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Caffeine is a chemical compound found naturally in such foods as coffee beans, tea, cacao beans (chocolate, but in much smaller amounts), kola nuts, maté, and guarana. It is well known for its characteristic, intensely bitter taste, and as a stimulant of the central nervous system, heart, and respiration. It is also a diuretic. It is added to some soft drinks such as colas and Mountain Dew.
Caffeine is an alkaloid of the methylxanthine family, which also includes the similar compounds theophylline and theobromine. In its pure state it is an intensely bitter white powder. Its chemical formula is C8H10N4O2, its systematic name is 1,3,7-trimethylxanthine or 3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione, and its structure is shown above.
Pure caffeine occurs as odorless, white, fleecy masses, glistening needles or powder.
The main source of caffeine in food industry are the coffee beans. The caffeine content can vary significantly. In 2004 some trees were found in Ethiopia that contain 15 times less caffeine than average. Beans from such trees may be used in the future to produce better quality decaffeinated coffee.
One dose of caffeine is generally considered to be 100 mg, delivered by one 5 fl oz / 1.5 dl cup of drip coffee or one (or one-half) caffeine tablet. Real-world coffee varies considerably in caffeine content per cup, from about 75 to 250 mg. Tea and cola contain somewhat less caffeine per serving than coffee, while yerba mate contains significantly more.
The amount of caffeine in some common consumables is approximately as follows:
Caffeine is sometimes called theine when it is found in tea, as the caffeine in tea was once thought to be different than the caffeine found in coffee.
In the European Union, a warning must be placed on packaging if the caffeine content of any beverage exceeds 150 mg per litre. This includes caffeine from any source (including guarana, which is often found in energy drinks). In many countries, caffeine is classified as a flavouring.
Caffeine is thought to act on the brain by blocking adenosine receptors. Adenosine, when bound to receptors of nerve cells, slows down nerve cell activity; this happens, among other times, during sleep. The caffeine molecule, being similar to adenosine, binds to the same receptors but doesn't cause the cells to slow down; instead, the caffeine blocks the receptors and thereby the adenosine action. The resulting increased nerve activity causes the release of the hormone epinephrine, which in turn leads to several effects such as higher heart rate, increased blood pressure, increased blood flow to muscles, decreased blood flow to the skin and inner organs, and release of glucose by the liver. In addition, caffeine, similar to amphetamines, increases the levels of the neurotransmitter dopamine in the brain.
Caffeine is quickly and completely removed from the brain and, unlike other CNS stimulants or alcohol, its effects are short lived. In many people, caffeine does not negatively affect concentration or higher mental functions, and hence caffeinated drinks are often consumed in the course of work.
Continued consumption of caffeine can lead to tolerance. Upon withdrawal, the body becomes oversensitive to adenosine, causing the blood pressure to drop dramatically, leading to headache and other symptoms. Recent studies suggest that caffeine intake (in coffee) may decrease the risk of developing Parkinson's disease, but additional study is needed.
Too much caffeine can lead to caffeine intoxication. The symptoms of this disorder are restlessness, nervousness, excitement, insomnia, flushed face, diuresis, and gastrointestial complaints. They can occur in some people after as little as 250 mg per day. More than 1 g per day may result in muscle twitching, rambling flow of thought and speech, cardiac arrhythmia or tachycardia, and psychomotor agitation. Caffeine intoxication can lead to symptoms similar to panic disorder and generalized anxiety disorder. The LD50 is estimated to be about 192 mg/kg of body mass, or about 72 cups of coffee for an average adult.
While safe for humans, caffeine and its related compounds theobromine and theophylline are considerably more toxic to some other animals such as dogs and horses, due to differences in liver metabolism.
A fascinating recent finding is that intake of caffeine can up to halve a patient's risk of diabetes mellitus type 2. While this was originally noticed in patients who consumed high amounts (7 cups a day), the relationship has now been shown to be linear (Salazar-Martinez 2004).
Caffeine, in its many forms, has been used for its stimulating effects. In modern times, though, the substance can be produced in much higher quantities, and has found its way into many products. Purer forms, such as those in caffeine pills, are available easily. These pills are often used by college students and graveyard shift workers to last an entire night with no sleep.
Caffeine pills have been under media fire for recent and past deaths of students, usually take on the form of a caffeine overdose. Once such example of this was the death North Carolina student, Jason Allen. He swallowed a total of 90 such pills, which is the equivalent of 250 cups of coffee.
Caffeine was isolated by the German chemist Friedrich Ferdinand Runge in 1819. According to the legend, he did this at the instigation of Johann Wolfgang von Goethe (Weinberg & Bealer 2001).
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