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DAVID GREENE, HOST:

I have this image of many of you sipping from a big cup of coffee right about now. Maybe you go to the same coffee shop every day, order the exact same thing. But you know how some days, that same cup of coffee just doesn't quite do it for you? And even after drinking it you still feel like this...

(SOUNDBITE OF RELAXING MUSIC)

GREENE: And then there are those days when that same cup makes you feel like this....

(SOUNDBITE OF DRIVING INDUSTRIAL MUSIC)

GREENE: If your coffee didn't wake you up, that probably did. Well, we wanted to understand this whole phenomenon - this thing called caffeine that so many of us drink every single day without even thinking about it.

We spoke to Murray Carpenter. He's the author of a new book, called "Caffeinated: How Our Daily Habit Helps, Hurts, and Hooks Us." We started by asking him how much caffeine is in our daily cup of coffee.

MURRAY CARPENTER: It's almost impossible to know. The caffeine levels in coffee vary widely. So you can get the same brew, the same preparation from the same café two days in a row, and the caffeine levels might be twice as high one day versus the next.

GREENE: And tell us what this stuff is that we're putting into our bodies. What is caffeine?

CARPENTER: In its essential form, it's a bitter white powder. It's a chemical that's naturally found in plants. Its primary function seems to be as an insecticide. And over the years, people have found, you know, independently, that if you consume it, it has a stimulating effect. And that's basically how we've come to use caffeine over the years.

GREENE: OK, so the stuff is produced naturally. And I was interested, as you took a sort of on a tour of caffeine, when they were coming up with decaffeinated coffee, they actually heated up coffee beans to burn out the caffeine. And you were left with this residue of caffeine.

CARPENTER: Yeah, so that that considered, you know, naturally extracted caffeine. And that is one of the two ways that we get caffeine powder for use in soft drink. The other way is to synthetically produce caffeine in pharmaceutical plants, and this is the way most of our caffeine is produced now.

GREENE: And a lot of this is produced, this synthetic caffeine, in China. You've visited a pharmaceutical plant - or at least close to one, you weren't allowed in - and it sounded like kind of a scary looking place.

CARPENTER: Yeah, I mean sketchy, yeah. I mean it was not what I expected. It was sort of a rundown industrial park. And this was the world's largest caffeine plant.

GREENE: Let me ask you about how much you should or shouldn't consume. There was some scary stuff in this book. You brought up the story of a college student. Tell me what happened there.

CARPENTER: Well, he basically was at a party and he took a couple of spoonfuls of caffeine and chased them with an energy drink, went into seizures and died. And this is one of the ways, I think, in which we underestimate caffeine's power. And a tablespoon, about 10 grams, will kill you. So I think a lot of times we think of it as, you know, a drug that's not particularly powerful but it really has to do with the dose.

GREENE: Why don't we think of caffeine as a drug?

CARPENTER: Its fraud, isn't it? I mean on one hand, caffeine makes you feel wonderful, and most of us use it every single day. On the other, I think we have unease about being dependent on a psychoactive chemical. And so, I think it's much easier for us to think of it as just: Oh, I like my coffee or I like my Diet Coke, rather than I needed those of caffeine right now.

GREENE: Is it, over the long term, dangerous? I mean, as far as your research has taken you, you know, you're drinking three or four cups of coffee a day.

CARPENTER: No. I mean for people who think who are using caffeine moderately, three or four cups a day, it's probably perfectly healthy. And, you know, there are some indications that we may even get some benefit out of long-term caffeinated coffee drinking.

GREENE: What surprised you the most as you dug into the subject so intensely?

CARPENTER: I'd say two things. One is sort of the scope and scale of the caffeine industry. If you just look at carbonated soft drinks and coffee together, that's $100 billion annually. Something else that really surprised me, our grandparents tried twice as much coffee as we do. Coffee consumption peaked around 1950 in this country. So, you know, despite the Starbucks on every corner - the sort of conspicuous coffee culture that we have today - we're not drinking as much coffee as our grandparents did and they were more caffeinated than we are.

As coffee consumption declined, carbonated soft drinks grew. They have less caffeine but they've become our favorite caffeinated beverage.

GREENE: You know, we think of Coke and Pepsi, and certainly those soft drinks we know how caffeine. But I was kind of surprised by some of the soft drinks that, you know, I sort of didn't really think of as being caffeinated. There's a lot of caffeine in a lot of these drinks.

CARPENTER: Right, so Sunkist is one that people don't think of as being caffeinated.

GREENE: The orange soda.

CARPENTER: The orange soda, sure. And one way to look at it is eight of the top 10 selling soft drinks in this country are caffeinated. All of the top five are caffeinated. And if you look at, say, Coke, Diet Coke, Pepsi, Mountain Dew a Dr. Pepper, the only common denominator - besides carbonated water - is caffeine.

GREENE: And labeling can be an issue. You had quite a story about some orange soda. Tell me what happened there.

CARPENTER: Yeah, I mean you might call it super Sunkist.

(LAUGHTER)

CARPENTER: These were sodas that should of had 41 milligrams of caffeine per 12 ounce serving. But instead, they were blended with six times the labeled amount of caffeine, so 240 milligrams per bottle. And 4,000 cases of the super caffeinated Sunkist went out there. They started getting consumer complaints and agreed with FDA to have a voluntary recall. But my impression is probably a lot of people who consumed this, and had some funny experience with caffeine, probably didn't know exactly what was going on.

GREENE: What is your guidance for people who drink coffee or drink Diet Coke, where you start risking having too much of the stuff?

CARPENTER: So if you have troubles sleeping, well, caffeine is a well-known sleep disruptor. So I would certainly urge anyone who has trouble sleeping to experiment with, you know, moderating or eliminating their caffeine use just to see if it helps. And one of the other well-known risks of using too much caffeine is anxiety. A lot of people who are anxious learn not to use caffeine. The shorter answer is I think we should really try to pay more attention to caffeine use and how it affects our brains and our bodies.

GREENE: Murray Carpenter, you have taught me a lot this morning including the drinking some caffeine in moderation is not necessarily the worst thing. So I'm going to get back to my cup of coffee. You do the same. Thank you so much for joining us.

CARPENTER: Well, thanks for your interest.

(SOUNDBITE OF A SONG)

UNIDENTIFIED WOMAN: (Singing) Well, caffeine, caffeine, you know that it's our friend. I got to have my coffee or I'll turn and leave. Put it on the rocks or straight up with cream, you know, I want...

GREENE: You're listening MORNING EDITION from NPR News. I'm David Greene.

RENEE MONTAGNE, HOST:

And I'm Renee Montagne.

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