5 Popular Energy Drinks: Are They Safe?

My buddy Brian brags about his morning routine: On the way to work, he swings by a local convenience store and picks up a large cup of coffee, lunch, and a can of Amp Energy. His theory: The coffee jumpstarts his morning, lunch fuels his afternoon, and the energy drink—which he downs in the early afternoon—propels him past his 5 p.m. finish line.

This all sounds plausible, but here's the problem: My friend is a good 30 pounds overweight. In other words, he's already consuming too much energy. So adding 220 calories and 58 grams of sugar to his day, in the form of an energy drink, doesn't make a whole lot of sense.

For most Americans, it's not a lack of sugar that makes us tired during the day—it's the fact that we're already consuming too much. Sugary foods and drinks cause blood sugar to spike, and you feel energized. To compensate, your body releasesinsulin, which quickly lowers blood sugar levels, causing you to "crash" and feel tired. If you indulge your sweet tooth throughout the day, your blood sugar yo-yos all day long. It's no wonder Amp revs up my buddy's afternoon—the sugar blast pulls him out of his post-lunch crash.

Americans will spend around $9 billion on energy drinks this year, which is why manufacturers haven't strayed far from the best-selling recipe they used when the first energy drinks took off a dozen years ago. It's a formulation that includes a hefty dose of caffeine and sugar combined with smaller amounts of natural substances like guarana, ginseng, and taurine that—the labeling promises—may sharpen your mind and improve your overall health. (Here are more foods with amazing—and scientifically proven—health benefits: Check out the 40 Foods with Superpowers.)

But do these beverages really work? To help you separate the science from the sales pitch, we analyzed five key ingredients in the market's most popular potions.

CAFFEINE
What is it? A chemical compound that stimulates your central nervous system. Most energy drinks contain between 140 and 170 milligrams (mg) of caffeine in a 15- or 16-ounce can.

Does it work? Java junkies certainly think so. As for the science, an Austrian study showed that men who swallowed 100 mg of caffeine had a bigger boost in brain activity after 20 minutes than those who took a placebo. Plus, a new University of Chicago study found that a 200 mg jolt made fatigued people feel twice as alert as noncaffeinated participants. "Caffeine indirectly affects many different neurotransmitters," says Andrew Scholey, Ph.D., an herb and nutrition researcher at Australia's Swinburne University of Technology.

Is it safe? The most caffeine-packed energy drink contains the equivalent in caffeine of about two 8-ounce cups of coffee. If downing that much joe doesn't make you jittery, then quaffing a can shouldn't pose a problem. Of course, if you combine that with other caffeinated beverages throughout the day, then the sum total stimulation could cause headaches, sleeplessness, or nausea. On the other hand, if you're not a regular coffee or cola drinker and you battle high blood pressure, the occasional energy drink could be trouble. Researchers in Finland reported that the caffeine in two to three cups of coffee can cause blood pressure to spike by up to 14 points.

GLUCOSE
What is it? Sugar. Sucrose, another ingredient you'll often see on energy drink labels, is a combination of fructose (the natural sugar found in fruit) and glucose. Many energy drinks contain 50 to 60 grams (g) of glucose or sucrose in a 16-ounce can.

Does it work? Your body runs mainly on glucose, so topping off your tank with the sweet stuff should theoretically provide an instant boost. And in fact, a study in the Journal of Applied Physiology found that men who guzzled a 6 percent glucose drink were able to bicycle 22 minutes longer than those who went sans the extra sugar. Where glucose won't help, however, is with the fog of fatigue from too littlesleep. A 2006 British study determined that sleep-deprived people who drank liquid glucose exhibited slower reaction times and more sleepiness after 90 minutes.

Is it safe? Dumping empty calories down your gullet is never a great idea, and some energy drinks contain nearly as much sugar as a 20-ounce soda. Then there's the fact that a sudden infusion of glucose can cause your blood sugar and insulin levels to skyrocket, signaling your body to stop incinerating fat. A 2006 New Zealand study reveals that caffeine combined with even the 27 g of sugar in, say, an 8.3-ounce Red Bull may be enough to temporarily inhibit your body's ability to burn lard. Speaking of sugar-laden drinks that are guaranteed to bloat your belly, make sure nothing from this list ever passes your lips: the 20 Worst Drinks in America!

GUARANA
What is it? A South American shrub. One seed has a caffeine content of 4 to 5 percent, while a coffee bean has 1 to 2 percent. Guarana is found in such energy drinks as Rockstar, Amp Energy, and Vault Red Blitz. The amount in a 16-ounce drink ranges from a minuscule 1.4mg to as much as 300 mg. And that inconsistency is part of the problem with energy drinks.“The dosages of the herbs added to the energy drinks are usually so low as to have virtually no impact,” says Kevin A. Clauson, PharmD, associate professor at Nova Southeastern University, Ft. Lauderdale. “It probably doesn’t have much of a safety risk, but it also won’t do you any good.”

Does it work? Perhaps, if you drink enough of it. A study in the journal Appetitereports that people who took 222 mg of guarana felt slightly less fatigued and were up to 30 milliseconds faster on a reaction-time test than those who popped a placebo. Some scientists attribute guarana's effect solely to its caffeine content, but Scholey isn't so sure. His team found energizing effects with doses just under 40 mg, which contain very little caffeine. That means there's probably something else in guarana that produces a stimulating effect on its own or that bolsters the effect of the caffeine, he says.

Is it safe? Scientists at Florida's Nova Southeastern University recently conducted tests and concluded that the amounts of guarana found in most energy drinks aren't large enough to cause any adverse effects. That said, there's still a question mark regarding the safety of higher levels, which could conceivably be consumed by downing a few energy drinks in a brief time span.

GINSENG
What is it? An extract made from the root of the ginseng plant. Panax ginseng is the species most commonly used. The ginseng content in energy drinks, including Starbucks Doubleshot Energy+Coffee, typically ranges between 8 mg and 400 mg in 16 ounces.

Does it work? Not if you're hoping for energy to burn. A review inAmerican Family Physician determined that ginseng doesn't enhance physical performance. But there is an upside: It may boost your brainpower. Scholey and his colleagues found that people who swallowed 200 mg of the extract an hour before taking a cognitive test scored significantly better than when they skipped the supplement. They also felt less mental fatigue. Ginseng may work by increasing the uptake of blood glucose by cells in the brain and elsewhere, says Scholey. However, the right amount is essential—only two of the eight major energy drinks we examined contained that optimal dose of at least 200 mg.

Is it safe? Since the amount of ginseng in an energy drink is minimal, harmful effects are unlikely. And while there have been some reports of negative side effects from ginseng—diarrhea, for example—Scholey points out that those occurred in people taking 3 g a day. One caution: If you're on any medications, check with your doctor before knocking back an energy drink. Ginseng has been shown to interact with blood-thinning drugs like warfarin, potentially altering their effectiveness.

TAURINE
What is it? One of the most abundantamino acids in your brain, where it can act as a neurotransmitter—a chemical messenger that allows your cells to communicate with one another. You'll find anywhere from 20 mg to 2,000 mg of taurine in most 16-ounce energy drinks, including Amp Energy, Red Bull, and 5-Hour Energy.

Does it work? Scientists aren't sure, but it doesn't seem likely. When taurine is dumped into your bloodstream—when you down a Red Bull, for instance—it can't pass through the membranes that protect your brain, says Neil Harrison, Ph.D., a professor of pharmacology at Weill Cornell Medical College. But even if it could, Harrison's research suggests that taurine might behave more like a sedative than a stimulant. When he and his team applied the amino acid to the brain tissue of rodents, they discovered that it mimicked a neurotransmitter called gamma-aminobutyric acid, or GABA, a chemical that slows brain activity.

Is it safe? Taurine is probably fine in small doses, but chug too many energy drinks and the picture becomes less clear. According to a recent case report from St. Joseph's Hospital in Phoenix, Arizona, three people had seizures after drinking approximately two 24-ounce energy drinks in a short period of time. However, the researchers don't know whether to blame the taurine or the caffeine, or what role preexisting health conditions may have played. The fact is, there's been little research on taurine consumption in humans, so it's impossible to conclude whether it's safe to consume in high doses. Of course, there's no strong evidence to support its role as an energy booster, either.

So what's the bottom line: If you feel you need a boost, reach for unsweetened beverage that contains only caffeine, such as black coffee from Starbucks or Dunkin' Donuts. Both have zero grams of sugar, between 150 and 260 mg of caffeine, and less than 20 calories—all for about 2 dollars.

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