Good news for java junkies: You don't have to skip your caffeine fix to get in a good workout — even in the hot summer months when coffee's widely believed to promote dehydration.
What's more, a caffeinated beverage may actually help you exercise longer.
"For years, people have believed that consuming caffeine would dehydrate the body or result in an electrolyte imbalance or that it might affect body temperature and have a negative impact on heat tolerance during exercise," says Lawrence Armstrong, a professor of exercise physiology at the Human Performance Laboratory at the University of Connecticut in Storrs.
"Our research indicates that none of these concerns is valid," he says.
Fitness experts and dietitians have long advised that exercisers drink up before and during physical activity — but avoid caffeine.
Turns out, though, there's no convincing evidence to support this recommendation, says Armstrong, who published an article on the subject in the July issue of Exercise and Sport Sciences Reviews, a journal of the American College of Sports Medicine (ACSM).
Armstrong and his colleagues reviewed more than a dozen studies and concluded that moderate caffeine consumption — up to about 500 milligrams a day — did not adversely impact exercise. A typical 8-ounce cup of coffee contains 150 milligrams of caffeine while a 12-ounce regular soda has 30 to 50 milligrams.
While caffeine is a mild diuretic — meaning it briefly increases urine production — moderate amounts are not enough to interfere with a workout, Armstrong says. "It doesn't mean that one is dehydrated," he explains. "Dehydration is about the balance of fluid intake and fluid loss."
Little is known about the exercise impact of consuming more than 500 milligrams of caffeine.
The new study is the latest good news about caffeine and exercise. A recent study published in the Proceedings of the National Academy of Sciences found that a combo of the two helped fight skin cancer in mice.
Previous studies also suggest that a java jolt may even boost performance during activities lasting longer than 30 minutes by enabling exercisers to work out longer. In fact, caffeine was once outlawed at the Olympics because of its performance-enhancing effects.
It's not exactly clear why caffeine helps, but Armstrong and others believe the same mental pick-me-up that helps you get your day started or make it through a boring afternoon at work also may help exercisers fight fatigue and thus go longer. Another theory is that caffeine helps the body turn fat into fuel for longer workouts.
Tara Gidus, a sports dietitian in Orlando, Fla., agrees that caffeine doesn't live up to its reputation as a workout wrecker, at least when it's consumed in moderation.
And she notes that exercisers tend to build up a tolerance to caffeine's effects. "An athlete who is used to consuming caffeine regularly may not experience the same diuretic effect as an athlete who doesn't consume caffeine often," she says.
Larry Kenney, a professor of physiology at Penn State University in University Park and a spokesperson for the ACSM, emphasizes that all exercisers — caffeine addicts or not — need to make sure they stay properly hydrated by replacing lost fluids, especially when it's sizzling outside. How much to drink varies from one person to another.
"Athletes should customize their fluid intake based on their individual sweating rate," Kenney says.
To find out how much you need to drink, weigh yourself before and after exercise a few times, Kenney advises. This will tell you how much water you're losing so you can determine how much fluid you need to compensate for the loss. For every kilogram (2.2 pounds) you lose through sweating, you'll need to drink 1 liter (33.8 ounces) to make up for it.
If you're engaging in endurance races or other activities that last an hour or more, consider a sports drink with sodium that replaces lost electrolytes and provides carbohydrates for fuel, he says.
And after your workout, don't feel guilty about hitting the local coffee bar and indulging in your favorite drink — so long as it's not loaded with sugar and topped with whipped cream.