Liquid Perk-Me-Ups

Ever since Red Bull flew onto US shelves in 1997, energy drinks, in their skinny bullet-shaped cans, have zoomed up the stratosphere of beverage sales. The $3.4 billion-a-year industry grew by 80 percent in 2005, according to Beverage Digest. Never mind that these drinks are expensive and not particularly tasty. Their success is based on a tantalizing promise: A magic potion that will wake you up and sharpen your mind.

But some European countries still haven't approved sales of Red Bull and similar drinks because of their high level of caffeine and poorly understood additional ingredients. So should you reach for one when you are in desperate need of a pick-me-up, or turn to old standbys such as coffee or cola?

It would help if we understood all those mystery ingredients. One additive in energy drinks, taurine—a nonessential amino acid—is included in such small amounts that it doesn't add harm or benefit, says Liz Applegate, Ph.D., director of sports nutrition at the University of California at Davis. But the herb guarana, another common additive, has stimulatory effects. That means it adds even more to the drink's already strong caffeine jolt, which could push you over the line between alert and jittery. The B vitamins in energy drinks have not been proven to give people more energy. "The amount is overkill," Applegate says of vitamin B levels in these drinks, which means you are paying for something your body will simply rid as waste.

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A research review put out by UC Davis found that most of the other exotic additives in energy drinks such as carnitine and panax ginseng haven't been studied sufficiently, and so certainly can't be counted on to provide the benefits touted on labels (more endurance, better sexual performance, for example). The review did find limited evidence that energy drinks can improve physical and mental performance, and the driving ability of those sleepy at the wheel, but whether these effects are due to the caffeine or to the combination of the caffeine and other ingredients is not known.

The simple secret to energy drinks' reviving effects, then, is a lot of caffeine (and sometimes a lot of sugar, too). The caffeine content of energy drinks ranges from 72 to 294 mg per bottle. But a much smaller amount—30-35 mgs, which is comparable to what's in most sodas—is probably enough to give you a jolt, Applegate says. If you're accustomed to more caffeine, however, you will need more to perk you up. The good news is that consuming up to 400 mg of caffeine a day doesn't cause harmful health effects for most people. (Pregnant or nursing women, adolescents, and children should take in less than 300 mgs per day.)

More than 400 mgs of caffeine a day, however, can cause dependency, Applegate warns, which means that without your afternoon Monster Energy or Rockstar, you could feel headaches or other uncomfortable symptoms. Too much caffeine can also aggravate heart troubles and anxiety issues, raise your blood pressure, and cause irritability and sleeplessness.

Those looking for a late-night rush should note that mixing energy drinks with alcohol is a dangerous strategy. The stimulating effects made research subjects believe they weren't intoxicated, even though they performed just as poorly on tests of motor coordination and reaction time as they did when drinking alcohol alone.

While you're busy assessing caffeine content, don't forget to count calories, even in sugar-free versions of your favorite energy drink. "I see all my students coming to class with those skinny cans. They're taking in more than 400 calories just to get their jolt. That's 20-30 percent of their daily recommended intake of calories, without much in the way of nutrients." Especially if you are trying to lose weight, skip the energy drinks and have a strong cup of coffee with an artificial sweetener. Another point in favor of coffee: A typical serving with 200 mg of caffeine is not dehydrating, contrary to popular belief, Applegate says.

If you prefer soda to tea or coffee: citrus-flavored sodas have higher caffeine content than classic colas, report researchers from Auburn University. While a 12-ounce bottle of Diet Pepsi has 36.7 mgs of caffeine, for example, Diet Mountain Dew has 55.2 mgs. (A cup of coffee has about 80-100 mgs, while a cup of tea has 60-80 mgs.)

Finally, you can choose other completely safe and caffeine-free alternatives to energy drinks when you're fighting to keep your eyes open. "I'd recommend walking around your desk and drink sparkling water," says Applegate. And if you find yourself taking in caffeine all day long, she says, you need to address the underlying problem: Get more sleep.

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