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Caffeine

• Caffeine is readily absorbed and peak concentrations occur 30-60 minutes in young adults after ingesting it. High doses slow the metabolism down and can remain in the brain for 9-15 hours.

• Percolated coffee usually contains more caffeine than instant. If the coffee grounds are boiled during preparation, as is common in Scandinavian countries, the caffeine content can be as high as 500mg per cup.

• Tea brewed directly from crushed leaves has more caffeine than tea produced with a tea bag.

• Plain chocolate contains more caffeine than milk chocolate.

Caffeine enters the bloodstream very quickly and can take between three and seven hours to leave the body. Its effects on people can be variable – some people regularly drink caffeine-laden drinks at night-time with no ill-effects; others cannot even drink one cup in the morning without it affecting them at night. Scientists believe this may be because caffeine-sensitive individuals metabolize the substance more slowly (see opposite, for factors involved in metabolizing caffeine).

Research shows that if you are not a habitual coffee drinker, the effects will be greater; and that caffeine metabolism varies with age (children, for example, tend to metabolize it more quickly).

Although caffeine is normally associated with coffee, it is found in medicines and many other foods and drinks, namely:

• tea

• chocolate, cocoa and all other chocolate-flavoured products

• over-the-counter stimulants (e.g. Pro-plus)

• painkillers (e.g. Anadin)

• herbal preparations (e.g. Guarin)

• some cola drinks

• Lucozade

• ‘energy’ drinks (e.g. Red Bull)

To find out how much caffeine you are really consuming, see the main caffeine offenders, opposite.