Caffeine beverage consumption is a worldwide habit. Coffee, cola drinks, tea, and mate contain caffeine. It is a naturally occurring substance belonging to the family of xanthine stimulants, and is found in at least 60 different plant species.
Although coffee and tea are the most common sources of caffeine in North America and Europe, residents of other parts of the world use different plants to make stimulating drinks. In South America the native mate plant contains caffeine, and, especially in Argentina, a tea made from it is very popular. Inhabitants of India, tropical Africa, and the West Indies chew kola nuts for their stimulating effect. From there the nuts are exported around the world for the manufacture of cola drinks.
Recent studies in Canada and Australia show that only a small portion of the population in those countries do not consume coffee or tea. In Canada 7.6 percent of the population do not drink these beverages on a daily basis, while in Australia the figure is only 3 percent.
In the United States, average caffeine consumption is estimated to be 200 milligrams per day. This is roughly equivalent to two cups of coffee per person, but this estimate includes every man, woman, and child, and is therefore an inaccurate picture of adult consumption. Other studies in the United States, Australia, and Canada found that 30 percent of the respondents were consuming 500 to 600 milligrams of caffeine a day. In Sweden a 17-year study showed that only 3 percent of men over 50 abstained from drinking coffee, and that the consumption per person for those aged 57 in 1980 averaged 4-2 cups per day. 1 Researchers have found similar consumption levels in middle-aged men and women in the United States recently. In addition, they found the amount of caffeine intake from all sources to be approximately 25 percent higher than that calculated from drinking coffee and tea, and only 3 percent of the study group had no caffeine intake from any source. 2
Caffeine probably ranks as the most frequently used drug in the world. Even taking into consideration the use of tobacco, alcohol, and marijuana, it may still rank as the most abused drug. And tea and coffee are not the only sources of caffeine. Various drugs, prescription and nonprescription painkillers, and cold medications also contain it. One common but little recognized source of caffeine, both in developed and developing countries, is the apparently innocent soft drink so frequently consumed by children and youth. Table 1 lists the caffeine content of a number of soft drinks.
Risks from caffeine
In recent years worldwide concern has been expressed about the dangers of high caffeine consumption. The concern is related to many areas of disease. The health risks include heart attack, psychological disorders, and cancer of various organs including the bladder, pancreas, ovary, and breast. A possible link to birth defects prompted the U.S. Food and Drug Administration (PDA) to issue a strong warning against consumption of caffeine by pregnant women.
The FDA initiated a large-scale animal study in which researchers fed rats varying levels of caffeine equivalent to 12 to 24 cups of strong coffee per day. At these high levels rats gave birth to babies with toes or parts of toes missing. 3 In addition they found that when the mother received caffeine in amounts equivalent to only two cups of coffee per day, the fetuses showed retarded bone growth. 4, 5
Belgian research has uncovered evidence linking coffee to birth defects in humans. 6 The researchers surveyed 202 mothers of infants with birth defects for various environmental and dietary factors. They found a significant relationship between coffee consumption and birth defects.
Finnish researchers have shown that as little as two cups of coffee can decrease placental blood flow by 25 percent. 7 Recent findings relating maternal smoking to a decrease in mental acuity in newborns, possibly caused by low oxygen delivery, may signal trouble for mothers using caffeinated beverages, since lower blood flow may also cause lower oxygen delivery. 8
Experiments investigating the effects of caffeine's interaction with other chemicals have shown that caffeine can cause a wide variety of apparently unrelated compounds to become toxic, producing physical defects in the developing embryo and fetus. 9 Interestingly, high levels of caffeine alone in embryo cell cultures were shown to have little effect. But caffeine combined with a carcinogen resulted in both genetic changes and embryo toxic effects. 10 Genetic effects appear to be intensified in the presence of caffeine because caffeine prevents the repair of DNA in the genes after chemical damage.11
Research has shown that the typical infant born in America has a blood caffeine level equivalent to that produced by drinking one or two cups of coffee. 12 The drug action of the caffeine takes several days to wear off because the infant's liver is unable to metabolize caffeine.
Some researchers are concerned that this may also pose problems to the fetus. During the second and third trimester of pregnancy, from the fourth to the ninth month, caffeine remains in the system two or three times longer than normal. This is thought to be caused by changing hormonal levels in the mother. Similar findings have been observed in women taking oral contraceptives. Table 2 shows how age and contraceptive use change the time needed for elimination of caffeine from the blood.
It takes five to six hours for an average adult to eliminate half a dose of caffeine. During the next five to six hours, half the remaining caffeine (or 25 percent of the original dose) is removed. And during the third six-hour period half of the remaining 25 percent (or 12.5 percent) is removed. Notice that during the first trimester clearance is only slightly increased, to a full six hours, but in the second and third trimesters, the time required for half elimination of caffeine doubles or triples.
Caffeine and calcium
Yet another effect of caffeine on the human system has to do with the body's ability to maintain its supply of calcium. 13 This important mineral helps in the formation of bones. Calcium excretion in the urine increases proportionally with the amount of caffeine a person consumes. In addition, excretion of magnesium and sodium also increases.
Unlike some experiments in which large amounts of caffeine were involved, the above findings came from experiments performed among healthy college girls, using amounts of caffeine similar to those commonly consumed by regular coffee drinkers. 14
Figure 1 compares the total calcium loss when no caffeine is ingested with the losses resulting from ingestion of an amount equal to that of from one and one-half cups of coffee to the equivalent of two to three cups.
Furthermore, when a person regularly consumes coffee, tea, or any of the cola drinks over a number of years, there is reason for concern about gradual thinning of the bones. This thinning is so gradual as to go almost undetected, but it nevertheless takes place continuously. Recent FDA research has shown that in mice, as little as the equivalent of about three cups of coffee per day was sufficient to cause bone deficiencies when the dose was ingested all at once. 15
Another problem compounds the calcium situation still further, especially for women in the United States. The U.S. Department of Agriculture findings show that the diet of the average young woman does not contain sufficient calcium and magnesium to meet the recommended daily allowance. As the consumption of caffeine-containing beverages increases, the intake of dairy products, which are high in calcium and magnesium, typically decreases. This decreased intake, along with increased excretion because of caffeine consumption, poses the potential for serious deficiencies.
Caffeine and the mind
Caffeine also appears to have a greater effect upon the mental processes than once thought. The American Psychiatric Association now recognizes caffeinism as a disorder affecting as many as one in ten people whose consumption of caffeine is more than 500 milligrams per day. This condition can be brought about by as few as four cups of coffee per day (depending on the type of coffee consumed), seven to nine cups of tea per day, or nine colas per day.
Caffeinism is indistinguishable from anxiety neurosis, and until recently was not recognized as being in any way different. It has been observed that psychiatric patients consuming large amounts of caffeine show more acute symptoms, have generally poorer health, and resort more frequently to behaviormodifying drugs. 16 Similar findings appear to be true for hospital patients generally. 17 Initially caffeine causes a low-level stress response, excites the nervous system, and increases gastricacid secretion and heart rate and rhythm. Furthermore, it constricts blood vessels, thereby increasing blood pressure, and causes the bronchial muscles to relax, thus opening the way for greater air intake.
Caffeine consumption by children has recently been shown to have the same effect as upon adults, although the description of the symptoms is different. In adults high caffeine consumption appears to cause nervousness, irritability, anxiety, restlessness, agitation, muscle tremors, sleeplessness, and headaches. When children exhibit these symptoms, they are said to be nervous and jittery, easily frustrated, easily upset, and impatient when their demands are not met immediately. These symptoms have been strongly linked to hyperactive behavior in children, and one study showed that one third of the children with high levels of caffeine consumption could be diagnosed as hyperactive. 18 In addition, chronic or regular consumption of caffeine appears to cause a drop in classroom participation, although this particular result needs further study.
In a recent review of the relationship between caffeine use and cancer of the bladder, one researcher concluded that coffee is at least a weak bladder carcinogen, and that if further evidence was needed to clear up that question, then researchers would need to study for a decade a population of more than 10,000 people with low coffee intake, such as Mormons or Seventh-day Adventists. 19 Within two months a study of 24,000 Seventh-day Adventists was published. Investigators studying the Seventh-day Adventists were able to show that those individuals consuming two or more cups of coffee per day had double the risk of developing fatal bladder cancer. The study also showed an increase in fatal colon cancer with the same levels of consumption. 20
Inhibition of iron absorption is another health risk lying in wait for the tea and coffee drinker. Coffee can cause a 40 percent decrease in iron absorption. Tea can cause absorption to decrease by two thirds. 21
Although tea and coffee have not been conclusively linked with increased death rates, one must keep in mind that as long as any product such as caffeine, coffee, or tea has any commercial interest involved, there will be a controversy over whether to support health or profits. The problem arises when those supporting profit present themselves as health supporters looking for honest answers.
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