What is Caffeine?Caffeine is a substance from the methylxanthine family that occurs naturally in the leaves, nuts and seeds of approximately 60 different plants. It enjoys social acceptance and widespread use around the world. Traditionally the dietary sources of caffeine have been tea, coffee, chocolate and cola drinks. These beverages typically provide 30-120 mg of caffeine per serve but may vary considerably particularly within coffee based drinks (see table 1). The introduction of caffeine (or guarana) to ‘energy drinks’, confectionery and sports foods/supplements within the past 10 years has increased the opportunities for athletes to consume caffeine, either as part of their everyday diet or for specific use as an ergogenic aid. Some non-prescriptive medications also contain 100 -200 mg of caffeine per tablet. (See table 1)
table 1: Caffeine Content of Common foods and Drinks
GU (Plain Orange, Vanilla, Chocolate and
Triberry) sports gelsGU (Blackberry and Espresso) sports gels 32 g sachet
* The caffeine content of hot tea, coffee and iced coffee varies
investigate performance effects in elite athletes under field
widely, depending on the brand, the way that the individual makes
conditions or during real-life sports events using caffeine from
their beverage, and the size of their mug or cup. Espresso samples
common food sources are scarce. This is important to remember
have been reported as they represent the likely caffeine content
as caffeine sourced in the general population may vary both in
for most beverages prepared in store. It should be noted that some
terms of the amount of ingested and other included ingredients.
retailers sell special brews that come in extra large containers with extra strong varieties of coffee. Some of these brews can provide
Traditional protocols for the use of caffeine involved the intake of
500-1000 mg of caffeine per serve.
caffeine one hour prior to the event, in doses equivalent to ~6 mg/
+ does not include McCafe outlets.
kg (e.g. 300-500 mg for a typical athlete). More recently, evidence from studies involving prolonged exercise lasting 60 minutes or
longer, suggest beneficial effects from caffeine intake occur at
In 2004 caffeine was withdrawn from the World Anti-Doping
small-moderate levels of intake (1-3 mg/kg BM or 70-200 mg
Agency Prohibited List, allowing athletes who compete in sports
caffeine), when caffeine is taken at a variety of times (before and/
that are compliant with the WADA code to consume caffeine,
or throughout exercise, or towards the end of exercise when the
within their usual diets without fear of sanctions.
Caffeine has numerous actions on different body tissues. The
A period of caffeine withdrawal does not appear to influence
actions may vary between individuals and include both positive
the performance enhancing effects of caffeine on endurance
and negative responses. Early scientific studies suggested that
exercise tasks. Furthermore, there is no evidence of a dose-
caffeine could improve endurance exercise performance by
response relationship to caffeine - that is, performance benefits
increasing the mobilisation of fats from adipose tissue and the
do not seem to increase with increases in the caffeine dose. It
muscle cell and ‘sparing’ muscle glycogen. Follow-up studies
is therefore advisable that athletes use lower caffeine doses to
now show that the effect of caffeine on muscle glycogen during
both maximise performance potential whilst minimising possible
sub-maximal exercise is short-lived and inconsistent. That is, not
all athletes respond in this way. Therefore, it is unlikely to explain the enhancement of exercise capacity and performance seen in
prolonged continuous events and exercise protocols.
The mechanism underpinning performance benefits remain
Sound evidence exists that caffeine enhances endurance and
unclear, but the most popular current theory involves caffeine
provides a small but worthwhile enhancement of performance
capacity to bind to adenosine receptors which are located
over a range of exercise protocols. These include short duration
throughout the body. Adenosine receptors help regulate many
high intensity events (1-5 min), prolonged high intensity events
physiological, neurological and immunological processes which
(20-60 min), endurance events (90 min + continuous exercise),
may lead to alterations to the perception of effort or fatigue,
ultra-endurance events (4 hours +), and prolonged intermittent
as well as direct effects on the circulatory system and skeletal
high intensity protocols (team and racquet sports). The effect on
muscle. There are ~100 studies in the scientific literature looking
strength/power and brief sprints (10-20 sec) is unclear.
at caffeine and performance various forms of exercise.
Some individuals may benefit from caffeine when used during
prolonged endurance or intermittent sports, including team
Caffeine is rapidly absorbed by most individuals. Peak blood
sports, as a training aid or competition aid, and prior to high-
caffeine levels occur usually 45-90 mins following ingestion (but
intensity events, as a training aid or competition aid.
can take as long as 3hrs). The half-life of caffeine (an indication of its duration of action) is approximately 6-7hrs. Caffeine can also be readily absorbed in the mouth in the case of caffeine containing chewing gums etc. Most studies of caffeine and performance have been undertaken in laboratories using purified forms of caffeine. Studies that
are there any siDe effeCts?Although evidence of specific health problems is equivocal, long-term intake of large amounts of caffeine (>500 mg per day) are generally discouraged by health authorities. We are aware that current caffeine intake practices of athletes are often ad hoc and unsystematic. Combined with the large variances in caffeine from coffee based beverages there is potential for side-effects or negative outcomes from caffeine use.
Short-term increases in caffeine intake can cause a mild increase in urine production at rest but caffeine-containing drinks are unlikely to cause an exercising individual to become dehydrated. Habitual caffeine consumption does not cause any sustained alteration in fluid balance. Moreover, caffeine-containing drinks such as tea and coffee may provide a significant source of fluid in the everyday diets of many people. In fact, restricting intakes of these beverages due to concerns over caffeine induced urine losses is likely to have a far greater negative impact on fluid balance. At higher levels of intake, caffeine has the potential to cause increases in heart rate, impairments or alterations of fine motor control and technique, and over-arousal (interfering with recovery and sleep patterns). Impairment of technique may affect the performance of a number of sports, and over-arousal may interfere with the ability to recover between training sessions, or multi-day competitions. These concerns add to the importance of finding the lowest effective dose of caffeine that can be used to achieve a performance enhancement. There may be interactions between caffeine and other supplements/nutrients used by athletes (e.g. bicarbonate, creatine) that need to be explored in terms of performance outcomes and potential side-effects. The use of caffeine by children and adolescents participating in sport is not advised, particularly in hot environments.
June 2011 This is a sports nutrition publication of Sports Dietitians Australia.
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