.

• 34:22Wendy Zukerman?

  So if energy drinks are doing this, why aren't heaps of people, like, getting heart attacks and are dying after drinking energy drinks? I mean, millions of people must be guzzling this stuff. And Only a handful have died or so?

• 34:38Speaker 04

  Yeah, I mean, it's not like anyone in Sachin's study had to be rushed to the hospital.

• 34:42Wendy Zukerman?

  Right, right.

• 34:43Speaker 04

  But the thinking here is that there are some people who could be really vulnerable to this. Like, people who have heartbeats that already have kind of a long QT interval. And then the energy drink might extend it even more. And that could tip you over into Chihuahua territory.

• 34:59Wendy Zukerman?

  Right, right.

• 35:00Speaker 04

  One study actually found this. It gave energy drinks to people with a heart condition like that. And found that the drinks extended their QT interval in such a way, it was actually dangerous.

• 35:12Wendy Zukerman?

  Uh huh. So then, so then can we go back to that point? Like, if it wasn't the caffeine, if it's not the caffeine doing this, then what is it in energy drinks that's, that's causing this?

• 35:26Speaker 04

  Yeah, I mean, in Sachin's study, they tested a couple of different brands. They both had caffeine, taurine, which is an amino acid, and a supplement called glucuronolactone, which is found in a lot of energy drinks, like Red Bull.

• 35:39Wendy Zukerman?

  So this is the ingredients, this is how we get wings, is that right?

• 35:43Speaker 04

  This is the wing recipe, yes.

• 35:46Wendy Zukerman?

  Okay.

• 35:47Speaker 04

  So all this stuff together seemed to extend the QT interval. But then I found this one study that tried to really get to the bottom of which ingredient is the bad guy here. So they basically deconstructed a Red Bull and had people drink a few of the components one at a time while they were hooked up to an EKG, just like Sachin. And after drinking the Red Bull, volunteers had a prolonged QT interval. But none of the individual components did this.

• 36:17Wendy Zukerman?

  What?

• 36:18Speaker 04

  Neither did the combination of caffeine and taurine together. So I asked Sachin about this. What do you think is in these energy drinks that causes these changes?

• 36:26Wendy Zukerman?

  Another question. Science! Um, you know, I was having coffee with my brother the other day, and he said, "There is always a point in a Science vs. episode where the scientist says, 'Dad, we don't really know what's going on.'" And I guess this is that point.

• 36:42Speaker 04

  Yeah, we've arrived at that point in the episode. And, and of course, it's also really hard to say what's going on when this is probably very, very rare, you know? People drink energy drinks all the time and very few people land in the hospital.

• 36:57Wendy Zukerman?

  Okay, so here is what I think I have learned from this episode, Rose Rimla. Tell me how I did.

• 37:05Speaker 04

  Let's hear it.

• 37:05Wendy Zukerman?

  Um, and if I pass the test, I have a good sense of humor. Is that what we learned?

• 37:11Speaker 04

  Yeah, yes. Case closed.

• 37:15Wendy Zukerman?

  Caffeine truly does make me poo. Very quickly. Nice. Um, it can affect your sleep, but very much dependent on genetics. So dare I say, "Listen to your body and not what people online might be telling you about what you should and should not do with caffeine." And meanwhile, it might reduce your risk of depression if you're drinking coffee and tea. What'd you say? Cancer, Parkinson's?

• 37:42Speaker 04

  Diabetes.

• 37:43Wendy Zukerman?

  Diabetes. And, and energy drinks, there is something weird about them. So if you are looking for a boost, it's safer to go with tea or coffee. How'd I do?

• 37:56Speaker 04

  A-plus, people. I'm not surprised. And you, as a prize, I sent a case of Prime to your, uh, house. So.

• 38:06Wendy Zukerman?

  Great.

• 38:07Speaker 04

  Don't drink it all at once.

• 38:08Wendy Zukerman?

  Excellent. Cheers, Rose.

• 38:11Speaker 04

  Cheers.

• 38:12Wendy Zukerman?

  But before you go, Rose. Rose. Rose.

• 38:16Speaker 04

  I'm here, I'm still here.

• 38:17Wendy Zukerman?

  Okay, okay. How many citations are in this week's episode?

• 38:21Speaker 04

  This episode was the first time I've ever opened so many tabs that my browser stopped displaying them. Like, I, I reached the limit of how many tabs I can have open.

• 38:31Wendy Zukerman?

  That is so many tabs.

• 38:34Speaker 04

  It's like getting to the end of your Instagram feed. You're like, oh, no. Um, but, uh, what is in the script is that we have 118 citations.

• 38:43Wendy Zukerman?

  118, okay, yes. And, um, if people want to see these citations, find out where we got all of our info from, where should they go?

• 38:52Speaker 04

  They can click the link in the show notes that will send them to the transcript.

• 38:56Wendy Zukerman?

  Excellent. And I guess while people are scrolling through Instagram and hitting the end, if you have hit the end of your Instagram, you could just come over to Science Versus. Was that a segue of like picking out social media accounts?

• 39:09Speaker 04

  That was pretty good.

• 39:09Wendy Zukerman?

  Thanks.

• 39:09Speaker 04

  Yeah.

• 39:11Wendy Zukerman?

  We are at science@disco Vs. I'm on TikTok at Wendy Zukerman and we will see you next week. Thanks, Rose.

• 39:21Speaker 04

  Thanks, Wendy.

• 39:26Wendy Zukerman?

  This episode was produced by Rose Rimler with help from me, Wendy Zukerman, as well as Nick Del Rose, Joel Werner, and Michelle Dang. We're edited by Blythe Terrell, fact checking by Sarah Baum, mix and sound design by Bumi Hidaka, music written by Bobby Lord, Bumi Hidaka, Emma Munga, and Peter Lennon. Special thanks to all of the researchers that we spoke to for this episode, including Dr. Brian Saunders, Dr. Sergi Ferre, Professor Andreas Heinz, Professor Christine Curran, Dr. Erica Loftfield, Dr. Felix Oberhoffer, Dr. Alan Wayne Jones, and Dr. Vijay Yadav. Extra special thanks to Jason Bitlisil and the Zukerman family. Science Versus is a Spotify Studios original. You can listen to us for free on Spotify

• 40:06Wendy Zukerman?

  or wherever you get your podcasts. We are everywhere that podcasts are. I guess we're in a lot of places. If you are listening on Spotify, follow us and tap the bell icon so you can receive notifications whenever we put out a new episode. And if you like us, wherever you are listening, please give us a five star review. I'm Wendy Zukerman. Back to you next time.

• 40:34Speaker 04

  Now, it's not all fun stuff like rectal probes.

• 40:37Wendy Zukerman?

  Name of your sex tape? It's not all fun and rectal probes?

• 40:42Speaker 04

  No, the sex tape is called All Fun and Rectal Probes.

• 40:51Wendy Zukerman?

  Right.

• 40:51Speaker 04

  We can't only talk about rectal probes in this episode. We also unfortunately have to talk about some unpleasant stuff.