| Caffeine is one of the most widely used stimulants in the world. It occurs naturally in the foods and beverages such as coffee, tea, soft drinks, chocolate and cocoa. The average caffeine consumption in the United States is approximately 200 mg or equivalent to 2 cups of coffee a day. Ten percent of the population ingests more than 1000 mg per day. Caffeine is also added to several over-the-counter medicines such as some weight-loss products, pain medicines, and cold remedies.
Caffeine acts as a stimulant on the central nervous system, which causes the heart rate and blood pressure to increase. After having caffeine, an individual may temporarily feel more awake and energetic. Caffeine also acts as a diuretic, which causes the kidneys to excrete more urine.
Side effects of caffeine include anxiety, jitters, inability to focus, irritability, insomnia, gastrointestinal unrest and nervousness. With higher doses, the risk of irregular heart beats increases. In addition, recent research has found that caffeine may cause miscarriage or slow growth in a developing fetus in pregnant women. It has also been associated with an increased risk of osteoporosis and bone fractures in postmenopausal women.
How does caffeine affect performance in exercise and sports? Caffeine is often referred to as a nutritional ergogenic aid, but it has no nutritional value. Ingested caffeine is quickly absorbed in the body and peaks in 1-2 hours. Research provided by the American College of Sports Medicine (ACSM) has shown that ingestion of 3-9 mg of caffeine per kilogram (kg) of body weight one hour prior to exercise increased endurance running and cycling performance of well-trained, recreational athletes in the laboratory. This correlates to approximately 2-6 regular size cups of coffee.
Improvements have been shown in athletes that perform short-term intense (near maximal) exercise lasting approximately five minutes. The reason may be a direct effect of caffeine on muscle contraction during anaerobic exercise.
The common explanation to why endurance is improved with caffeine is that muscle glycogen is spared. Glycogen is the stored energy in the muscle tissue that is broken down during exercise. Studies suggest that glycogen sparing may occur as a result of caffeine's ability to increase fat availability for skeletal muscle use. It is important to note, however that studies cannot fully explain the ergogenic effect of caffeine.
Many of the mechanisms to explain performance improvements are unclear. There is still much research that needs to be done of the effects of caffeine on performance. There are also ethical issues in relation to sports. Caffeine ingestion currently is not illegal in sports. If an athlete deliberately takes pure caffeine to gain advantage over competitors, it is considered unethical and doping by many.
According to the ACSM, for the average, active teenager or adult who is exercising with the goals of enjoyment and self-improvement, using caffeine defeats these purposes. Although we may feel as though we are increasing our performance, it may be more related to the increase in alertness and energy due to elevated heart rates. Proper training and nutritional habits are more sensible and productive approaches. And these have clear benefits without the side effects. Always consult your medical caregiver if you have questions about your nutritional habits and the effects of caffeine on your health.
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