Caffeine: How Our Favorite Drug Affects Us

As I'm writing this, I'm hitting my mid-afternoon slump. And it's Friday, no less. The time seems perfect for a cup of coffee. And now, because caffeine was the topic on KQED's Forum this morning, I know how and why caffeine is an apparent energy booster.

"Its primary role is a simple one," said Forum guest Murray Carpenter. He's the author of Caffeinated and is full of facts about the "bitter white powder." Let's start with the biochemistry: caffeine blocks a neurotransmitter called adenosine. This is the signal that tells you that you are drowsy. When you consume caffeine, it blocks adenosine from sending the "fatigue" message. "Fully 50 percent of the receptors are blocked" after we consume caffeine, Carpenter explained, "and it's that simple trick that allows caffeine to do its work."

But caffeine has another role that I had never heard of: it's a natural pesticide. If insects consume a caffeinated plant, they become paralyzed and die. Odd that it works so differently on humans.

The Food and Drug Administration (FDA) labels caffeine as both a drug and a food additive, but it turns out there's no labeling required so we can all might know how much caffeine we're getting.  In addition, there's tremendous variability about how much caffeine you might be consuming. While colas might have a predictable amount of caffeine, coffee does not. Carpenter cited research showing that a coffee from Dunkin Donuts, for example, had 160 milligrams of caffeine, where as Starbucks was much higher.

But even at Starbucks, Carpenter cited a study where a Florida researcher went to the same Starbucks several days in a row and bought the same size and blend of coffee. He found that one cup had as little as 240 mg of caffeine but another had 560 mg. While ratio of beans to water can cause variability, "the other factor is that (coffee beans are) a natural plant with varying levels of this chemical in it. It could be the growing conditions, rain fall, altitude is going to affect the caffeine concentration."

While caffeine may be a drug, Carpenter said it has not been connected to any serious health conditions (for the overwhelming majority of users; one ER doctor who called in said he'd once treated a woman who consumed 44 cups of coffee a day. Please use common sense.) But caffeine is connected to some more minor conditions: anxiety and sleeplessness. If you're having trouble sleeping, you might think about reducing your caffeine consumption.

Carpenter said research has shown that teenagers' consumption of caffeine has gone up in kids ages 12 to 16. "If you would like your teen to sleep better, it's worth being very aware of their caffeine consumption," Carpenter warned. Those on the younger end of the "12 to 16" age range are likely to be significantly smaller than adults. Remember that a large coffee is likely to affect a smaller body differently than that of an adult.

Parents may be able to relax a little around caffeinated energy drinks. Carpenter asserts that a product like Red Bull, for example, does not have as much caffeine as people seem to think. It compares to a 5-ounce cup of coffee or a single shot of espresso.

Nor surprisingly, there are variations in how people metabolize caffeine. Smokers burn through caffeine twice as quickly as non-smokers, "so they'll need twice as much caffeine to get the same boost as non-smokers," Carpenter says. Meanwhile, women on birth control pills metabolize caffeine more slowly. So they'll need about half as much caffeine to get the same effect.  "There really are quite a number of variables here. So you add those on to genetic variability and the variability that you know exists in coffee, you really have quite a range, a spectrum of how the same amount of caffeine can influence every different person," Carpenter said.

Curiously, light roasted coffees have more caffeine than dark roasted ones. Carpenter explained that some of the caffeine is roasted away during the roasting process. The longer you roast, the less caffeine you get.

One final note: don't believe that a cup of coffee sobers up someone who is drunk.  "What caffeine's allowing a drunk to do is have more energy to do silly things," Carpenter said, such as drive a car.

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