Caffeine is the world's most popular drug. The white, bitter-tasting, crystalline substance was first isolated from coffee in 1820. Both words, caffeine and coffee, are derived from the Arabic word qahweh (pronounced 'kahveh' in Turkish). The origins of the words reflect the spread of the beverage into Europe via Arabia and Turkey from north-east Africa, where coffee trees were cultivated in the 6th century. Coffee began to be popular in Europe in the 17th century. By the 18th century plantations had been established in Indonesia and the West Indies.
The caffeine content of coffee beans varies according to the species of the coffee plant. Beans from Coffea arabica, grown mostly in Central and South America, contain about 1.1% caffeine. Beans from Coffea robusta, grown mostly in Indonesia and Africa, contain about 2.2% caffeine. Caffeine also occurs in cacao pods and hence in cocoa and chocolate products; in kola nuts, used in the preparation of cola drinks; and in the ilex plant, from whose leaves the popular South American beverage yerba mate is prepared.
Caffeine is also found in tea. It was first isolated from tea leaves in 1827 and named 'theine' because it was believed to be a distinctly different compound from the caffeine in coffee. Tea leaves contain about 3.5% caffeine, but a cup of tea usually contains less caffeine than a cup of coffee because much less tea than coffee is used during preparation.
In North America, the caffeine content of a cup of coffee averages about 75 mg, but varies widely according to cup size, the method of preparation, and the amount of coffee used. Generally, cups prepared from instant coffee contain less caffeine (average 65 mg) and cups prepared by drip methods contain more caffeine (average 110 mg). Cups of tea average about 30 mg, but the range is also largetfrom 10 to 90 mg.
Cola drinks contain about 35 mg caffeine per standard 280 mL serving, with some 5% of the caffeine being a component of kola nuts and most of the remainder being added in the form of a by-product of the decaffeination of coffee and tea. Caffeine- containing soft drinks account for more than 65% of soft drink consumption. A cup of hot chocolate contains about 4 mg caffeine, and a 50-gram chocolate bar between 5 and 60 mg, increasing with the quality of the chocolate. Caffeine is an ingredient of certain headache pills (30-65 mg). It is the main ingredient of non-prescription 'stay-awake' pills (100-200 mg).
Caffeine taken in beverage form begins to reach all tissues of the body within five minutes. Peak blood levels are reached in about 30 minutes. Half of a given dose of caffeine is metabolized in about four hours t more rapidly in smokers and less rapidly in newborn infants, in women in late pregnancy, and in sufferers from liver disease. Normally, almost all ingested caffeine is metabolized. Less than 3% appears unchanged in urine, and there is no day-to-day accumulation of the drug in the body.
Short-term effects of a drug are those that appear soon after a single dose and disappear within hours. Ingestion of the amount of caffeine in one or two cups of coffee (75-150 mg) causes many mild physiological effects. General metabolism increases - expressed as an increase in activity or raised temperature, or both. The rate of breathing increases, as does urination and the levels of fatty acids in the blood and of gastric acid in the stomach. (However, at least one other component of coffee also increases gastric acid secretion. Therefore ulcer sufferers may not achieve relief by switching to decaffeinated coffee.)
Caffeine use may increase blood pressure.
Caffeine stimulates the brain and behavior. Use of 75-150 mg of caffeine elevates neural activity in many parts of the brain, postpones fatigue, and enhances performance at simple intellectual tasks and at physical work that involves endurance but not fine motor coordination. (Caffeine-caused tremor can reduce hand steadiness.)
Caffeine's effects on complex intellectual tasks and on mood do not lend themselves to a simple summary. The effects depend on the personality of the user, on the immediate environment, on the user's knowing whether caffeine has been taken, and even on the time of day.
The effects of caffeine on sleep are clear-cut: taken before bedtime, it usually delays sleep onset, shortens overall sleep time, and reduces the 'depth' of sleep. After using caffeine, sleepers are more easily aroused, move more during sleep, and report a reduction in the quality of sleep. The effects of caffeine on dreaming are less clear.
Larger doses of caffeine, especially when given to non-users, can produce headache, jitteriness, abnormally rapid heartbeat (tachycardia), convulsions, and even delirium. Near-fatal doses cause a crisis resembling the state of a diabetic without insulin, including high levels of blood sugar and the appearance of acetone-like substances in urine. The lowest known dose fatal to an adult has been 3,200 mg - administered intravenously by accident. The fatal oral dose is in excess of 5,000 mg - the equivalent of 40 strong cups of coffee taken in a very short space of time.
Tolerance refers to the body's 'getting used' to a drug with its repeated taking. It is difficult to study the tolerance of human subjects to the various effects of caffeine because nearly everyone in our society uses caffeine regularly in one form or another. Careful research has suggested that tolerance develops to most of caffeine's effects - meaning that, with experience of the drug, the same dose produces a reduced effect, or a larger dose is required to produce the same level of effect.
Regular use of upwards of 350 mg of caffeine a day causes physical dependence on the drug. This means that interruption of the regular use produces a characteristic withdrawal syndrome, the most conspicuous feature of which is an often severe headache that can be relieved by taking caffeine. Absence of caffeine also makes regular users feel irritable and tired. Relief from these withdrawal effects is often given as a reason for using caffeine.
Long-term effects of a toxic nature do not appear evident when regular caffeine use is below about 650 mg a day - equivalent to about eight or nine average cups of coffee. Above this level, users may suffer from chronic insomnia, persistent anxiety and depression, and stomach ulcers. Caffeine use appears to be associated with irregular heartbeat and may raise cholesterol levels, but there is no firm evidence that caffeine causes heart disease.
The evidence is also unclear concerning caffeine and cancer. Caffeine and some of its metabolites can cause changes in the cells of the body and in the way in which they reproduce themselves, and caffeine certainly enhances this kind of action by some known carcinogens. However, although caffeine is suspected as a cause of cancer, the evidence is contradictory and does not allow a clear conclusion. Some animal studies suggest that caffeine can have anti-cancer properties. For example, in rats it prevents breast cancer caused by diethylstilbestrol (the 'morning after' pill).
Caffeine certainly has the ability to cause a variety of reproductive effects in animals, including congenital abnormalities and reproductive failures, reduced fertility, prematurity, and low birth weight. What is unknown is whether these findings are relevant to the use of ordinary amounts of caffeine-containing beverages by pregnant women. Pregnant women have been advised to restrict caffeine intake by both Canadian and United States governments. Pregnant smokers should be especially wary.
The most common medicinal use of caffeine is as a part of headache preparations and other pain relievers. Caffeine is added both for its specific ability to relieve headache, including that caused by caffeine withdrawal, and for its ability to help analgesics do their work better.
The ability of caffeine to stimulate breathing is used in the treatment of apnea (cessation of breathing) in newborn babies, and as an antidote against the depression of breathing by overdoses of heroin and other opiate drugs.
More controversial therapeutic uses of caffeine are these: to kill skin funguses; to improve sperm mobility; to enhance the toxic effects of chemicals used in cancer therapy; and to facilitate the production of seizures during electroconvulsive therapy.
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