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Caffeine

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Caffeine
File:Caffeine.png
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Infobox disclaimer and references


Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a psychoactive stimulant drug. Caffeine was discovered by a German chemist, Friedrich Ferdinand Runge, in 1819. He coined the term "kaffein", a chemical compound in coffee, which in English became caffeine.[1] Caffeine is also part of the chemical mixtures and insoluble complexes guaranine found in guarana, mateine found in mate, and theine found in tea; all of which contain additional alkaloids such as the cardiac stimulants theophylline and theobromine, and often other chemicals such as polyphenols which can form insoluble complexes with caffeine.[2]

Caffeine is found in varying quantities in the beans, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants. It is most commonly consumed by humans in infusions extracted from the cherries of the coffee plant and the leaves of the tea bush, as well as from various foods and drinks containing products derived from the kola nut. Other sources include yerba mate, guarana berries, and the Yaupon Holly.

In humans, caffeine is a central nervous system (CNS) stimulant, having the effect of temporarily warding off drowsiness and restoring alertness. Beverages containing caffeine, such as coffee, tea, soft drinks and energy drinks enjoy great popularity. Caffeine is the world's most widely consumed psychoactive substance, but unlike many other psychoactive substances it is legal and unregulated in nearly all jurisdictions. In North America, 90% of adults consume caffeine daily.[3] The U.S. Food and Drug Administration lists caffeine as a "Multiple Purpose Generally Recognized as Safe Food Substance".[4]

Caffeine has diuretic properties, at least when administered in sufficient doses to subjects who do not have a tolerance for it.[5] Regular users, however, develop a strong tolerance to this effect,[5] and studies have generally failed to support the common notion that ordinary consumption of caffeinated beverages contributes significantly to dehydration.[6][7][8]

Contents

[edit] Occurrence

File:Roasted coffee beans.jpg
Roasted coffee beans, the world's primary source of caffeine

Caffeine is found in many plant species, where it acts as a natural pesticide, with high caffeine levels being reported in seedlings that are still developing foliages, but are lacking mechanical protection;[9] caffeine paralyzes and kills certain insects feeding upon the plant.[10] High caffeine levels have also been found in the surrounding soil of coffee bean seedlings. It is therefore understood that caffeine has a natural function as both a natural pesticide and as an inhibitor of seed germination of other nearby coffee seedlings thus giving it a better chance of survival.[11]

The most commonly used caffeine-containing plants are coffee, tea, and to a lesser extent cocoa.[12] Less commonly used sources of caffeine include the yerba maté and guarana plants,[13] which are sometimes used in the preparation of teas and energy drinks. Two of caffeine's alternative names, mateine and guaranine, are derived from the names of these plants.[14][15] Some yerba mate enthusiasts assert that mateine is a stereoisomer of caffeine, which would make it a different substance altogether.[13] This is not true because caffeine is an achiral molecule, and therefore has no enantiomers; nor does it have other stereoisomers. The disparity in experience and effects between the various natural caffeine sources could be due to the fact that plant sources of caffeine also contain widely varying mixtures of other xanthine alkaloids, including the cardiac stimulants theophylline and theobromine and other substances such as polyphenols which can form insoluble complexes with caffeine.[16]

The world's primary source of caffeine is the coffee "bean" (which is actually the seed of the coffee plant), from which coffee is brewed. Caffeine content in coffee varies widely depending on the type of coffee bean and the method of preparation used;[17] even beans within a given bush can show variations in concentration. In general, one serving of coffee ranges from 40 milligrams, for a single shot (30 milliliters) of arabica-variety espresso, to about 100 milligrams for a cup (120 milliliters) of drip coffee. Generally, dark-roast coffee has less caffeine than lighter roasts because the roasting process reduces the bean's caffeine content.[18][19] Arabica coffee normally contains less caffeine than the robusta variety.[17] Coffee also contains trace amounts of theophylline, but no theobromine.

Tea is another common source of caffeine. Although tea contains more caffeine than coffee, a typical serving contains much less, as tea is normally brewed much weaker. Besides strength of the brew, growing conditions, processing techniques and other variables also affect caffeine content. Certain types of tea may contain somewhat more caffeine than other teas. Tea contains small amounts of theobromine and slightly higher levels of theophylline than coffee. Preparation and many other factors have a significant impact on tea, and color is a very poor indicator of caffeine content.[20] Teas like the pale Japanese green tea gyokuro, for example, contain far more caffeine than much darker teas like lapsang souchong, which has very little.

Caffeine is also a common ingredient of soft drinks such as cola, originally prepared from kola nuts. Soft drinks typically contain about 10 to 50 milligrams of caffeine per serving. By contrast, energy drinks such as Red Bull can start at 80 milligrams of caffeine per serving. The caffeine in these drinks either originates from the ingredients used or is an additive derived from the product of decaffeination or from chemical synthesis. Guarana, a prime ingredient of energy drinks, contains large amounts of caffeine with small amounts of theobromine and theophylline in a naturally occurring slow-release excipient.[21]

Chocolate derived from cocoa contains a small amount of caffeine. The weak stimulant effect of chocolate may be due to a combination of theobromine and theophylline as well as caffeine.[22] Chocolate contains too little of these compounds for a reasonable serving to create effects in humans that are on par with coffee. A typical 28-gram serving of a milk chocolate bar has about as much caffeine as a cup of decaffeinated coffee.

In recent years various manufacturers have begun putting caffeine into shower products such as shampoo and soap, claiming that caffeine can be absorbed through the skin.[23] However, the effectiveness of such products has not been proven, and they are likely to have little stimulatory effect on the central nervous system because caffeine is not readily absorbed through the skin.[24]

Various manufacturers market caffeine tablets, claiming that using caffeine of pharmaceutical quality improves mental alertness. These effects have been borne out by research that shows that caffeine use (whether in tablet form or not) results in decreased fatigue and increased attentiveness.[25] These tablets are commonly used by students studying for their exams and by people who work or drive for long hours.[26]

[edit] History

File:CoffeePalestineStereo.jpg
A coffeehouse in Palestine, circa 1900
Main articles: History of cocoa, History of coffee, Origin and history of tea

Humans have consumed caffeine since the Stone Age.[27] Early peoples found that chewing the seeds, bark, or leaves of certain plants had the effects of easing fatigue, stimulating awareness, and elevating one's mood. Only much later was it found that the effect of caffeine was increased by steeping such plants in hot water. Many cultures have legends that attribute the discovery of such plants to people living many thousands of years ago.

According to one popular Chinese legend, the Emperor of China Shennong, reputed to have reigned in about 3000 BC, accidentally discovered that when some leaves fell into boiling water, a fragrant and restorative drink resulted.[28] Shennong is also mentioned in Lu Yu's Cha Jing, a famous early work on the subject of tea.[29] The history of coffee has been recorded as far back as the ninth century. During that time, coffee beans were available only in their native habitat, Ethiopia. A popular legend traces its discovery to a goatherder named Kaldi, who apparently observed goats that became elated and sleepless at night after browsing on coffee shrubs and, upon trying the berries that the goats had been eating, experienced the same vitality. The earliest literary mention of coffee may be a reference to Bunchum in the works of the 9th century Persian physician al-Razi. In 1587, Malaye Jaziri compiled a work tracing the history and legal controversies of coffee, entitled "Undat al safwa fi hill al-qahwa". In this work, Jaziri recorded that one Sheikh, Jamal-al-Din al-Dhabhani, mufti of Aden, was the first to adopt the use of coffee in 1454, and that in the 15th century the Sufis of Yemen routinely used coffee to stay awake during prayers.

Towards the close of the 16th century, the use of coffee was recorded by a European resident in Egypt, and about this time it came into general use in the Near East. The appreciation of coffee as a beverage in Europe, where it was first known as "Arabian wine," dates from the 17th century. During this time "coffee houses" were established, the first being opened in Constantinople and Venice. In Britain, the first coffee houses were opened in London in 1652, at St Michael's Alley, Cornhill. They soon became popular throughout Western Europe, and played a significant role in social relations in the 17th and 18th centuries.[30]

The kola nut, like the coffee berry and tea leaf, appears to have ancient origins. It is chewed in many West African cultures, individually or in a social setting, to restore vitality and ease hunger pangs. In 1911, kola became the focus of one of the earliest documented health scares when the US government seized 40 barrels and 20 kegs of Coca-Cola syrup in Chattanooga, Tennessee, alleging that the caffeine in its drink was "injurious to health".[31] On March 13, 1911, the government initiated The United States v. Forty Barrels and Twenty Kegs of Coca-Cola, hoping to force Coca-Cola to remove caffeine from its formula by making claims, such as that the excessive use of Coca-Cola at one girls' school led to "wild nocturnal freaks, violations of college rules and female proprieties, and even immoralities." Although the judge ruled in favor of Coca-Cola, two bills were introduced to the U.S. House of Representatives in 1912 to amend the Pure Food and Drug Act, adding caffeine to the list of "habit-forming" and "deleterious" substances which must be listed on a product's label.

The earliest evidence of cocoa use comes from residue found in an ancient Mayan pot dated to 600 BC. In the New World, chocolate was consumed in a bitter and spicy drink called xocoatl, often seasoned with vanilla, chile pepper, and achiote. Xocoatl was believed to fight fatigue, a belief that is probably attributable to the theobromine and caffeine content. Chocolate was an important luxury good throughout pre-Columbian Mesoamerica, and cocoa beans were often used as currency.

Xocoatl was introduced to Europe by the Spaniards and became a popular beverage by 1700. They also introduced the cacao tree into the West Indies and the Philippines. It was used in alchemical processes, where it was known as Black Bean.

The leaves and stems of the Yaupon Holly (Ilex vomitoria) were used by Native Americans to brew a tea called Asi or the Black Drink the use of which among Native American groups archaeologists have demonstrated to stretch back far into antiquity, possibly dating to Late Archaic times.

[edit] Synthesis and properties

Anhydrous (dry) USP-grade caffeine

In 1819, the German chemist Friedrich Ferdinand Runge isolated relatively pure caffeine for the first time. According to Runge, he did this at the behest of Johann Wolfgang von Goethe.[32] In 1827, Oudry isolated "theine" from tea, but it was later proved by Mulder and Jobat that theine was the same as caffeine.[32] The structure of caffeine was elucidated near the end of the 19th century by Hermann Emil Fischer, who was also the first to achieve its total synthesis.[33] This was part of the work for which Fischer was awarded the Nobel Prize in 1902. The nitrogen atoms are all essentially planar (in sp2 orbital hybridisation), resulting in the caffeine molecule having aromatic character. Being readily available as a byproduct of decaffeination, caffeine is not usually synthesized.[34] If desired, it may be synthesized from dimethylurea and malonic acid.[35]

[edit] Physical and psychological effects of caffeine

Caffeine has widespread physical and physiological effects these are covered in a seperate article. See Physical and psychological effects of caffeine


[edit] See also


[edit] References

  • Weinberg BA, Bealer BK. The world of caffeine. New York & London: Routledge, 2001. ISBN 0-415-92722-6.
  • Note (1): Noever, R., J. Cronise, and R. A. Relwani. 1995. Using spider-web patterns to determine toxicity. NASA Tech Briefs 19(4):82. Published in New Scientist magazine, 27 April 1995.
  • JE James and KP Stirling, "Caffeine: A Summary of Some of the Known and Suspected Deleterious Habits of Habitual Use," British Journal of Addiction, 1983;78:251-58.
  • Hughes JR, McHugh P, Holtzman S. "Caffeine and schizophrenia." Psychiatr Serv 1998;49:1415-7. Fulltext. PMID 9826240.
  • Shannon MW, Haddad LM, Winchester JF. Clinical Management of Poisoning and Drug Overdose, 3rd ed.. 1998. ISBN 0721664091.
  • Diagnostic and Statistical Manual of Mental Disorders ISBN 0890420610
  • Trice, I., and Haymes, E. (1995). "Effects of caffeine ingestion on exercise-induced changes during high intensity, intermittent exercise". International Journal of Sports Nutrition. 37-44.
  • Tarnopolsky, M. A. (1994). "Caffeine and endurance performances". Sports Medicine (Vol. 18 Ed. 2): 109 – 125.
  • Ivy, J., Costill, D., Fink, W. et al. (1979). "Influence of caffeine and carbohydrate feedings on endurance performance". Medical Science Sports Journal (Vol. 11). 6-11.
  • Dews, P.B. (1984). "Caffeine: Perspectives from Recent Research". Berlin: Springer-Valerag.
  • Cornelis MC, El-Sohemy A, Kabagambe EK, Campos H. Coffee, CYP1A2 genotype, and risk of myocardial infarction JAMA. 2006 Mar 8;295(10):1135-41 PMID 16522833

[edit] External links

Look up this page on
Wiktionary: Caffeine

[edit] Caffeine toxicity


Stimulants edit

Caffeine Nicotine Modafinil Adrafinil Armodafinil

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