Caffeine is the one compound with good scientific evidence to support its use as an athletic-performance enhancer. Taken in moderate doses, it’s relatively safe. Caffeine is the only substance for which the International Olympic Committee has set an acceptable level on urine samples, less than 12 micrograms per milliliter. A higher amount will bar an athlete from competition.
Caffeine’s positive effect on athletic performance is most significant for endurance events such as long- distance running, cycling and swimming. Normally, after 30 minutes of exertion glycogen (the body’s most immediate source of glucose for energy) begins to deplete. Caffeine can slow the depletion of glycogen. At an intense pace, glycogen will not run out for one or two hours, but once it does, you can “hit the wall.” By preserving glycogen stores longer, you can potentially increase your exercise time by 20 percent, or perhaps finish a race a little faster. The exact reason for this is under debate, but in some athletes caffeine stimulates earlier and greater use of fat burning for energy.
Performance in short-duration, high-intensity or strength events isn’t enhanced by caffeine. The exception may be caffeine’s central nervous system stimulation that might help in events which have rapidly changing circumstances that need quick reactions and sudden alterations of body movements. On the other hand, you would want to avoid caffeine for events that require a steady hand.
The other potentially positive effects of caffeine for exercise include decreased awareness of feeling tired, mental alertness and improvement in mood to help you maintain a workout program.
But caffeine definitely has its downside. There are important side effects of caffeine that can be quite detrimental to performance and if not attended to can be harmful. Performance-enhancing doses of caffeine cause you to urinate with greater frequency and with higher volumes. The diuretic action of caffeine needs to be balanced by drinking plenty of non-caffeinated beverages before, during, and after exercise. Some athletes get quite restless and nervous with any caffeine. Caffeine even in small amounts can cause insomnia.
The usual recommended caffeine dose is 250 to 500 milligrams taken one hour before an event. I suggest starting at a dose in the lower range, about 300 milligrams, the amount in two cups of strong regular coffee, one to two hours before exercise. A person who never drinks coffee may need less, while someone who drinks two or more cups daily might need more.
Athletes required to provide urine testing must be very careful about how much caffeine they consume. Caffeine is present in many teas, sodas, chocolate, energy supplements and over-the-counter medicines. The amount of caffeine can quickly add up and result in disqualification from competition. Doses above those recommended can decrease performance.
Next week: The most popular supplements promoted as ergogenic aids.
Dr. Howard LeWine is a member of the Harvard Medical School faculty and practicing internist with Harvard Vanguard Medical Associates, and Brigham and Women’s Hospital, Boston. He serves as chief medical editor of Internet publishing at Harvard Health Publications.
