Caffeine

Lu Yu

Caffeinated drink

Caffeine is a naturally occurring chemical found in various seeds, leaves, nuts, and berries. It serves a dual function in plants: as a toxin against unwanted pests, and as an enticement to pollinators, who are stimulated by it. Common sources of caffeine include coffee seeds (beans), tea leaves, kola nuts, yerba mate leaves, and guarana berries. It is extracted from the plant by steeping in water, a process called infusion. Chemically caffeine is an alkaloid, a non-acidic, nitrogen containing compound. A number of alkaloids are produced by flowering plants (e.g. cocaine from coca, nicotine from tobacco, morphine from poppies) to reduce or avoid being eaten by herbivores.

Specifically, caffeine is a xanthine alkaloid, an organic (carbon-based) compound from which many stimulants are derived. It is the world’s most widely consumed psychoactive drug, but unlike many other psychoactive substances, it is legal and unregulated in nearly all parts of the world. Part of the reason caffeine is classified by the FDA as ‘generally recognized as safe’ is that toxic doses, over 10 grams per day for an adult, are much higher than the typically used doses of under 500 milligrams.

There are several known mechanisms of action to explain the effects of caffeine in humans. One is its ability to block adenosine, a neuromodulator, believed to play a role in promoting sleep and suppressing arousal (it helps to induce torpor in animals that seasonally hibernate). In the absence of caffeine, and when a person is awake and alert, little adenosine is present in central nervous system (CNS) neurons. With a continued wakeful state, over time it accumulates and binds with adenosine receptors, gradually increasing drowsiness and ultimately sleep, a state necessary for metabolic removal of many substances toxic to neurons. When caffeine is consumed it binds with adenosine receptors without turning them on, and thus blocks (antagonizes) the interaction of adenosine with its receptor, temporarily preventing or relieving drowsiness and thus maintaining or restoring alertness. Other effects of caffeine are that it increases epinephrine (adrenaline), and it acts as a phosphodiesterase inhibitor and acetylcholinesterase inhibitor (in both cases it is slowing chemical messengers, functionally delaying the CNS response to metabolic needs). In addition, some of its metabolites (byproducts) have effects as well, such as theobromine, which is a vasoconstrictor (narrows blood vessels) and diuretic (promotes urination).

Caffeine can have both positive and negative health effects. There may be a modest preventative effect against some diseases, including Parkinson’s, heart disease, and certain types of cancer. Some people experience insomnia or sleep disruption if they consume caffeine, especially during the evening hours, but others show little disturbance and the effect of caffeine on sleep is highly variable. Evidence of a risk during pregnancy is equivocal, with some authorities concluding that it is wise for pregnant women to limit consumption to the equivalent of two cups of coffee per day or less. Drug dependence, an adaptive state associated with a withdrawal syndrome upon cessation of repeated intake, can occur with chronic caffeine use, and tolerance to increased blood pressure, heart rate and urine production develops.

Caffeine can also stimulate faster and clearer flow of thought, increased focus, and better general body coordination. The amount of caffeine needed to produce effects varies from person to person, depending on body size and degree of tolerance. Effects begin less than an hour after consumption, and a moderate dose usually wears off in about five hours. In shift workers it leads to fewer mistakes caused by tiredness. There is evidence that caffeine can have an added benefit at high altitude. In athletics, moderate doses can improve sprint, endurance, and team sports performance, but the improvements are usually not very large. Caffeine increases intraocular pressure in those with glaucoma but does not appear to affect normal individuals. It may protect people from liver cirrhosis. There is no evidence that coffee stunts a child’s growth. Caffeine may increase the effectiveness of some medications including ones used to treat headaches. Intravenous caffeine is often used in hospitals to provide temporary pain relief for headaches caused by low cerebrospinal fluid pressure.

When doses of caffeine equivalent to 2–3 cups of coffee are administered to people who have not consumed caffeine during prior days, they produce a mild increase in urinary output. Because of this diuretic effect, some authorities have recommended that athletes or airline passengers avoid caffeine to reduce the risk of dehydration. Most people who consume caffeine, however, ingest it daily. Regular users of caffeine have been shown to develop a strong tolerance to the diuretic effect, and studies have generally failed to support the notion that ordinary consumption of caffeinated beverages contributes significantly to dehydration, even in athletes.

Caffeine can have negative effects on anxiety disorders. A number of clinical studies have shown a positive association between caffeine and anxiogenic effects and/or panic disorder. At high doses, typically greater than 300 mg, caffeine can both cause and worsen anxiety or, rarely, trigger mania or psychosis. In moderate doses, caffeine may reduce symptoms of depression and lower suicide risk. In moderate doses, caffeine typically does not affect learning or memory, and can improve cognitive functions, especially in people who are fatigued, possibly due to its effect on alertness. For some people, anxiety can be very much reduced by discontinuing caffeine use. Withdrawal symptoms – including headaches, irritability, inability to concentrate, drowsiness, insomnia, and pain in the stomach, upper body, and joints – may appear within 12 to 24 hours after discontinuation of caffeine intake, peak at roughly 48 hours, and usually last from 2 to 9 days. In prolonged caffeine users, symptoms such as increased depression and anxiety, nausea, vomiting, physical pains and intense desire for caffeine are also reported.

Common sources of caffeine are coffee, tea, soft drinks and energy drinks, caffeine supplements, and (to a lesser extent) chocolate derived from cocoa beans. Less commonly used sources of caffeine include the yerba mate, guarana, and ilex guayusa plants, 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. The disparity in experience and effects between the various natural caffeine sources could be because 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 that can form insoluble complexes with caffeine. In addition to beverages, caffeine is found in a number of other products including pills, transdermal patches, soaps, lip balms, and chewing gums.

One of the world’s primary sources of caffeine is the coffee ‘bean,’ from which coffee is brewed. Caffeine content in coffee varies widely depending on the type of coffee bean and the method of preparation used; even beans within a given bush can show variations in concentration. In general, one serving of coffee ranges from 80 to 100 milligrams, for a single shot (30 milliliters) of arabica-variety espresso, to approximately 100–125 milligrams for a cup (120 milliliters) of drip coffee. Arabica coffee typically contains half the caffeine of the robusta variety. In general, dark-roast coffee has very slightly less caffeine than lighter roasts because the roasting process reduces a small amount of the bean’s caffeine content. Tea contains more caffeine than coffee by dry weight. A typical serving, however, contains much less, since tea is normally brewed much weaker. Also contributing to caffeine content are growing conditions, processing techniques, and other variables. Thus, 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. 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. Chocolate derived from cocoa beans 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. A typical 28-gram serving of a milk chocolate bar has about as much caffeine as a cup of decaffeinated coffee, although dark chocolate has about the same caffeine as coffee by weight. Some dark chocolate currently in production contains as much as 160 mg per 100 g – which is double the caffeine content of the highest caffeinated drip coffee by weight.

The history of tea dates back to ancient China: according to legend, the emperor Shennong, reputed to have reigned in about 3000 BCE, accidentally discovered the beverage when he noted that when certain leaves fell into boiling water, a fragrant and restorative drink resulted. Shennong is also mentioned in Lu Yu’s ‘Cha Jing,’ a famous early work on the subject of tea. The earliest credible evidence of either coffee drinking or knowledge of the coffee tree appears in the middle of the fifteenth century, in the Sufi monasteries of southern Arabia. From Mocha in Yemen, coffee spread to Egypt and North Africa, and by the 16th century, it had reached the rest of the Middle East, Persia, and Turkey. From the Middle East, coffee drinking spread to Italy, then to the rest of Europe, and coffee plants were transported by the Dutch to the East Indies and to the Americas. Kola nut use 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. The earliest evidence of cocoa bean use comes from residue found in an ancient Mayan pot dated to 600 BCE. Also, chocolate was consumed in a bitter and spicy drink called xocolatl, often seasoned with vanilla, chile pepper, and achiote. Xocolatl was believed to fight fatigue, a belief 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. Xocolatl was introduced to Europe by the Spaniards, and became a popular beverage by 1700. The Spaniards 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 an emetic (vomit-causing) tea called ‘asi’ or the ‘black drink.’ Archaeologists have found evidence of this use far into antiquity, possibly dating to Late Archaic times (2500 BCE).

In 1819, German chemist Friedlieb Ferdinand Runge isolated relatively pure caffeine for the first time; he called it ‘Kaffebase’ (i.e. a base that exists in coffee). According to Runge, he did this at the behest of German statesman Johann Wolfgang von Goethe. In 1821, caffeine was isolated both by the French chemist Pierre Jean Robiquet and by another pair of French chemists, Pierre-Joseph Pelletier and Joseph Bienaimé Caventou, according to Swedish chemist Jöns Jacob Berzelius in his yearly journal. Furthermore, Berzelius stated that the French chemists had made their discoveries independently of any knowledge of Runge’s or each other’s work. However, Berzelius later acknowledged Runge’s priority in the extraction of caffeine, stating: ‘However, at this point, it should not remain unmentioned that Runge (in his ‘Phytochemical Discoveries,’ 1820, pages 146–147) specified the same method and described caffeine under the name ‘Caffeebase’ a year earlier than Robiquet, to whom the discovery of this substance is usually attributed, having made the first oral announcement about it at a meeting of the Pharmacy Society in Paris.’ Pelletier’s article on caffeine was the first to use the term in print (in the French form ‘Caféine’ from the French word for coffee: ‘café’). It corroborates Berzelius’s account: ‘Caffeine, noun (feminine). Crystallizable substance discovered in coffee in 1821 by Mr. Robiquet. During the same period – while they were searching for quinine in coffee because coffee is considered by several doctors to be a medicine that reduces fevers and because coffee belongs to the same family as the cinchona [quinine] tree – on their part, Messrs. Pelletier and Caventou obtained caffeine; but because their research had a different goal and because their research had not been finished, they left priority on this subject to Mr. Robiquet. We do not know why Mr. Robiquet has not published the analysis of coffee which he read to the Pharmacy Society. Its publication would have allowed us to make caffeine better known and give us accurate ideas of coffee’s composition …’ Robiquet was one of the first to isolate and describe the properties of pure caffeine, whereas Pelletier was the first to perform an elemental analysis. In 1827, M. Oudry isolated ‘théine’ from tea, but it was later proved that theine was actually caffeine.

Because it was recognized that coffee contained some compound that acted as a stimulant, first coffee and later also caffeine has sometimes been subject to regulation. For example, in the 16th century Islamists in Mecca and in the Ottoman Empire made coffee illegal for some classes. Charles II of England tried to ban it in 1676, Frederick II of Prussia banned it in 1777, and coffee was banned in Sweden at various times between 1756 and 1823. 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 the caffeine in its drink was ‘injurious to health.’ Although the judge ruled in favor of Coca-Cola, two bills were introduced to the 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. Currently the FDA limits beverages to 0.02% caffeine by volume, but caffeine powder, which is sold as a dietary supplement, is unregulated.

Some Seventh-day Adventists, Church of God (Restoration) adherents, and Christian Scientists do not consume caffeine. Some from these religions believe that one is not supposed to consume a non-medical, psychoactive substance, or believe that one is not supposed to consume a substance that is addictive. The Church of Jesus Christ of Latter-day Saints (Mormonism) has said: ‘With reference to cola drinks, the Church has never officially taken a position on this matter, but the leaders of the Church have advised, and we do now specifically advise, against the use of any drink containing harmful habit-forming drugs under circumstances that would result in acquiring the habit. Any beverage that contains ingredients harmful to the body should be avoided.’ Gaudiya Vaishnavas (Hare Krishnas) generally also abstain from caffeine, because they believe it clouds the mind and over-stimulates the senses. To be initiated under a guru, one must have had no caffeine, alcohol, nicotine or other drugs, for at least a year. Though caffeinated beverages are widely consumed by Muslims today, in the 16th century, some Muslim authorities made unsuccessful attempts to ban them as forbidden ‘intoxicating beverages’ under Islamic dietary laws (hallal).

Caffeine has a significant effect on spiders, causing erratic construction of their webs. It is toxic to birds, dogs, and certain other animals. This is at least partly due to a poorer ability to metabolize the compound. Caffeine also has a pronounced effect on mollusks. Some bacteria can live on pure caffeine, and can cleave caffeine into carbon dioxide and ammonia.

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