Caffeine: Chemical | Organic composition
Last modified: Thursday, 25. December 2008 - 8:50 am
Caffeine, the active substance responsible for the stimulant effect of the coffee plant’s berry, is a methylxanthine, one of the family of stimulants present in more than 60 species of plants. The pure chemical forms white, bitter-tasting crystals, which were first isolated from coffee in 1820. Other family members are theo-phylline, found in tea leaves, and theobromine, found in the cacao pods that are ground to make chocolate. The most potent component in the coffee family by unit weight is theophylline, while theobromine, the weakest component by unit weight, stays in the body longer than does caffeine.
Caffeine is also a trimethylxanthine, which is made up of three methyl groups. Efforts by the liver to deactivate caffeine at first appear counterproductive. Liver enzymes usually detoxify potentially harmful chemicals obtained through food, or those naturally present in the body. But what is left after the liver initially removes a methyl from caffeine are theophylline and paraxanthine, both of which are still active. Only when the final methyl is stripped away is the chemical inert. This production of active metabolites is why the stimulant lasts a relatively long time. It is also why people with liver disease, or those who consume other drugs that engage the liver enzymes, cannot efficiently clear caffeine from their body. Impaired caffeine metabolism is also evident in women taking estrogen for birth control or who are at the high estrogen phase of their monthly cycle. Newborn babies whose livers are not yet fully developed also break down caffeine more slowly until the enzymes are fully activated.
The methylxanthine molecule is built on a foundation common to many biologic compounds, the xanthine double ring of carbons. The three methylxanthines, caffeine, theophylline, and theobromine, all block the action of the body’s adenosine molecule, sending a signal that helps slow the chemical buildup inside cells. Because the methylxanthines closely resemble adenosine at the molecular level, they can occupy the molecular sites on cells that normally recognize, and react to, adenosine. Caffeine prevents the normal slowing action of adenosine at the cellular level, in both nerves and muscle.
Scientists working with cell and tissue preparations recognized that caffeine and the other methylxanthines can block an enzyme called phosphodiesterase. It seems now, however, that this action is carried out at caffeine doses that are much higher than what people normally consume. A similar caveat goes for the supposed action of caffeine on calcium stores in muscle. It is an effect only evident at high doses.
Caffeine is present in coffee, tea, and chocolate. These plant-derived beverages and foods also contain the other methylxanthines, which some scientists say serve as defense chemicals for leaves and berries produced in climates where there is no winter to kill off chewing bugs. Tea contains mostly caffeine, with small amounts of theophylline and theobromine, but tea is a weaker plant extract than the stronger brew, coffee. Theobromine is the primary methylxanthine found in cocoa, which also contains a small amount of caffeine per cup. Caffeine content ranges from as little as 5 mg in a cup of hot cocoa to 300 mg in 6 oz (177 ml) of espresso. Colas have about 50 mg per 12 fl oz (355 ml).
The robusta strain of coffee plant cultivated in Indonesia and Africa contains about 2.2% caffeine, while the arabica variety, grown in Central and South America, contains half that concentration. The caffeine in tea was purified in 1827, and was initially given its own name of “theine,” as chemists of the day thought it different from the caffeine in coffee.
The kola nut, source of some of the flavoring of cola drinks, also has a bit of caffeine. About 5% of the 35 mg in a standard 9.5 oz (280 ml) serving of cola is naturally present from the kola nuts. The caffeine in sodas is added by the manufacturer.
Caffeine is available by prescription as a solution of caffeine citrate. Caffeine is also an active ingredient in many headache medicines, both by prescription and sold over the counter, as well as in nonprescription aids and herbal preparations for alertness and dieting. Body builders may readily buy and use a “stack,” a pill comprising of ephedra, caffeine, and aspirin. Often caffeine is added intentionally to the mixes in today’s energy drinks. Many abused illegal drugs, as well as some drugs sold legally, contain caffeine, either for added effect, or as a “filler,” used in powder form to cut the potency of street drugs.