Caffeine - 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

TABLE 9.3
Caffeine interactions with other substances SOURCE: Prepared by Information Plus from various data sources.

Substance	Interaction
Alcohol	Slows down the metabolism of caffeine
Tobacco	Speeds up the metabolism of caffeine
Birth control pills	Slow down the metabolism of caffeine
Monoamine oxidase (MAO) inhibitors (used to treat depression) and some tranquilizers	May have reduced effectiveness due to caffeine's stimulating effects
Decongestants	Have effects similar to caffeine, so jitteriness, insomnia, or irritability may be made worse

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.