A: Caffeine is the most commonly consumed over-the-counter drug. In the United States the average amount of caffeine consumed per day is about 200 mg, or 2 cups of coffee. Additionally, more than 10% of the population consume greater than 1000 mg per day. Caffeine (Table 1) is naturally present in many foods (i.e. coffee, teas, sodas, and chocolate), but is also found in non-prescription medications and in certain prepared foods (i.e. energy bars and gels). Caffeine is a drug with no nutritional value and is absorbed quickly peaking in the blood by about 1-2 hour. As an ergogenic agent, caffeine has been shown to enhance performance in both short-term and endurance exercise performance.
| Table 1. Sources in Common Beverages and Foods**: |
| Source |
Serving Size |
mg/Serving Size |
| coffee, drip |
5 ounces |
106 - 164 |
| coffee, instant |
5 ounces |
47 – 68 |
| tea (black) brewed |
5 ounces |
20 - 80 |
| Iced tea |
6 ounces |
67 - 76 |
| hot chocolate, mix |
12 ounces |
2 – 8 |
| Cola Beverages |
6 ounces |
36 - 57 |
| milk chocolate |
1 ounces |
6 |
Effect on Performance: Laboratory research suggests that consuming 3-9 mg/kg (e.g. 2-6 cups of coffee or 200-1000 mg) of caffeine before increases both short-term and endurance exercise performance. Despite a limited number of controlled studies, sprint performance does not appear to be affected by caffeine. The mechanism by which caffeine exerts its positive benefits is not fully understood, some suggest that it may be related to sparing of muscle glycogen or the effects on lactate utilization. Because caffeine is an ergogenic aide the International Olympic Committee (IOC) and the National Collegiate Athletic Association (NCAA) have determined that acceptable limits of urinary caffeine are <12 mg/ml and <15 mg/ml, respectively. For example, a 70 kg male that consumes 5-6 cups of coffee (~9 mg/kg caffeine) would be expected to have less than 12 mg of caffeine per ml of urine at about one hour after consumption.
Adverse effects: Commonly reported side effects include jumpiness, anxiety, insomnia, and irritability. Some have reported a risk of heart arrhythmias and hallucinations with high doses. Although, ingestion of caffeine can produce a mild urinary excretion of water it is unlikely to negatively influence hydration status during exercise. Long-term consumption of caffeine is not associated with adverse health effects and more recent studies suggest there may be positive health benefits, such as reduced risk of certain cancers and may reduce the risk of developing gallstones. However, it should be noted that caffeine is addictive. Moreover, tolerance has been reported to increased amounts of caffeine. Frequently reported symptoms during caffeine withdrawal include headaches, mood changes, fatigue. Symptoms from withdrawal peak within 24-48 hours and can last up to one week.
References and Web Resources:
Graham, TE. Caffeine and exercise, metabolism, endurance and performance. Sports Medicine (2001): 31 (11):785-807.
Spriet, LL and Graham, TE. Caffeine and Exercise, Current Comment from the American College of Sports Medicine, July 1999.
**Caffeine Content of Beverages, Foods and Drugs
Information taken from research conducted by The U.S. Department of Nutritional Services (All figures approximate): http://www.holymtn.com/tea/caffeine_content.htm
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