Caffeine: Overview

As well as having negative effects, caffeine does possess some positive attributes.

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Present knowledge indicates that moderate intakes of caffeine should not be harmful to most people, and that caffeine may even have positive effects in preventing some diseases.  As is so often the case, moderation in caffeine consumption seems to be the sensible path to follow.


The amount of caffeine in some common foods and beverages is as follows:

Caffeine content of...Serving Sizemg
Coffee, brewed1 cup40-180
Coffee, instant1 cup30-120
Coffee, decaffeinated1 cup3-5
Tea, brewed American1 cup20-90
Tea, brewed imported1 cup25-110
Tea, instant1 cup28
Tea, iced12oz can22-36
Soft drinks, caffeinated12oz can36-90
Soft drinks, decaffeinated12oz can0
Cocoa1 cup4
Chocolate, milk1 ounce3-6
Chocolate, bittersweet1 ounce25

Why it is Recommended

Research indicates that caffeine intake can reduce the risk of developing Parkinson's disease and possibly also liver cancer.  There are indications that caffeine may decrease liver damage.

Another positive effect is that caffeine can increase the resting metabolic rate in lean and obese people, which is why it is often included in slimming pills and products, including herbal diet pills.  There are many studies that document the slimming effects of caffeine.  Unfortunately, most of these studies used slimming mixtures that contained caffeine in combination with compounds such as ephedrine or green tea extract.  This makes it difficult to judge how much of the observed weight loss was due to caffeine and how much was due to one of the other ingredients.  Some researchers do maintain that "high caffeine intake was associated with thermogenesis and fat oxidation and with suppressed leptin in women." [Westerterp-Platenga & coworkers, 2005]

150mg of caffeine a day may promote slimming: Do not increase coffee and/or tea intake to absurd levels such as 10 cups per day to promote weight loss.  Excessive caffeine intake may cause pronounced side-effects like palpitations, insomnia, irritability etc.

Drink tea or coffee in moderate quantities when you are trying to lose weight, but keep in mind that you also need to reduce your energy intake with a sensible, balanced, low-energy diet, and increase your energy output by doing daily exercise for at least 30 minutes or more per day.

Research indicates that intakes of caffeine exceeding 9mg/kg of body weight (e.g. a 70kg athlete ingesting more than 630mg of caffeine per day) do not increase athletic performance more than having about 6mg/kg of body weight (e.g. the 70kg athlete would only have to ingest 420mg of caffeine per day).  The optimal dose for improving athletic performance according to Burke and Deakin (2000) is, therefore, 5-6mg per kg body weight.  Too high a caffeine intake by sportsmen and women can cause negative side-effects such as the shakes, palpitations, headaches etc.  It may also cause dehydration.  Furthermore, it has been found that some athletes do not respond to caffeine stimulation by increasing their performance, so you need to experiment before a big event to see if caffeine supplementation does improve your performance or not.

Caffeine is known to enhance athletic performance, reduce fatigue and improve recovery in athletes.  The following physiological effects of caffeine may enhance athletic performance:

  • stimulation of the central nervous system, which leads to reduced perception of effort (reduced fatigue), or enhanced use of muscles
  • stimulation of the heart muscle
  • stimulation of diuresis (excretion of water by the kidneys)
  • stimulation of the release of epinephrine by the body (the "fight-or-flight" hormone), which releases fats for muscle activity.

In view of the above, caffeine has been used for many years by sportsmen and women to enhance their performance, prevent fatigue and give athletes a "lift".

Because of its stimulant properties, caffeine can also help people stay awake and be more alert in situations where they are required to concentrate.


Experts agree that moderate intakes of caffeine should not be harmful to the general population.

The UK Food Standards Agency has, for example, recommended that the general population and pregnant women should not have more than 300mg of caffeine per day (e.g. four cups of instant coffee or six cups of regular tea).

When calculating daily caffeine intake, remember to include caffeine arising from any medications you may be taking: having three headache pills would contribute 150mg of caffeine to your intake.

Counter-Indicators and Warnings

Caffeine stimulates diuresis or excretion of water by the kidneys, leading possibly to dehydration.  Intake of caffeine should therefore be balanced by good hydration.

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