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9 Things You Should Know About Your Caffeine Habit

A chat with Murray Carpenter, author of the book "Caffeinated: How Our Habit Helps, Hurts, and Hooks Us"

The following article first appeared on Mother Jones. For more great content, click here to subscribe. 

Even if you're not among the  63 percent of Americans who drink coffee every day, caffeine is hard to avoid. It's all over your corner store, from energy drinks to colas and bottles of iced tea to cans of Starbucks " Refreshers." For a while there, it was looking like even  your gum was going to be caffeinated.

But despite its pervasiveness, we still understand little about the stuff. It doesn't help that the beverage industry hopes to keep it that way; for instance, though energy drink sales have skyrocketed in recent years, their manufacturers aren't required to label how much caffeine their products contain. Meanwhile, emergency room visits related to energy drink use  increased more than tenfold between 2005 to 2009.

In his new book,  Caffeinated: How Our Daily Habit Helps Us, Hurts, and Hooks Us, out March 13, journalist Murray Carpenter takes on this mysterious substance. He toured Colombian coffee fields, Chinese tea lounges, and factories pumping out synthetic caffeine for soft drinks, interviewing FDA regulators, industry spokesmen, neuroscientists, and cacao cultivators. I chatted with Carpenter about how much caffeine is healthy, where the industry stands on labeling, and the most pretentious coffee preparation he's observed. Here were some of the biggest takeaways.

1. A healthy daily dose of caffeine can be very different depending on who you are.

"When doctors talk about moderate caffeine use, they talk about somewhere in the range of 300 to 400 milligrams. Most coffee drinkers tend to be in that range. Beyond that: 300 milligrams to one person might be perfect, but it might send another one through the roof. It varies so much, depending on your size, if you're a smoker, if you have a genetic predisposition to metabolize caffeine slowly. It would be foolish to say X is the perfect amount or X is too much.

"Women on birth control metabolize caffeine twice as slowly—which means they get double the jolt from the same cup of coffee. And smokers metabolize it twice as fast. There are some people with a genetic predisposition to metabolize caffeine slowly. Those are the people who are going to be super sensitive to caffeine."1. A healthy daily dose of caffeine can be very different depending on who you are. 

2. There's no standard amount of caffeine in each cup of coffee—even within the same brand. 

"Starbucks gives an approximation of 20 milligrams per ounce. One 16-oounce cup of Starbucks puts you at about 320 milligrams of caffeine. One 16-ounce cup of Starbucks is for many Americans a good daily dose of caffeine.

"One researcher found that a 16-ounce cup had 560 milligrams of caffeine. The researcher, Bruce Goldberger,  went to the same Starbucks and ordered the same blend of coffee for six days, and found that the levels varied more than twofold. He's not the only one to have found those things. Even espresso shots, which are much more regimented, can vary."

3. Caffeinated beverage manufacturers are not required by the Food and Drug Administration to label how much caffeine is contained in their product.

"If you market a product as a food or a supplement, they still don't have a requirement that you label the amount of the quantity of caffeine in the product. There's some voluntary labeling initiatives underway: The American Beverage Association has recommended bottlers do that, but you can still find energy drinks that don't tell you how much caffeine is in them.

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