Caffeine is a naturally occurring plant alkaloid, found in the leaves, seeds or fruits of more than 60 plants, where it acts as a natural pesticide that paralyses and kills insects feeding upon them. The main requirement for the majority of caffeine-containing plants is to have ample sunshine and rain, and therefore they grow best in tropical or sub-tropical regions. The biggest producer of coffee today is Brazil, responsible for around 28% of the total global production of coffee plants. Colombia and then Indonesia follow. Total global production comes from over 70 different nations.
The most commonly used plants containing caffeine are coffee, tea and cocoa. Other less commonly used sources include the plants yerba mate and guarana, which are sometimes used in the preparation of teas and, more recently, energy drinks. Two of caffeine's alternative names, mateine and guaranine, are derived from the names of these plants.
Caffeine is also a common ingredient of soft drinks such as cola, originally produced from kola nuts, and is used as a flavour in many other beverages.
The amount of caffeine in food products varies depending on the serving size, the type of product, and preparation method. With teas and coffees, the plant variety also affects caffeine content.
Caffeine’s production comes in several different forms. The oldest form of use comes from its homeland in Ethiopia where coffee beans were dried and crushed as a food source. During its spread into the Islamic sector, caffeine was usually used as a beverage made from infusing ground roasted beans. This was the same method and production that was later used in Europe.
Caffeine is a central nervous system and metabolic stimulant, and is used both recreationally and medically to reduce physical fatigue and help restore mental alertness. Caffeine stimulates the central nervous system resulting in increased alertness and wakefulness, faster and clearer flow of thought, increased focus, and better general body coordination. The precise amount of caffeine necessary to produce effects varies depending on body size and degree of tolerance to caffeine.
Caffeine is sometimes administered in combination with medicines to increase their effectiveness, such as for the treatment of migraine or with certain pain relievers such as aspirin. Caffeine may also be used to overcome the drowsiness caused by antihistamines.
Caffeine is metabolized in the liver by the cytochrome P450 oxidase enzyme system (specifically, the 1A2 isozyme) into three metabolic dimethylxanthines, which each have their own effects on the body:
Paraxanthine increases lipolysis, leading to elevated glycerol and free fatty acid levels in the blood plasma.
Theobromine (the principal alkaloid in cocoa) dilates the blood vessels and increases urine volume.
Theophylline relaxes the bronchi, and is used to treat asthma.
Each of these metabolites is further metabolised and then excreted in the urine.