Caffeine

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Caffeine is a chemical found in the beans, seeds, leaves, or bark of many plants. Caffeine is considered a chemical stimulant of the nervous system. A chemical stimulant speeds things up both mentally and physically, increasing alertness, interfering with sleep, and raising heart rate and blood pressure.

Foods and beverages made from caffeine-containing substances are widely available in and accepted by most contemporary societies. In North America, the most common food sources of caffeine include coffee, tea, and chocolate. More than 80 percent of adults in North America consume caffeine regularly. Average per capita (per person) caffeine intake in the United States has been estimated at 211 milligrams per day, in Canada at 238 milligrams, in Sweden at 425 milligrams, and in the United Kingdom at 444 milligrams per day. The world's per capita caffeine consumption is about 70 milligrams per day.

Even though caffeine-containing foods and beverages are perfectly legal and very commonly used, caffeine can affect behavior in ways that are similar to the effects of drugs of abuse. People who regularly use caffeine can experience both physical dependence and tolerance.

Caffeine has known effects on the brain. As little as 32 milligrams of caffeine, less than the amount of caffeine in most 12-ounce cola soft drinks, can improve alertness, performance, and reaction time. Doses as low as 10 milligrams, less than the amount of caffeine in some chocolate bars, can alter mood. Regular use of only 100 milligrams of caffeine per day—in other words, drinking one cup of coffee every day—can cause severe withdrawal symptoms if the daily caffeine is stopped abruptly.

Coffee and tea are the world's primary dietary sources of caffeine. Consumption of tea was first documented in China in 350 C.E., although there is some evidence that the Chinese first consumed tea as early as the third century B.C.E. Coffee cultivation began around 600C.E., probably in what is now Ethiopia. Other commonly used items containing caffeine include soft drinks, cocoa products, and medications.

CAFFEINE CONTENT OF COMMON FOODS AND DRINKS
Source	Standard Value (in milligrams)
Coffee (6 oz./180 ml)
ground roasted	102
instant	72
decaffeinated	4
Tea (6 oz./180 ml)
leaf or bag	48
instant	36
Cola Soft Drink
(12 oz./360 ml)	43
Chocolate Milk
(6 oz./180 ml)	4
Chocolate Bar
(1.45–1.75 oz./40–50 g)	7
Milk Chocolate (1.5 oz)	10
Dark Chocolate (1.5 oz)	31
Caffeine-containing over-the-counter medications
analgesics and cold preparations	32
appetite suppressants and stimulants	100

Caffeine is found in more than sixty species of plants. Coffee is derived from the beans (seeds) of several species of Coffea plants, and the leaves of Camellia sinensis plants are used in caffeine-containing teas. Chocolate comes from the seeds or beans of the caffeine-containing cocoa pods of Theobroma cacao trees. In developed countries, soft drinks, particularly colas, provide another common source of dietary caffeine. Only a portion of the caffeine in soft drinks comes from the kola nut (Cola nitida); most of the caffeine is added during manufacturing. Since the 1960s, a marked decrease in coffee consumption in the United States has been accompanied by a substantial increase in the consumption of soft drinks. Matt leaves (Ilex paraguayensis), guarana seeds, and yoco bark are other sources of caffeine for a variety of cultures. The accompanying table shows the amounts of caffeine found in common dietary and medicinal sources. As can be seen in the range of values for each source in this table, the caffeine content can vary widely depending on the method of preparation or commercial brand.

It has long been believed that caffeine stimulates mood and behavior, decreases fatigue, and increases energy, alertness, and activity. Although caffeine's effects in experimental studies have sometimes been subtle (difficult to detect) and variable, dietary doses of caffeine have a variety of effects on mood and performance. Doses below 200 milligrams have been shown to improve vigilance (alert watchfulness) and reaction time and postpone sleep. In addition, the subjects of these studies report increased alertness, energy, motivation to work, desire to talk to people, self-confidence, and well-being. Higher doses can both improve or disrupt performance of complex tasks and can cause nervousness, jitteriness, restlessness, and anxiousness.

Caffeine is an ingredient in a variety of over-the-counter medications such as analgesics or painkillers (particularly to treat headaches), stimulants, and decongestants. It is also used in treatments for menstrual pain and appetite suppressants. Although caffeine is a common ingredient in headache preparations (including some prescription drugs to treat migraine headaches), evidence for caffeine's effectiveness for relieving headaches is limited, as is the evidence for its appetite-suppressant effects. Caffeine has also been used to treat:

• chronic obstructive pulmonary disease
• asthma
• breathing problems in newborns
• overdoses with opioid drugs

Although more research is needed, some researchers are concerned that there may be an association between caffeine intake and such diseases as benign fibrocystic breast disease and cancer of the pancreas, kidney, lower urinary tract, and breast. In a recent survey of physician specialists, more than 65 percent recommended reductions in caffeine in patients with cardiac arrhythmia (irregular heartbeat), palpitations, tachycardia (rapid heartbeat), esophagitis/hiatal hernia, fibrocystic disease, or ulcers, as well as in patients who are pregnant.

Case reports have described individuals who consume large amounts of caffeine—more than one gram (1,000 milligrams) per day. This excessive intake is called caffeinism, and occurs most often in psychiatric patients, drug and alcohol abusers, and anorectic patients. Caffeinism can produce a range of symptoms—muscle twitching, anxiety, restlessness, nervousness, insomnia (inability to fall asleep or stay asleep), rambling speech, tachycardia, cardiac arrhythmia, and sensory disturbances including ringing in the ears and flashes of light. Some research has also linked caffeinism with psychoses and anxiety disorders. Extremely high doses of caffeine—between 5,000 and 10,000 milligrams—can produce convulsions and death and have been shown to produce birth defects in mammals.

The American Psychiatric Association recognizes a condition known as caffeine intoxication, in which high doses of caffeine produce adverse effects. Substantial amounts of caffeine are also used by a small percentage of competitive athletes, who believe that caffeine will enhance their athletic performance, despite rules against such use.

Regular caffeine use can decrease a person's responsiveness to its effects. This result is known as tolerance. At first, daily doses of 250 milligrams of caffeine can cause blood pressure to go up and increase the production of urine and saliva. After several days of caffeine use, however, tolerance develops. With tolerance to caffeine, blood pressure and urine and saliva production return toward normal. Caffeine tolerance has not been well researched, although there is some suggestionthat sleep-disturbing effects and jitteriness noticed when caffeine is first used both lessen after regularly using caffeine.

Uncomfortable symptoms occur when caffeine use is suddenly stopped. Caffeine withdrawal is typically characterized by reports of headache, fatigue, drowsiness, and decreased alertness. Severe withdrawal can interfere with normal functioning and include flu-like symptoms, fatigue, severe headache, nausea, and vomiting. In general, caffeine withdrawal begins twelve to twenty-four hours after stopping caffeine use and lasts from two to seven days. Caffeine withdrawal can occur following termination of caffeine doses as low as 100 milligrams per day, an amount equal to one strong cup of coffee, two strong cups of tea, or three soft drinks. These data indicate that the large majority of the adult population of the United States is at risk for significant disruption of mood and behavior when there are interruptions of daily caffeine consumption.

Addiction: Concepts and Definitions; Chocolate; Coffee; Cola Drinks; Tea.

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