Where does caffeine come from?
Caffeine is found naturally in coffee beans, tea leaves, chocolate, cocoa beans and kola nuts. There are 63 plant species whose leaves, seeds or fruits contain caffeine.
Coffee beans: 0.6 – 2% for arabica and 3 – 4.5% for robusta
Tea leaves: 2.2% for green tea and 4% for black tea
Cocoa beans: 0.05 – 0.30%
Guarana: 2 – 5.8%
Yerba mate: 0.3 – 2.4%
Kola nuts: 1.5 – 3%.
Performance-enhancing effect of caffeine
A precise explanation for the performance-enhancing effect of caffeine remains unknown. In all likelihood, the performance-enhancing effect of caffeine during endurance or high intensity training results from the increased ease of use of fat as a fuel for exercise while preserving the body's limited carbohydrate reserves.
However, although an improvement in endurance performance generally follows the intake of caffeine, it is important to first take into account the influence of nutrition on the variation in responses following the consumption of caffeine. Indeed, the differences in sensitivity to caffeine, tolerance and hormonal responses observed in individuals following caffeine intake in the medium and long-term require the performance-enhancing qualities of this substance to be put into perspective.
Individuals who do not normally consume caffeine may experience undesirable side effects. Caffeine stimulates the central nervous system and can cause nervousness, headaches, insomnia, irritability, palpitations, tremor, psychomotor agitation and increased heart rate and blood pressure.
In terms of thermoregulation, caffeine acts as a powerful diuretic, its use can lead to unnecessary loss of fluids before physical exertion and affect thermal regulation and athletic performance in hot conditions.
Ingestion of small amounts of caffeine can have positive effects, but consumption in excess can have serious consequences.
Caffeine and doping
The IOC allows the consumption of caffeine by athletes as long as its concentration in urine samples does not exceed 12mg/mL. Only 0.5 to 3% of caffeine ingested is found in the urine, the remainder being largely used by the liver, with relatively large differences between individuals. Athletes should be aware that 600 to 800 mg of caffeine (4-7 cups of coffee) consumed in 30 minutes significantly increases urinary caffeine concentration to a level that can cause disqualification during competitions.
It should be noted that caffeine is the only substance for which urinary limits were imposed by the IOC.
According to the World Anti-Doping Agency, caffeine is not considered as a prohibited substance. However it appears in the 2014 monitoring programem. (http://www.wada-ama.org/).