How Much Caffeine Are You Consuming?

If you've been drinking green tea for its health benefits, you may be in for a jittery surprise: ounce for ounce, it has more caffeine than a can of Classic Coke. Trying to stay awake? Many energy drinks are all hype, with less caffeine per can than a cup of regular coffee.

Related: 7 myths about caffeine

According to Energy Fiend, a site that tracks listed and unlisted caffeine content in food and drinks, some of the most popular drinks out there have far more -- or far less -- caffeine than you might think.

In addition to checking out the caffeine content of sodas, coffees, and teas, the site also analyzed energy drinks and energy shots. Those concentrated shots, obviously, pack the biggest caffeine punch: 5-hour energy has about 69 milligrams of caffeine per fluid ounce, and Redline Power Rush has about twice as much. Among the beverages, Monster M3 Energy Drink delivered 150 mg of caffeine per 5-ounce can (that's 32 mg per fluid ounce), and Red Bull, which once was the ultimate go-to energy drink, has just 9.5 mg per ounce -- about as much as a Starbucks latte.

Related: Caffeine in pregnancy won't harm offspring, study says

Good old fashioned coffee clocked in at anywhere from 51.3 mg of caffeine per ounce (in espresso form) to 0.3 mg per ounce for instant decaf (yes, decaf). And the caffeine content can depend on how the coffee is prepared: Drip coffee has 18.1 mg per ounce, brewed coffee has 13.4 mg per ounce, and instant coffee has just 7.1 mg per ounce. Your mileage may vary among the coffee-shop giants, too: Dunkin' Donuts coffee has 13.2 mg of caffeine per ounce, compared to 15 mg for Caribou Coffee, 9.1 mg for McDonald's, and 20.6 mg for the regular brew at Starbucks.

Soda drinkers who want to avoid caffeine should stick to the classics: 7Up, Fresca, Ginger Ale, and Sprite all have no caffeine. But all root beers aren't created equal; while A&W is caffeine-free, Barq's has 1.9 mg per ounce. Classic Coca-Cola had 2.8 mg per ounce, Pepsi had 3.2 per ounce, Diet Coke has 3.8 mg per ounce, and the myth of Mountain Dew is debunked, given that it has less caffeine than Diet Pepsi Max -- 4.5 mg per ounce, compared to 5.8 mg. (You can look up the caffeine content of your favorite beverage here.)

Moderate amounts of caffeine (200 to 300 mg per day) aren't harmful, according to the experts at the Mayo Clinic. "Caffeine stimulates the central nervous system, alleviating fatigue, increasing wakefulness, and improving concentration and focus," they explain.

But knocking back 500 to 600 mg worth every day (that's about four cups of regular coffee, or two to three energy shots) can lead to a host of physical problems.

"Some research has linked high doses of coffee to infertility and increased risk of hip fractures in older women," Keri M. Gans, MS, RD, CDN told Prevention magazine. "If you stop drinking coffee abruptly, you may experience irritability, fatigue, headaches, and even depression."

Copyright © 2012 Yahoo Inc.

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