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Caffeine is found in the leaves, seeds and fruits of over 60 plants worldwide. Caffeine naturally occurs in tea, coffee and chocolate. It is added to ‘kola’ type soft drinks and energy drinks.

What does caffeine do?

Caffeine has a stimulant effect, through your nervous system. This can help the brain to produce faster and clearer thoughts, take away feelings of tiredness and improve exercise performance.

Too much caffeine can cause irritability, anxiety, an increase in heart rate and insomnia. It all depends on the rate that your body metabolises caffeine and how much caffeine you usually have (as our bodies can acquire a tolerance to the effects of caffeine). Quick metabolisers can have a cup of coffee just before bed and still sleep, while slow metabolisers eliminate the caffeine more slowly and can feel the effects many hours afterwards.

Often you may hear that caffeine has a diuretic effect (increases the rate of urination): this is true, but in a cup of tea, coffee or cola drink there is plenty of fluid to offset these losses.

How much caffeine should we have?

There are no firm recommendations on the amount of caffeine we should consume, so we should be aiming for moderation, say 300-400mg or 3 cups of coffee each day.

  • Pregnant women are advised to limit the amount of caffeine they consume each day to around 2 cups of coffee (<200mg caffeine), as pregnancy slows down the rate that caffeine is metabolised. High caffeine levels have been linked to low birth weight and reduced fertility in women trying to conceive,
  • Children do not need to include caffeine in their diet. Caffeine in children has been linked to irritability, sleep problems, aggressive behaviour and attention and conduct problems.
  • Breastfeeding women should be aware that caffeine may have a stimulating affect on their baby.
  • Caffeine is present in many more products these days, particularly energy drinks. These drinks contain more added sugar than is recommended and so it is best if these drinks are avoided, particularly for children and pregnant women as we don’t know the effects of early exposure to caffeine.  

How much caffeine is in food and drinks?


Average Caffeine Content (mg)

Energy shots


Energy drinks (250 ml can)


Brewed/Espresso Coffee (1 cup)*


Instant Coffee (1 cup)


Tea (1 cup)


Cola drinks (375ml can)


Chocolate bar (50g)


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