The caffeine in coffee, tea, cocoa, chocolate and cola drinks acts as a stimulant, but depending on the strength, there may be more in tea than in coffee.
The following gives a comparison of the caffeine content of different foodstuffs:-
- 100 mL. of brewed coffee contains 60 to 130 mg.
- 100 mL. of instant coffee contains 40 to 100 mg.
- 100 mL. of tea contains 40 to 60 mg.
- 100 mL. of cola drink contains 10 mg.
- 100 g. of chocolate contains 20 to 30 mg.
Some medications designed to stimulate, prevent sleep, ease fatigue and prevent motion sickness also contain caffeine.
Caffeine acts on the body to increase alertness, increase the rate at which the body metabolises (burns) food, and increase urine production. In large doses, it may produce headache, irritability, insomnia, psychiatric conditions and stomach upsets, and it can aggravate diabetes, heart disease, depression and anxiety disorders. If taken before going to bed, a short, less restful sleep can be expected. People who have any of the foregoing conditions should limit their caffeine intake.
There are some connections between moderate to large doses of caffeine and problems such as miscarriage, premature birth and stillbirth in pregnancy. Pregnant women should therefore limit themselves to two to four cups of tea, coffee or cola a day.
An overdose of caffeine causes anxiety, restlessness, irritability and sleeplessness. It is possible to develop a mild addiction to caffeine.