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People have enjoyed food and drinks containing caffeine for thousands of years. As long ago as 2737 BC, the Chinese Emperor Shen Nung discovered a delicious smelling drink when the leaves from a nearby tree fell into a pot of water he was boiling.

What is caffeine?

Caffeine is a drug found naturally in the seeds, fruits and leaves of at least 63 different plants throughout the world. Although teenagers get most of their caffeine from soft drinks such as cola, it's also found in coffee, tea, energy drinks, chocolate, coffee ice cream, frozen yogurt, some nuts as well as some medicines such as cold and flu pills.

What does caffeine do?

Caffeine does a number of things to your body: small amounts can help to wake up your brain so that you feel more alert; it increases the amount of a brain chemical that helps improve your mood; and it releases some nutrients which provide us with more energy.

That's the good news. The bad news comes  when we overindulge in  caffeine.

Studies have found that too much caffeine can make us feel  irritable and nervous.

It can also cause headaches, diarrhoea, an increase in blood pressure and heart rate, and difficulty sleeping and concentrating.

Caffeine speeds up the loss of calcium from our body - and most of us already don't eat enough of this mineral, which is important for building  strong bones and teeth.

Caffeine makes us pass more water through urinating, which may cause dehydration in hot weather because water is also lost through sweat. So, it is best not to have too much caffeine when the weather is hot.

How much caffeine should you have?

For teenagers, doctors recommend no more than 100 milligrams of caffeine a day, that is, a small cup of coffee or 2 cans of cola a day.

Most of us don't realise how much caffeine we're ingesting each day. You'll be surprised at the caffeine content of some of the following foods:

If you think your caffeine intake is too high, try to cut down the amount slowly by drinking one less can of cola or a smaller cup of coffee each day. This will help your body get used to the smaller amounts of caffeine gradually, otherwise you may get headaches, feel muscle pain and be depressed.



The buzz on caffeine