Caffeine is a chemical found in some foods and beverages that stimulates the nervous system and increases alertness and energy. Though caffeine is a drug, a moderate amount -- two to four cups of coffee per day -- is generally not harmful. An excess of caffeine may be linked to heart disease and/or bone loss, but studies are inconclusive. Caffeine is addictive, and those coming off the drug experience withdrawal symptoms.
Filter coffee provides the most amount of caffeine of any food or beverage. A 225 g (8 oz) cup contains around 175 mg of caffeine. A double shot of espresso contains about 100 mg of caffeine.
A 225 g (8 oz) cup of black tea contains between 40 to 60 mg of caffeine. Oolong is the next-most caffeinated tea, with 12 to 55 mg. Green tea contains a lesser amount of caffeine, around 15 mg. White tea contains only about 6 to 25 mg. Herbal tea contains no caffeine.
Energy drinks like Red Bull contain quite a lot of caffeine, about 80 mg per 225 g (8 oz) serving. They usually also contain taurine, a detoxifier that helps maintain the body's energy levels during while exercise.
Most soft drinks contain caffeine. The major brands and flavours contain a standard amount of between 40 to 60 mg per 225 g (8 oz). Some fizzy energy drinks contain more caffeine.
Chocolate is one of the few foods that contain caffeine, though it is an extremely small amount. The caffeine level in chocolate is similar to that of decaf coffee, about 5 mg per 225 g (8 oz) portion.