CHAPTER 9
CAFFEINE

As Americans sit down to their morning cups of coffee or tea or drink a cola, few think about the fact that they are taking a drug. A drug is any substance that affects the mood or the state and function of the body. According to this definition, the caffeine in many of our favorite beverages is a drug.

SOURCES OF CAFFEINE

Caffeine occurs naturally in the seeds, leaves, or fruits of more than sixty-three plant species throughout the world. The primary sources available in the United States, however, are coffee, tea, cacao (cocoa), and kola (cola) plants. These are grown and produced in tropical locations and shipped all over the world. Two other plants, maté and guarana, are primarily grown and consumed in South America as yerba maté and guarana bars and drinks (soda drinks or brewed hot drinks).

Table 9.1 lists the four major sources of caffeine, the parts of the plants that are consumed, and the locations in which the plants are grown. Of the three species of coffee, coffea arabica L. accounts for about three-quarters of all coffee consumption. Spices and other substances, such as vanilla and chocolate, can be added to make flavored coffees.

The three major tea types (green, oolong, and black) all come from the same species of plant; differences in flavor and color are a result of how the tea leaves are processed. For green tea, the leaves are steamed and dried. For oolong tea, the steamed leaves are partly fermented before they are dried. And for black tea, the steamed leaves are completely fermented before they are dried. As with coffee, spices and other flavorings can also be added to vary the taste of tea.

There are many products on the market today that are called "teas" even though they do not contain tea leaves. Virtually any beverage prepared by steeping substances in hot or boiling water is popularly called a tea. Herbal teas do not contain tea leaves or caffeine.

Varying Amounts of Caffeine

Not all plants contain equal concentrations of caffeine. Different methods of processing and brewing can also affect the amount of caffeine per cup or glass of a beverage. When calculating the amount of caffeine per cup or glass, a person must keep in mind the size of the cup or glass, and whether he or she dilutes coffee or tea with another substance, such as milk.

Of caffeinated drinks, coffee contains the highest concentration of caffeine. (See Table 9.2.) The way it is prepared, however, can change the amount of caffeine it contains. In general, coffee made in a drip-style coffee maker is highest in caffeine content. A six-ounce cup of coffee made by the drip method contains between 110-150 milligrams (mg) of caffeine; percolated coffee contains 64-124 mg of caffeine; and instant coffee contains 40-108 mg. Tea has significantly less caffeine than coffee, but the longer it is allowed to steep, the higher the caffeine concentration. A one-minute brew for a six-ounce cup of tea contains between thirty-five and forty-six mg of caffeine; a three-minute brew contains twenty to forty-six mg of caffeine. A hot cocoa mix typically contains six mg of caffeine. Both cocoa and cola drinks generally have lower levels of caffeine ounce per ounce than tea and coffee. However, cocoa contains large amounts of theobromine, a chemical related to caffeine that has the same stimulating effect.

Consumers should be aware that many popular over-the-counter (OTC, or nonprescription) medications contain caffeine. Caffeine is used in some OTC and prescription pain relievers because some studies have shown that caffeine increases their effectiveness. Caffeine is also a major ingredient in most preparations to help individuals stay awake and in OTC weight-control products.

HOW MUCH CAFFEINE DO WE CONSUME?

Table 3.2 in Chapter 3 shows the per capita consumption of beverages: milk, tea, coffee, bottled water, carbonated soft drinks, fruit juices and fruit drinks, canned iced tea, and vegetable juices. Consumption of carbonated soft drinks generally rose between 1966 and the early 1990s and then leveled off somewhat. Most carbonated soft drinks contain caffeine. Coffee consumption was relatively stable from 1966 through 1976, dropped sharply in 1977, and has stayed somewhat consistent since then with the lowest level of consumption in the mid-1990s. In 2003 coffee consumption was 24.3 gallons per person.

Tea consumption rose somewhat steadily from 1966 through the mid-1970s, somewhat stabilized until 1990, and then rose sharply in the early-to-mid-1990s to somewhat stabilize again. In the mid-1990s, when coffee consumption was down somewhat, tea consumption was up somewhat. In 2003 tea consumption was 7.6 gallons per person.

The average daily intake of caffeine among consumers in the United States is about 280 mg, which is equal to about three cups of coffee or about seven twelve-ounce glasses of a cola beverage (L. M. Juliano and R. R. Griffiths, "A Critical Review of Caffeine Withdrawal: Empirical Validation of Symptoms and Signs, Incidence, Severity, and Associated Features," Psychopharmacology, vol. 176, 2004).

Results of a study published in 2001 (Janet Brown et al., "Misclassification of Exposure: Coffee as a Surrogate for Caffeine Intake," American Journal of Epidemiology, no. 153) show that the four main sources of caffeine for people aged thirty to seventy-five living in southern Ontario, Canada, were brewed coffee, instant coffee, regular tea, and cola soft drinks. Brewed coffee was the main source of caffeine, while tea and cola soft drinks ranked second or third, depending on age. Cola drinks ranked second for those aged thirty to forty-four, and tea ranked second for those aged forty-five to seventy-five. Men had a higher caffeine intake than women, and those aged forty-five to fifty-nine had a higher caffeine intake than younger persons.

Results of a study on beverage caffeine intake in U.S. consumers (C. A. Knight et al., Food and Chemical Toxicology, vol. 42, no. 12, December 2004) were some-what consistent with the Ontario study. Research results revealed that children and young adults up to age twenty-four consumed most of their caffeine in carbonated soft drinks. Consumption of coffee generally did not begin until age fifteen, but children as young as one year old consumed tea. People ages twenty-five and older consumed most of their caffeine in coffee, with carbonated soft drinks a second choice, and tea in third place. When people reached fifty years of age or so, tea became their second-largest source of caffeine, with carbonated soft drinks their third. This "switch" between tea and soft drinks remained throughout the rest of their lives.

The Ontario study also showed that caffeine intake is usually underestimated because people often report only their coffee intake and omit caffeine from other sources. The results of this study showed an average intake of caffeine for subgroups of these Ontario residents to range from a low of 288 mg per day for women ages thirty to forty-four to a high of 426 mg per day for men ages forty-five to fifty-nine.

Coffee remains the major source of caffeine for adults. According to the National Coffee Association's 2003 National Coffee Drinking Trends survey, 51% of the adult population drinks coffee everyday, representing 108.3 million coffee drinkers. Another 28% of the population, or 58.3 million adults, drinks coffee occasionally.

Only a small percentage of eighteen-to-twenty-four-year-olds consumed coffee in 2003—just 7% as estimated by the National Coffee Association. High levels of unemployment are correlated with lower levels of coffee drinking; this age group had the highest level of unemployment of all adults in 2003.

PHYSICAL EFFECTS OF CAFFEINE

Caffeine is classified as a stimulant because it increases the activity of the cardiovascular system, digestive system, and sympathetic nervous system (that which generally mobilizes the body for greater activity), and produces a sense of alertness in the brain. It also has a mild diuretic effect, eliminating water from the body by increasing urination. In moderate amounts, it can increase the ability to work longer and concentrate better. Too much caffeine, however, can produce nervousness, anxiety, irritability, and sleeplessness.

Because it gives athletes quicker reaction and longer endurance times, caffeine is a drug for which Olympic competitors are tested. If more than a small to moderate amount of caffeine (the amount in a few cups of coffee) is found in the blood, an athlete can be disqualified from the Olympic Games and other international competitions.

Many caffeine-producing plants also contain related stimulants known as methylxanthines, two of which are theophylline and theobromine. Theophylline is used in prescription drugs to treat chronic lung diseases such as asthma and emphysema. Theobromine is a weaker stimulant than caffeine, but it is more abundant in cocoa beans than is caffeine. Part of the stimulating effect of chocolate and cocoa is probably due to theobromine.

The fact that caffeine increases alertness has led to the myth that a strong cup of coffee will help to sober up someone who is drunk, but caffeine does not counteract the effects of alcohol.

How Caffeine Is Metabolized

In its pure state, caffeine is a bitter white powder that looks something like cornstarch. It is a member of the purine family of compounds. When purines are broken down in the body, they form a chemical called xanthine. The liver converts xanthine to uric acid, a metabolic waste product.

Caffeine dissolves in water, and it is rapidly and completely absorbed into the blood after ingestion. It takes from four to twelve hours to be eliminated completely from the body. Therefore, drinking coffee, tea, or caffeine-containing soft drinks several times a day can result in a large amount of caffeine in the body.

Two other purines, adenine and guanine, play a major role in human genetics and cell function. One of their by-products, adenosine, participates in the supply of energy to cells and helps regulate body processes such as the transmission of signals by nerves. In addition, adenosine can

• Promote sleepiness.
• Dilate blood vessels.
• Reduce the contractions of the stomach and intestines.
• Prevent seizures.
• Slow the reaction to stress.
• Lower the heart rate, blood pressure, and body temperature.

To perform these functions, adenosine inhibits the release of neurotransmitters (chemicals that carry messages from one nerve cell to another) by binding to specific receptors on a cell's surface. The structure of caffeine and its by-products is chemically similar to that of adenosine, which allows caffeine to bind to the same receptor sites, blocking adenosine and preventing it from taking effect. The effects of caffeine are the result of this blocking of the "slowing" effects of adenosine and explain why ingesting large amounts of caffeine may result in the "caffeine jitters."

IS CAFFEINE ADDICTIVE?

The question of whether caffeine is addictive has been debated for decades. Some medical experts believe it is mildly addictive because it fits the criteria for addiction: dependence and tolerance. In "Clinical Pharmacology of Caffeine" (Annual Review of Medicine, 1990), Neal L. Benowitz observed, "Minor criteria for addiction liability include the development of tolerance, physical dependence, and recurrent intense desire for the drug, all of which are characteristic of regular caffeine consumers. Thus, there is a group of coffee drinkers who appear to be addicted to caffeine, although the extent of caffeine addiction in the population is unknown."

While caffeine is both psychoactive (mood altering) and addictive, it is not intoxicating. No one gets drunk or "high" on caffeine, although it can produce anxiety and sleeplessness.

However, results of a 1999 study, "Are We Dependent upon Coffee and Caffeine? A Review on Human and Animal Data" (Neuroscience and Biobehavioral Reviews), show that complete tolerance to many of the effects of caffeine on the central nervous system does not occur. Additionally, average daily doses of caffeine do not act on brain structures related to reward, motivation, and addiction as do "hard" drugs such as cocaine and amphetamines.

HEALTH EFFECTS

One major side effect of consuming large quantities of coffee, tea, soft drinks, and chocolate is a nervous feeling or jitters. In general, the more caffeine that is consumed, the more likely the person is to suffer these side effects. For some people, however, even a minor amount of caffeine can disrupt their sleeping patterns, cause their hands to shake, or create anxiety.

The physical effects of caffeine in the body are fairly well understood, but studies attempting to link caffeine to different diseases have been inconclusive. For example, scientists know that caffeine stimulates the central nervous system, resulting in increased alertness and mood elevation. However, for persons in good general health, studies have not shown any link between drinking coffee or tea and suffering from a nervous disorder, other than the temporary side effects discussed above.

Caffeine does raise blood pressure. Some people develop a tolerance to this effect, and the blood pressure soon returns to its normal level. However, some do not develop this tolerance. Caffeine causes a persistent rise in blood pressure among some regular consumers, even when their daily intake is moderate (W. R. Lovall et al., "Blood Pressure Response to Caffeine Shows Incomplete Tolerance after Short-Term Regular Consumption," Hypertension, vol. 43, no. 4, April 2004). In "Critical Review of Dietary Caffeine and Blood Pressure: A Relationship That Should Be Taken More Seriously," J. E. James contends that caffeine use could account for 14% of coronary heart disease deaths and 20% of stroke deaths (Psychosomatic Medicine, vol. 66, no. 1, January-February 2004).

Coffee has also been suspected of increasing cholesterol levels in the blood, but research data are some-what contradictory. Results from a Norwegian study found that drinking filtered coffee was not associated with high cholesterol levels, but that consumption of boiled coffee promoted increased plasma concentration of cholesterol and was thus associated with an elevated risk for cardiovascular disease (T. Ranheim and B. Halvorsen, "Coffee Consumption and Human Health—Beneficial or Detrimental?" Molecular Nutrition and Food Research, vol. 49, no. 3, March 2005). In contrast, P. Happonen et al. determined that brewing method does not make a difference, and concluded from their data that heavy coffee consumption increases the short-term risk of heart attack and death ("Coffee Drinking Is Dose-Dependently Related to the Risk of Acute Coronary Events in Middle-Aged Men," Journal of Nutrition, vol. 134, no. 9, September 2004). Moreover, results of a Nigerian study conducted by A. J. Onuegbu and E. O. Agbedana suggest that shortterm consumption of coffee may increase the total serum cholesterol and LDL (bad) cholesterol levels ("The Effects of Coffee Consumption on Serum Lipids and Lipoprotein in Healthy Individuals," African Journal of Medicine and Medical Sciences, vol. 30, no. 1-2, March–June 2001).

Caffeine Overdose

It is possible to overdose on caffeine. Symptoms of an overdose include hyperventilation (rapid, deep breathing), rapid heartbeat, atrial heart fibrillation (twitching; beating unevenly), convulsions, and imbalances in the body's levels of potassium, sugar, and other blood chemicals. The overdose amount differs from person to person and depends on body weight, metabolic rate, and usual intake of caffeine (tolerance).

Fatal caffeine overdoses are very rare, but they can occur. Most are either suicide attempts or accidental overuse of caffeine tablets. An average-sized adult would have to consume about 5,000 milligrams (five grams) of caffeine—about fifty cups of normal-strength coffee—to get a fatal dose, and the cups would have to be drunk in rapid succession. In children, because of their smaller body mass and differences in metabolizing caffeine, a much smaller dose could be lethal.

Is There a Link to Cancer?

Results of studies to determine the links (if any) between caffeine and various types of cancer have been contradictory. For every study that gives evidence of a possible link, another study finds no evidence of a link. Results of laboratory studies have shown that caffeine can change the cells of bacteria, plants, insects, and humans in the laboratory, but results of epidemiological studies have not shown that caffeine causes cancerous cell development in generally healthy people. In a 1997 report (Nutrition and the Prevention of Cancer: A Global Perspective), the American Institute of Cancer Research in Washington, D.C., and the World Cancer Fund in London stated that "most evidence suggests that regular consumption of coffee and/or tea has no significant relationship with the risk of cancer of any site."

Results of a 2005 Harvard study, which used large data sets from the Nurses' Health Study (women) and the Health Professionals' Follow-up Study (men), support the findings reported in the previous paragraph, in that consumption of caffeinated coffee or tea, or caffeine from other sources, was not associated with the incidence of colon or rectal cancer. Conversely, regular consumption of decaffeinated coffee was associated with a reduced incidence of rectal cancer (K. B. Michels et al., "Coffee, Tea, and Caffeine Consumption and Incidence of Colon and Rectal Cancer," Journal of the National Cancer Institute, vol. 97, no. 4, February 2005).

Caffeine and Pregnancy

While heavy caffeine use has been suspected of contributing to miscarriages, some studies have given conflicting results and failed to establish a definite link (L. B. Signorello and J. K. McLaughlin, "Maternal Caffeine Consumption and Spontaneous Abortion: A Review of

the Epidemiologic Evidence," Epidemiology, vol. 15, no. 2, March 2004).

The U.S. Food and Drug Administration (FDA) advises pregnant women to limit or eliminate their intake of caffeine. The substances that an expectant mother eats or drinks can be passed through the bloodstream to her unborn baby, and a mother who drinks large amounts of caffeine may produce a baby who shows signs of caffeine jitters. Nursing mothers can also pass caffeine to their babies through breast milk, leading to sleep disruptions and irritability.

Interactions with Other Drugs

Caffeine may also interact with prescription and OTC drugs. In some cases, a drug may have side effects similar to those of caffeine, so even a small amount of coffee, tea, or cola may cause jitteriness or disturb sleep. In other cases, caffeine may reduce or heighten the effectiveness of medications. In addition, alcohol and tobacco affect the metabolism of caffeine in the body, causing it either to leave the body more rapidly or to remain in the bloodstream for a longer time. (See Table 9.3.) People who drink a lot of caffeinated beverages should discuss with their doctors the effects caffeine might have on any medications they are taking.

Possible Health Benefits

Caffeine's bronchodilator effect of opening the air-ways can be beneficial to people suffering from acute bronchial asthma. Caffeine acts as an analgesic (pain killer) and, when combined with ibuprofen, can bring faster and longer lasting relief from tension headaches. It is often prescribed for migraine headaches. Drinking two cups of coffee before breakfast has helped individuals suffering from dizziness and other effects caused by abnormally low blood pressure.

DECAFFEINATION

People who are sensitive to caffeine or those who want to moderate their caffeine intake can still enjoy their favorite beverages in decaffeinated forms. Decaffeination removes almost all the caffeine (about 97%) from coffee or tea. There are three common methods of decaffeination.

• The direct method uses methylene chloride, which dissolves caffeine, to remove caffeine from green coffee beans and moist tea leaves. Then a further process removes the methylene chloride from the product.
• The water method uses water to dissolve the caffeine from steamed coffee beans or tea leaves. Then the caffeine is removed from the water by using methylene chloride, and the decaffeinated water is added back to the coffee or tea to enhance flavor. The beans or leaves are steamed again to remove any methylene chloride remaining.
• The carbon dioxide method, which is the newest, uses carbon dioxide to remove caffeine. This process leaves in more flavor than the other two methods.

Methylene chloride, in its inhaled form, is known to cause cancer in laboratory animals. When methylene chloride is diluted in their drinking water, however, the laboratory animals do not develop cancer. The FDA has analyzed decaffeinated coffee made through the direct method and found that so little methylene chloride is left in the final product that any risk of it causing cancer is remote. The amount of methylene chloride in the finished product is less than that found in the air on a smoggy day.

Some people find that decaffeinated coffee lacks some of the flavor of regular coffee. Using fresh-ground or flavored decaffeinated coffee beans may help brew a better-tasting pot of coffee. Using half regular coffee and half decaffeinated coffee can also help cut down caffeine intake, as can simply drinking fewer caffeineladen drinks per day. Hot chocolate, hot apple cider, and herbal teas make good low-caffeine or caffeine-free substitutes for those wanting to limit their caffeine intake.

What Do They Do with the Caffeine They Take Out?

The caffeine removed from coffee and tea is a useful by-product. It can be used in medications or added to soft drinks to increase their caffeine content. Some is processed into theophylline, which is used in medications for asthma and emphysema.