Source: U.S. Department of Health & Human Services, National Institutes of Health, Office of Dietary Supplements (2017).

Caffeine is a stimulant in beverages (like coffee, tea, and energy drinks) and in herbs (such as guarana and kola nut). Caffeine is also added to some dietary supplements. Moderate amounts of caffeine might increase your energy levels and reduce fatigue for several hours.

DOES IT WORK? Caffeine might improve endurance, strength, and power in team sports. It’s most likely to help with endurance activities (such as distance running) and sports that require intense, intermittent effort (like soccer and tennis). Caffeine doesn’t help with short, intense exercise like sprinting or weightlifting. People have different responses to caffeine. It doesn’t boost performance in everyone, or may only slightly boost performance.

The usual dose of caffeine to aid performance is 2 to 6 milligrams per kilogram of body weight or about 210 to 420 mg caffeine for a 154-pound person. (By comparison, a cup of coffee has about 85 to 100 milligrams of caffeine.) Taking more probably doesn’t improve performance further and can increase the risk of side effects.
IS IT SAFE? Caffeine intakes of up to 400 to 500 milligrams a day seem safe in adults. Teenagers should limit their caffeine intake to no more than 100 milligrams a day. Taking 500 milligrams or more a day can reduce rather than improve physical performance, disturb sleep, and cause irritability and anxiety. Taking 10,000 milligrams or more in a single dose (one tablespoon of pure caffeine powder) can be fatal.
BOTTOM LINE Sports-medicine experts agree that caffeine can help you exercise at the same intensity level for longer and reduce feelings of fatigue. They suggest taking 2 to 6 milligrams per kilogram of body weight 15 to 60 minutes before you exercise. The National Collegiate Athletic Association and International Olympic Committee limit the amount of caffeine that athletes can take before a competition.
REMARK Many performance supplements in the marketplace contain more than one ingredient, and ingredients can work differently when they’re combined. Because most ingredient combinations have not been studied, it is not known how effective or safe they are in improving performance.

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