Caffeine, is it bad for health or a useful and safe aid to exercise?
Article by James Collier BSc (Hons) RNutr – Contributor in Nutrition
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, kola 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).
|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|
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.
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.
Caffeine Metabolism, Half Life and Toxicity
Caffeine is rapidly absorbed from the digestive system reaching peak concentration in blood 60-90 minutes after ingestion. Caffeine is then metabolised in the liver by the cytochrome P450 enzyme system producing a number of metabolites and some is excreted unchanged in urine. Complete clearance of caffeine from plasma and urine is not until 24-48 hours after ingestion of the last dose. The average half life of caffeine is 4-5 hours but this can vary between 2-10 hours as a result of genetic, physiological and environmental factors (FSPB 2002).
The LD50 (lethal dose for 50% of the population) of oral caffeine is estimated to be 10g, i.e. the equivalent to 50-100 cups of coffee; however this is merely an estimate (Thomas 2003). Toxic effects are abdominal pains, vomiting, seizures and reduced consciousness. Most cases of overdose are due to over consumption of pills and stimulants.
Caffeine as a Stimulant
Methylxanthines exert their effect by blocking certain adenosine receptors in the brain. Adenosine slows down brain activity by a neuronal method not entirely understood, so by blocking its uptake, caffeine acts as a stimulant. Its stimulatory effects propel directly or indirectly onto the heart, lungs, blood vessels, kidneys and muscles causing an improvement in performance and possibly strength.
Addictiveness and Tolerance of Caffeine
Caffeine is a psychoactive drug, but does it cause actual addiction illustrated by dependence? Caffeine does seem to cause tolerance as the need to increase the amount consumed to initiate stimulation is apparent. Withdrawal symptoms are also apparent in some people, including headaches and fatigue and last from two days to over a week. Whilst caffeine may exhibit some criteria for dependence, it is debatable as to whether caffeine is an addictive drug by definition. What do you feel?
Caffeine and Athletic Performance
This is the bit we’re interested in! Does caffeine help our performance in the gym and ultimately improve our gains? The short answer is yes it does, and this has been confirmed scientifically!
Caffeine has been shown to increase both short term intense exercise performance, ‘stop-start’ activities (football, rugby, etc), long distance running and help our performance in the gym, so we can train more effectively and ultimately increase size and strength. (EU SCF 2001; Kovacs et al 1998).
The mechanism of how caffeine initiates its ergogenic effect is, however, poorly understood. It is likely that it increases fat burning, thus sparing our carbohydrate stores, which in turn means that the point of lack of ready carbohydrate availability is delayed, so helps performance. This theory also acknowledges the fact that caffeine is slightly fat oxidising, therefore useful in keeping body fat off.
Caffeine may also stimulate neural signals between the brain and neuromuscular junction (how nerves cause muscles to contract) and increase production of metabolites in muscle helping contraction occur.
Caffeine was previously banned by the International Olympic Committee (IOC) pre-competition and blood levels should not have exceeded 12mcg/ml. This was in view of its ergogenic effects on performance as it was thought it gives an unfair advantage. However there was no restriction during training and no random drug testing for it. Since January 2004, though, any restriction on caffeine’s use pre-event has been lifted, even pre-event, as its use is so widespread and socially acceptable, so caffeine-containing ergogenic aids can be consumed freely during this year’s Olympic events. It should also be noted that the ergogenic benefits of caffeine occur well below the formerly restricted IOC levels (American College of Sports Medicine 1999).
Caffeine and Fluid Balance
Optimal fluid intake is the most important aspect of sports performance. Caffeine is a diuretic but there is a threshold level below which it has zero effect on fluid balance. Infact it takes as much as 250mg caffeine in a single dose (Maughan & Griffin 2001) to have any diuretic effect and even 2 cups of tea or coffee in one go will have zero effect on dehydration. The diuretic effect of caffeine is also greatly affected by habitual intake and a high degree of tolerance can be developed. Furthermore, experiments have looked at this aspect with supplemental doses of caffeine, whereas in life we consume it in drinks where the accompanying fluid will offset any dehydrating effect (Thomas 2003).
This means, that despite what you will have read on many websites and magazines tea and coffee are very useful for good hydration and there is no evidence to say that they are dehydrating. Dispel the myth that caffeinated beverages are diuretics now! Very high supplemental doses with no accompanying fluid may have a negative effect on hydration, but this effect is not as significant as you’ll have been led to believe before.
Some studies have looked at the comparison between stimulant drinks and isotonic drinks and found little difference in their rehydrating effects, and any difference was due to the osmolarity and composition in terms of carbohydrate content and electrolytes rather than caffeine content (FSPB 2002).
It is important for bodybuilders and athletes to note though that hot drinks are very poor hydrators in exercise as they are released from the stomach slowly, therefore tea and coffee should be discouraged pre-exercise as the fluid absorption will be delayed and they lie heavily on the stomach.
Caffeine does appear to have a diuretic effect in people who feel they frequently need to wee. However this is due to caffeine’s effect on smooth muscle rather than any diuretic effect, but may explain the need to wee in some people after a cup of coffee (coupled with the fact that they’ve just drank 250ml of fluid) (Arya et al 2000). Therefore people who are slightly urinary incontinent should consume less than 200mg of caffeine per day.
Caffeine as a Pill
Many sports supplement manufacturers now produce a formula containing caffeine on its own (either as the raw compound or as guarana) or in combination with other ingredients in their product range. It is sold as a stimulatory aid or as a thermogenic aid for weight loss, and amounts typically range from 50-200mg per tablet/capsule. If people do choose to use these then caution should be taken especially if caffeine-containing beverages are consumed simultaneously so that they do not become too ‘hyped-up’ or, if high dose pills are taken, then there may be a diuretic effect, especially as they are consuming caffeine with no fluid (as opposed to tea/coffee made with water).
Caffeine is often included in many thermogenic weight loss and stimulant formulas, the most popular being the ECA stack (ephedra-caffeine-aspirin stack), which is commonly used in bodybuilding, fitness and weight loss due to the synergistic action of the three substances. ECA can be sold as a legal supplement or as an illegal performance enhancer, though the effects are the same. Ephedra is the herbal form of the drug ephedrine from the ma huang plant. The three compounds work synergistically for maximum effect and levels are typically 350mg ephedra/ma huang (which is 6% ephedrine), 200mg caffeine and 300mg aspirin. Formulas are not always sold as the ECA stack and ingredients may be labelled as ma huang for ephedra, guarana for caffeine and white willow bark for aspirin. Although laws are tightening up for this supplement in some countries, there are many formulas which remain very popular.
Relationships between Caffeine and Disease
The link between caffeine consumption and osteoporosis (brittle bone disease) has been debated for years due to it’s effect on urinary calcium excretion. However this effect is minor and at normal intake levels, providing that a good calcium intake is consumed, there is no significant risk of women developing osteoporosis later in life (Heaney 2002).
The link between caffeine and cardiovascular disease (CVD) is unclear, ranging from increasing to reducing risk. The problem is studies have been performed looking at tea/coffee consumption rather than caffeine intake specifically, and tea is high in flavanoid antioxidants. It should also be noted that caffeine consumption is often associated with CVD risk factors like smoking, alcohol consumption and physical inactivity. Looking at overall risk of heart disease and stroke there appears to be no good relationship (Thomas 2003). Short term intake of caffeine does increase blood pressure, however as these effects disappear after 3 hours there appears to be no long term effects, especially as people develop tolerance (Nurminen et al 1999). There is no evidence that caffeine has any effect on blood cholesterol and other lipid levels.
There is reasonable evidence that coffee consumption could protect against incidence of Parkinson’s disease (PD) (Ross et al 2000), probably due to effects on dopamine levels.
Caffeine in Health and as an Ergogenic Aid
An intake of caffeine in adults of 300-400mg/day poses no public health hazard, and may even have some benefits to bodybuilders and athletes and possibly health as a whole (Thomas 2003). There is little evidence that intakes of 500-600mg/day have any adverse effects at all. This means in practice we can safely enjoy 4-5 decent cups of tea or coffee per day with no adverse effects in any respect. Stimulant drinks may also be useful if used occasionally and sensibly, for example if you’re feeling very lethargic and need a pick-me-up before training. Caution should be taken if you choose to use caffeine pill supplements, especially if it is part of a formula with other compounds such as popular pre-workout supplements etc.
As caffeine has been consumed for hundreds of years and has health benefits it could be viewed as a non-essential nutrient. Its effect as a stimulant, if used correctly is useful to fuel intense workouts. However, do not consume tea or coffee before a workout as hot beverages make you feel bloated and restrict hydration.
- American Collage of Sports Medicine (1999). Caffeine and exercise performance
- Arya LA, et al (2000). Dietary caffeine intake and the risk for detrusor instability: a case controlled study. Obs and Gyne 96(1): 85-89
- Barone JJ, Roberts HR (1996). Caffeine consumption. Food Chem Tox 34: 119-229Fredholm BB, et al (1999). Actions of caffeine in the brain with special reference to factors that contribute to its widespread use. Pharmacol Rev 51: 83-133
- EU SCF (2001). Report of the Scientific Committee on Food on composition and specification of food components intended to meet the expenditure of intense muscular effort, especially for sportsmen (Section 10.1 Caffeine). SCF/CS/NUT/SPORT/5
- FSPB Stimulant Drinks Committee (2002). A Review of the Effects of Stimulant Drinks. FSPB
- Heaney RP (2002). Effects of caffeine on bone and the calcium economy. Food Chem Tox 40: 1263-1270
- Kovacs EMR, et al (1998). Effect of caffeinated drinks on substrate metabolism, caffeine excretion and performance. J Appl Physio 85: 709-715
- MAFF (1998). Food Safety Directorate. Survey of caffeine and other methylxanthines in energy drinks and other caffeine-containing products. Food Surveillance Information Sheet 144
- Maughan R, Griffin J (2001). Tea drinking and fluid balance. Crawley: Brooke Bond tea Company
- Nurminen M-L, et al (1999). Coffee, caffeine and blood pressure: a critical review. Euro J of Clin Nutr 53: 831-839
- Ross G, et al (2000). Association of coffee and caffeine intake with the risk of Parkinsons disease. J Am Med Assoc 283(20): 2674-2679
- Stavric B, et al (1988).Variability in caffeine consumption from coffee and tea: possible significance for epidemiological studies. Food Chem Tox 26(2): 111-118
- Strain EC, et al (1994). Caffeine dependence syndrome: evidence from case histories and experimental evaluations. J Am Med Assoc 272: 1043-1048
- Thomas B (2003). Caffeine and Health: A Review. Unilever Bestfoods Ltd
Acknowledgments: Thanks to member Hulkster for his information on his research on caffeine and performance