A Highly Effective Aid: Caffeine

Caffeine is familiar to most of us. We consume it every morning, and often throughout the day, through coffee and other drinks and foods. In sport, it is used to improve performance and is an ergogenic aid supported by substantial scientific evidence. According to legend, Kaldi, an Ethiopian goatherd in the VI or VII century, noticed that his goats jumped and danced after eating berries from a wild bush. He took the berries to a nearby monastery, where they were thrown into a fire. The aroma prompted the beans to be quickly removed, roasted, ground and dissolved in hot water, producing what is said to have been the world's first coffee. The story of Kaldi and his dancing goats is the account most frequently used to explain coffee's origin and appears to come from Antoine Faustus Nairon.

Athletes seem to have taken Kaldi's story to heart. Between 75-90% consume caffeine before or during competition. More than 100 years after the first sports study appeared, robust scientific evidence now shows that caffeine increases strength, aerobic endurance, aerobic power and muscular endurance.

“Caffeine has been legal in sport since 2004, when it was removed from the World Anti-Doping Agency's prohibited list.”

How does caffeine work? Here is a simple explanation of its mechanism of action. Your brain and other tissues have receptors for a molecule called adenosine. As the day progresses, adenosine accumulates in the brain and contributes to drowsiness. It does not only cause sleepiness: during exercise, increasing brain adenosine also contributes to fatigue. Caffeine can act centrally by blocking adenosine's binding site—it is an adenosine antagonist—increasing alertness and reducing perceived exertion during exercise. Peripherally, it may also support muscle contraction. Its role in fat mobilization and use is currently more disputed.

“Caffeine's molecular structure is similar to that of adenosine, allowing caffeine to bind to adenosine receptors, block adenosine and inhibit its effects.”

Although numerous studies and position statements show that caffeine is effective, factors such as dose, form, timing relative to exercise, training level, habitual consumption and other variables (Fig. 1) can affect how we respond.

Figure 1

Regarding quantity, an intake of 3 mg per kilogram of body weight appears effective. Doses above 6 mg per kg body weight may have unwanted effects on health and performance. This dose range—3-6 mg/kg body weight—has therefore proved effective across many sports. I recommend the minimum effective dose: 3 mg per kg body weight per day.

Timing should account for how the body metabolizes caffeine. After consumption, 95% is absorbed and metabolized in the liver by cytochrome P450 or CYP1A2, producing paraxanthine, theobromine and theophylline. Its half-life is four to six hours, although oral contraceptive use, smoking, high caffeine intake, dietary components and genetics all affect this. Peak blood concentration occurs after approximately 45-60 minutes, so it should be taken 45-60 minutes before exercise begins. This is not the only useful timing: caffeine can also be consumed during exercise or even near the end, when accumulated fatigue may be greater.

Caffeine comes from different sources, including coffee, cocoa, tea, energy drinks, chewing gum, pre-workout supplements and certain medicines. The source affects the response. Coffee, an important caffeine source, can have a performance effect similar to anhydrous caffeine, but it is extremely difficult to know how much caffeine a coffee contains. Bean type and preparation method both matter. A 2003 study found that 500 ml servings made from the same coffee at the same location on six different days varied in caffeine content by up to 59%. Bean type, the plant's geographical location and preparation technique all influence content. Some supplement studies have also found large caffeine variations and differences from label claims, which can be problematic in either direction. Caffeinated chewing gum offers an interesting form: caffeine reaches the blood more quickly, within 15-20 minutes, possibly because it is absorbed in the mouth. This delivery may be useful at specific points during competition or when caffeine absorption may be lower, as during endurance exercise when blood flow to the viscera decreases.

Regarding time of day, some studies suggest that morning intake has a greater effect on performance than afternoon intake. It is also important to remember that afternoon consumption can interfere with sleep in caffeine-sensitive people.

Whether caffeine tolerance develops has traditionally been debated in the scientific community. A study by Beatriz Lara from Dr. Juan del Coso's research group observed a degree of tolerance after four days of caffeine intake at 3 mg per kg compared with placebo. Several theories currently seek to explain the physiological basis of tolerance, but researchers do not all agree. In my opinion, it would be prudent to periodize caffeine intake to make the most of its effects. Supplement periodization will be covered in a separate article.

Finally, sex does not appear to modify caffeine's ergogenic potential: results seem similar in men and women. Oral contraceptive use may, however, double caffeine's half-life.

Remember a key rule of supplementation: more is not better and may even be worse. High caffeine intake—or even moderate intake in someone sensitive—can cause tachycardia, palpitations, anxiety, headaches, insomnia and sleep disruption. Caution is also needed in skill-based sports such as archery, where excitation or nervousness can be harmful. If coffee is withdrawn, symptoms such as headaches or irritability may occur. Do not decide to stop immediately before a competition in an attempt to maximize the supplement's effect.

“A recent review of blood-caffeine levels in fatal overdoses found an average post-mortem blood level of 180 mg per liter, corresponding to an estimated intake of 8,8 g of caffeine. Poisoning from traditional sources such as coffee and tea is rare because a very large amount—75 to 100 standard cups of coffee—would need to be consumed over a short period for the dose to be fatal. Caffeine-related deaths have generally involved very high doses from tablets or powdered or liquid supplements, mainly among athletes or patients with psychiatric disorders.”

A future post will discuss individual responses and whether genes affect them. For now, remember that periodizing caffeine can be very helpful for improving performance.

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For More Information

• Cappelletti S, et al. 2018 Nutrients; 10(5):611.
• Martins GL, et al. 2020 Front. Sports Act. Living 2:574854
• Maughan RJ, et al. Br J Sports Med 2018;52:439–455.
• Pickering C and J. Grgic / Nutrition 82 (2021) 111046
• Van Dam RM et al. N Engl J Med 2020; 383:369-378