Caffeine consumption in sport
Caffeine can help you feel alert and reduce feelings of fatigue and for most of us it is a regular part of our daily diets. It is naturally found in more than 60 plants species, the most commonly used being coffee beans, tea leaves and kola nuts. These are processed into what we all consume – coffee, tea, chocolate and soft drinks. However, the caffeine content in all of these hugely vary.
In a healthy person, if consumed in low to moderate amounts, there are minimal health consequences to its consumption and only those sensitive to caffeine suffer short-term side effects such as insomnia, headaches or nausea. Although the current recommendation is no more than 400mg (approximately five cups of coffee) per day, and even less in pregnancy, it must be noted that tolerance levels of the stimulant widely differ between individuals.
Caffeine is known for its ergogenic effects on performance and, as a result, is used by many athletes in sport. In a competition, although it is acceptable in moderate amounts, urinary concentrations over 12µg/ml (equivalent of approximately six cups of strong coffee) after competition is considered illegal and hence remains a restricted drug by the International Olympic Committee (IOC). It can safely be said, however, that an athlete would have to consume a vast amount of caffeine before reaching their legal limit and therefore it is virtually unknown for an athlete being banned due to high levels of urinary caffeine.
On consumption, caffeine is rapidly absorbed through the gastrointestinal tract, circulated to the tissues and metabolised in the liver – it is also rapidly absorbed into the brain. Elevated levels can appear in the bloodstream within 15-45 minutes of consumption and peak levels can be seen after one hour.
Scientific research looking into caffeine’s physiological effects on sub-maximal, prolonged exercise is extensive. One of the earliest studies showed that after 330mg ingestion of caffeine consumed 60 minutes prior to exercise trained cyclists increased their time to exhaustion at 80% VO2 max from 75 minutes (placebo) to 96 minutes (caffeine) [Costill et al 1978].
However, benefits are not just seen with endurance exercise. Improvements have also been seen in short-term exercise lasting five minutes at 90-100% maximal oxygen uptake. Numerous studies over the years have suggested that caffeine ingested an hour before exercise can improve performance. It must be noted, however, that some individuals will respond better to caffeine than others.
Multiple mechanisms to how such improvements are seen have been suggested. The most cited theory suggests that caffeine improves performance in early exercise as a result of enhanced fat oxidation having a sparing effect on muscle glycogen resulting in an increase in time to exhaustion. However, evidence for this is limited and alteration in muscle metabolism alone cannot fully explain the beneficial effect of caffeine on exercise.
Other theories have been suggested, such as a direct effect on the nervous system affecting perception levels and also potential direct effects on the skeletal muscle.
Nevertheless, as with any research, due to varying experimental designs and methods, there are still areas of conflict and the exact mechanisms to its success are still unclear.
"Twenty minutes before a race I'll normally drink some coffee to wake me up – if nothing happens – I have another shot. As I walk on to the stadium track I feel this massive caffeine high come on!" - Mo Farah
Various studies have set out to identify the levels of caffeine needed to improve performance. Most trained individuals seem to benefit from a moderate dose of five milligrams per kilogram of bodyweight (mg/kg), but intakes as low as 2-3 mg/kg have been found to enhance performance.
For a person weighing 70kg this would be an intake of 140- 350mg of caffeine before exercise to see potential improvements in performance. In real terms, this would be approximately 1-3 cups of 250ml fresh filter coffee. With these levels, it makes it easy for an athlete to benefit from caffeine without crossing the legal barrier.
Most of these studies focus on caffeine, but does coffee in itself have the same effect? A recent study looked at the effects of caffeine and coffee on trained cyclists performing a 45-minute time trial [Hodgson et al 2013]. One hour prior to exercise, the athletes consumed a drink containing either: caffeine (5mg/ kg), instant coffee (5mg/kg), instant decaf coffee or placebo. The main outcome was that both the caffeine and coffee time-trial times were significantly faster compared to the decaf and placebo.
The findings in this study are in line with other studies and reliably demonstrate that coffee is not inferior to caffeine in improving endurance performance. It must be considered, however, that caffeine content of coffee can vary hugely through strength and amount consumed (espresso can vary from 30-200mg caffeine per 30ml), therefore it may be harder for the athlete to know how much they were having due to the unknown and variable levels in a drink.
One of the most encouraging stories over the last few years though has been Mo Farah’s indulgence in caffeine before his Olympic 10,000m victory in London 2012. In his book Twin Ambitions , Farah writes: “Twenty minutes before a race I’ll normally drink some coffee to wake me up.” However, in the capital he has his normal espresso and as he says … “nothing happens – so I have another shot. As I walk on to the stadium track I feel this massive caffeine high come on!” The rest is history.
A common misconception is that if you choose to drink coffee or tea before exercise it will contribute to dehydration. In fact, a cup of coffee can count towards your daily fluid intake. A study performed this year proved there was no evidence of dehydration with a moderate daily coffee intake [Killer at al 2014].
The effects of coffee consumption (4x200 ml of coffee containing 4mg/kg caffeine) versus water were compared on 50 males. No differences were observed in the blood and urinary markers used to measure hydration levels, indicating that, if consumed in moderation, caffeine does provide similar hydrating qualities to water.
References available upon request.
» If consumed in moderation, coffee can be part of a healthy lifestyle and balanced diet
» Tolerance levels of the stimulant vary widely between individuals
» Caffeine has been found to increase endurance performance if taken an hour before the start of exercise
» In trained individuals, consumption of 2-5mg/kg have been found to be most beneficial, but consuming more than that has not been found to further improve performance. These doses are well below the IOC-permitted limit
» Coffee has been as effective as caffeine in improving performance though levels vary widely between drinks
» Caffeine in moderation does not affect hydration. It can count towards your daily fluid requirement
» No amount of caffeine will compensate for an unbalanced diet. If you are using caffeine to boost performance, make sure you are also fuelling adequately with a good diet.
» Alexandra Cook BSc P.g. Dip RD is a sports dietitian and a club runner with Thames Hare & Hounds. Alexandra Nutrition is a private clinical & sports dietetic consultancy covering Lincolnshire, Rutland and Leicestershire www.thesportsdietitian.co.uk
