Caffeine’s use in sport is well established due to its performance enhancing benefits. Athletes consume caffeine in many different forms such as sports drinks, gels, gum and tablets.
Dr Sarah Brewer says: 'Caffeine interacts with brain chemicals to increase alertness and decrease the perception of effort and fatigue. Too high a dose can cause other stimulant effects, however, such as increasing the heart rate. Regular intakes of above 400mg per day can also lead to withdrawal symptoms such as headache and fatigue, so it’s important not to over-indulge.’
What does caffeine do?
Caffeine is a stimulant ‘enabler’ that blocks adenosine receptors in the brain. Adenosine acts as a brake which causes the brain to slow, and by blocking this action caffeine increases alertness and reduces the perception of effort.
Caffeine also has effects on fat metabolism, helping to release fat into the circulation to act as a fuel during strenuous exercise and preserving higher levels of carbohydrate stores (glycogen) in the muscles and liver.
Caffeine can enhance performance in both recreational and elite athletes. By reducing the perception of exertion, it doesn’t feel like you are working as hard as you are, cognitive functions are enhanced which in turn aids decision making, increased energy levels and reduced fatigue.
Studies show that caffeine ingestion can improve strength and power performance in female team-sport players (i), reduce perceived exertion and fatigue in males exercising in a hot, dry environment (ii), significantly improve exhaustion during intense cycling exercise (iii), and help relive feelings of soreness and fatigue following an endurance cycling event (iv).
Caffeinated chewing gum can also enhance cycling performance when taken immediately before cycling . Caffeine gum also reduces fatigue during repeated high-intensity sprint exercise in competitive cyclists (vi).
In fact, the performance enhancing benefits of caffeine are so well established that until recently, the International Olympic Committee banned high consumption for professional athletes. Now however, it is recognised that caffeine is regularly consumed as part of the normal diet of most athletes, and it is near impossible to distinguish between normal dietary consumption and the consumption of caffeine for deliberate performance enhancement.
Getting caffeine from your diet
Caffeine is naturally found in coffee, black and green teas, chocolate and even some herbal tea blends (check labels). Caffeine is also added to some soft drinks such as cola, and to many over-the-counter medicines designed to treat headaches and colds.
The amount of caffeine in tea and coffee varies widely, depending on how long the drink is left to brew and the size of your cup. Typical caffeine contents are as follows:
- 60ml espresso contains around 80mg caffeine
- 125ml cup of instant coffee provides 65mg caffeine
- 125ml cup of filtered coffee has 85mg caffeine
- 150ml cup of tea includes 32mg caffeine
- 250ml standard can of energy drink contains around 80mg of caffeine (check labels)
- 330ml can of cola provides around 40mg (check labels).
There’s between 25mg and 50mg caffeine in a 50g bar of dark chocolate and around 10mg caffeine in a 50g bar of milk chocolate.
Caffeine tablets should be taken approximately 30 minutes before exercise as this is the typical time they take to be absorbed by the body. Caffeine in the form of chewing gum is absorbed more quickly, and should be taken in a lower dose 10 to 15 minutes before you wish to feel the benefits.
Caffeine can stay in your system for a considerable amount of time, so avoid consumption after 6pm as this could disrupt your sleep.
Different people absorb and break down caffeine at different rates. Choosing a tablet that provides 50mg caffeine or a gum that provides 100mg caffeine enables you to tailor your intake to a level that suits you, depending on your intake of other caffeinated food and drinks.
A review by the European Food Safety Authority concluded that single doses of caffeine of up to 200mg (about 3mg per kilogram of body weight for someone weighing 70kg) are safe, and that habitual intakes of up to 400mg caffeine per day should have no consequences for healthy adults (vii). Women who are pregnant or breast-feeding should limit their intake to no more than 200mg caffeine a day.