A question posed to me frequently is whether
caffeine is bad for health or a useful and safe aid to exercise? And this article will attempt to discuss this question.
The use of caffeine in sport is topical and over the past 2-3 years there have been a large number of well designed studies examining its use. These have been consolidated into the excellent report in 2003 By Dr Briony Thomas entitled Caffeine and Health: A Review. Despite this review being commission by PG Tips tea (a tea producing subsidiary of Unliver Bestfoods Ltd in the UK), it is both unbiased and informative.
Caffeine has mixed reviews in health and sport, so, if I were to conclude this article now, I would say treat caffeine like everything, i.e. moderation is the key. However, I will attempt to summarise the benefits and negative effects and discuss using it to your advantage, so you can use this information to make up your own mind.
Caffeine as a Drug
Strictly speaking caffeine is classed as a 'drug' though, due to it's prevalence in a number of commonly-consumed foods it is sometimes thought of as a 'nutrient'. The negative effects of caffeine include its links with raised blood pressure, increased heart rate, arrhythmias, dehydration, anxiety, insomnia, headaches, heartburn, osteoporosis, birth defects, digestive ulcers, miscarriage, infertility, cancer, cardiovascular disease, and more. Please be aware however that these needn't be true, it's just that they are reported.
Reported positive effects of caffeine are relief of fatigue, improve alertness and mental efficiency, creativity and improved athletic performance.
Sources of Caffeine
Caffeine, in its chemical form, i.e. 1,3,7-trimethylxanthine is found in many plants, especially so in tea and mate leaves, coffee and cocoa beans, cola nuts and guarana seeds. It is therefore a natural constituent on many beverages and foods linked to the above, but is also added to other products either for flavouring purposes or for its stimulant effects.
The main sources in the Western diet are coffee, tea, colas and other soft drinks, cocoa, stimulant or energy drinks, chocolate and coffee/chocolate flavoured desserts. It is also used pharmaceutically in prescription and over-the-counter medicines either for its direct action or to reduce drowsy effects of the medicine it's associated with. Examples of these are cold and flu remedies, pain killers, anti-histamines, diuretics and weight loss aids.
In the bodybuilding and sports, many people also use caffeine pills to enhance performance, these are typically 50-200mg each, and doses may be as much as 300-400mg.
Guide to Caffeine Contents
The following table indicates average amounts of caffeine in commonly consumed products (MAFF 1998; Thomas 2003).
| Product | Caffeine Content |
| Cup of tea (150ml) | 35mg |
| Mug of tea (250ml) | 50mg |
| Cup of instant coffee (150ml) | 75mg |
| Mug of instant coffee (250ml) | 100mg |
| Cup of brewed coffee (150ml) | 100mg |
| Mug of green tea (250ml) | 20mg |
| Can of cola (330ml) | 30mg |
| Can of stimulant drink | 80mg |
| Serving of coffee/chocolate dessert | 30mg |
| Bar of chocolate | 15mg |
| Hot chocolate/cocoa | 4mg |
Whilst the above table show averages there may be huge variation especially in tea and coffee which are consumed 'weak' or 'strong' and there is a large number of variety and blends. It is also common for a cup of tea not to be completely consumed. Stavric et al (1988) demonstrated that there is significant error when trying to estimate actual caffeine content of tea and coffee.
It is not easy for consumers to determine how much caffeine they are consuming as the presence of naturally occurring caffeine will not be declared on a product label, nor, under current legislation, does caffeine added for flavouring purposes only have to be mentioned by name. However, in the UK as from July 1st 2004, this will change, and products containing more than 150mg caffeine per litre (or per kg) must be labelled 'high caffeine content' and the amount declared in mg/100ml or mg/100mg.
Caffeine Intakes
Average caffeine consumption around the world is 76mg/person/day with huge variations between countries (Barone and Roberts 1996; Fredholm et al 1999; Strain et al 1994):
- Scandinavia: over 400mg/person/day
- North America: 240-360mg/person/day
- UK: 280mg/person/day (a significant number of heavy consumers consume as much as 525mg daily)
In the USA coffee is the main contributor to intake, whereas in the UK, unsurprisingly tea consumption is much larger. Since the above studies it is estimated that average caffeine intakes have risen especially from the increased consumption of stimulant drinks.
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