By Laura Smith
Whether it's consumed to enhance performance or as part of the daily diet, caffeine can be a negative for today's competitive athlete. Increasingly, high schoolers are rivaling adults in their caffeine use, downing sodas and visiting coffee shops for frozen or sweetened caffeinated drinks. In addition, many student-athletes turn to caffeine products to enhance their athletic performance.
And while there is laboratory evidence that caffeine enhances performance, athletes who use it as an ergogenic aid need to be educated about the risks.
Structurally, caffeine mimics one of the body's natural chemicals, a neuromodulator called adenosine. Under normal circumstances, adenosine acts as the "brakes" in the central nervous system, inhibiting neuronal firing and neurotransmitter release. As adenosine concentration builds slowly in the body over the course of the day, its "slow down" effect leads to feelings of sleepiness and, eventually, to sleep.
When caffeine is ingested, because it is similar to adenosine, it binds to adenosine receptors and "plugs them up," according to Laura Juliano, PhD, caffeine researcher and Assistant Professor of Psychology at American University. "With caffeine blocking adenosine receptors, adenosine cannot have its normal effect, so you feel less fatigued and more alert," she says.
Caffeine also increases the availability of many neurotransmitters, which can affect the body in several different ways. "Caffeine doesn't target one neurotransmitter—it targets adenosine, and through its effect on adenosine, it affects everything else," Juliano says. With the flood of neurotransmitters and the short-circuiting of fatigue-producing adenosine, it makes sense that most people feel more energized and better able to focus with caffeine, whether they're recalling answers for a physics exam or completing a tough practice.
Why is caffeine so addictive? Researchers recently uncovered at least part of the answer when they discovered that caffeine releases dopamine (the "pleasure and reward" neurotransmitter) in the part of the brain called the nucleus accumbens—an area that plays an important role in all addictive drugs. Researchers believe this may explain why casual caffeine users often become dedicated, and then addicted, users.
When student-athletes become daily caffeine users, particularly with heavy use, both their health and performance may suffer in ways they aren't even aware are happening. One of the biggest risks: Caffeinerisks is that caffeine use disrupts sleep, and student-athletes are often sleep-deprived to begin with.
"High school and college students are notorious for not getting enough sleep, and especially when they are athletes, it's absolutely essential that they get enough rest to repair muscle tissue and perform optimally," Juliano says. "Caffeine increases the length of time it takes to fall asleep and decreases total sleep time."
It doesn't require downing a grande coffee right before bed to see the effect, either. Studies have shown that using consuming a moderate amount of caffeine early in the day can reduce the quality and quantity of that night's sleep.
Another concern involves caffeine's ability to produce anxiety. Again, the effect does not require huge doses. Starbucks reports that its 16-ounce coffee contains 400 milligrams of caffeine—the exact amount researchers administer in the laboratory to induce anxiety, according to Juliano. "There is already a lot of anxiety in the lives of most student-athletes," she says. "And caffeine is going to magnify it."
A student-athlete who has an exam looming, a paper due, and a game coming up may down a mug or two of coffee to make it through the day, then attribute feelings of stress and anxiety to the workload. "In reality, caffeine is probably making them feel much worse, but they don't realize it," says Juliano.
Daily consumption of coffee and colas also deprives the body of calcium, according to Barbara Lewin, RD, LD, who sees professional and student-athletes at a Fort Myers, Fla.-based private practice. "Coffee and colas are high in phosphorus, and the body requires a certain phosphorus-to-calcium ratio," Lewin says. "If your phosphorus intake is high, and you don't ingest enough calcium, your body will pull calcium from your bones. Most student-athletes don't get enough calcium in their diets as it is. Often, when I look at a student-athlete's daily calcium intake alongside their use of coffee and colas, they are in a negative calcium balance."
There are two other nutrition negatives to be aware of. First, since caffeine increases the production of stomach acid, large amounts can induce an upset stomach or acid reflux. Second, while caffeine is no longer believed to be a diuretic, most caffeinated beverages are not particularly good sources of hydration. If they replace water or sports drinks in an athlete's diet, chances of dehydration increase. (See "Does Caffeine Dehydrate?".)
Last but not least, student-athletes who use caffeine daily will build up a tolerance, gradually needing more and more to achieve the same effect. They'll also develop dependence and feel like they need caffeine to function normally. "When it comes to chronic caffeine users, it's often difficult to separate the effect of the drug from the effect of not having the drug," Juliano says. "In other words, they may think caffeine makes them feel and perform better, but in reality, it just keeps them from feeling bad from not having it."
Few sports nutritionists advise college athletes to avoid caffeine altogether. It's simply too pervasive an ingredient in many foods and drinks. But how much is too much?
"If a student-athlete does not want to be physically addicted to caffeine, he or she needs to use well below 100 milligrams a day, which means drinking only one caffeinated soft drink or a very small cup of coffee a day," Juliano says.
For student-athletes who find that recommendation unrealistic, nutritionists advise that they keep their daily intake under 300 to 400 milligrams a day. While this amount does cause dependence on the substance, other side effects, such as anxiety, sleeplessness, and digestive disturbance, generally don't occur. Staying under 400 milligrams requires limiting intake to about two cups of coffee or three caffeinated soft drinks a day.