Caffeine is a central nervous system (CNS) stimulant, having the effect of temporarily warding off drowsiness and restoring alertness. When caffeine is added to foods and beverages in the United States, it must appear in the list of ingredients on the label. But manufacturers aren't required to list the amount of caffeine. This is true in many other countries as well.Beverages containing caffeine, such as coffee, tea, soft drinks and energy drinks enjoy great popularity; caffeine is the world's most widely consumed psychoactive substance, but unlike most other psychoactive substances, it is legal and unregulated in nearly all jurisdictions. In North America, 90% of adults consume caffeine daily.The U.S. Food and Drug Administration lists caffeine as a "Multiple Purpose GRAS (Generally Recognized As Safe) Food Substance".
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 contain as much as 80 milligrams of caffeine per serving, but others, such as the Wired X294 contains 294 milligrams of caffeine. 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.
When humans drink or eat caffeine, it acts as a stimulant (say: stim-yuh-lunt). Stimulants may make us feel more awake and alert. Many people drink liquids with caffeine because they think it helps them to wake up and feel sharper.For most people, moderate doses of caffeine — 200 to 300 milligrams (mg) a day — aren't harmful. However, excessive caffeine — more than 500 mg a day — can cause irritability, nervousness, anxiety, insomnia, headaches and diarrhea.
Caffeine can cause your heart to pump faster and your breathing to quicken. Caffeine is also a diuretic (say: dye-yuh-reh-tik). This means that caffeinated drinks or foods cause you to urinate (pee) more often than normal.It may also increase your blood pressure. The amount of caffeine in two to three cups of coffee can raise systolic pressure 3 to 14 millimeters of mercury (mm Hg) and diastolic pressure 4 to 13 mm Hg in people without high blood pressure.Caffeine does not accumulate in the bloodstream nor is it stored in the body. It is excreted in the urine many hours after it has been consumed.
Caffeine will not reduce the effects of alcohol, although many people still believe a cup of coffee will "sober-up" an intoxicated person.Caffeine may be used as a treatment for migraine headaches and in relieving, for a short time, fatigue or drowsiness .
Drinking caffeinated beverages on a regular basis may provide significant protection against death from heart disease in the elderly who have normal levels of blood pressure, according to data from a large U.S. health and nutrition study.
Drinking caffeinated beverages may induce a "healthy" rise in blood pressure that counteracts the drop in blood pressure that occurs after a meal, a phenomenon that becomes more pronounced as people age, researchers note.
Among 6,594 adults participating in the study, 426 died of heart disease during a 9-year period. For subjects 65 years of age or older, the researchers found that greater daily consumption of caffeinated beverages was associated with a lower risk of death from heart disease. This acted in a dose-response fashion - the higher the caffeine level, the lower the risk, and visa versa.
People who consumed four or more servings of caffeinated beverages daily had a 53-percent lower risk of death from heart disease compared with those who consumed less than half a serving daily. Subjects who consumed two to four servings per day had a 32-percent lower risk of dying from heart disease.
Caffeinated ground coffee and caffeinated instant coffee, both of which have relatively large amounts of caffeine per serving, were the only specific beverages associated with a statistically significant protective effect, the authors note.
This apparent protective effect of caffeinated coffee consumption was not seen in people with severe high blood pressure or those who were younger than 65 years of age.
Studies on caffeine and heart disease have yielded conflicting results, note principal investigator Dr. James A. Greenberg and colleagues from Brooklyn College of the City University of New York. "It is possible that the conflict is due to differences between nonelderly and elderly persons," they point out, noting that one study found that drinking coffee increased the risk in younger subjects and that the level of risk decreased with increasing age.
Another study by Dr. Sarah A. Rosner, of Harvard School of Public Health, Boston, Massachusetts, and colleagues prospectively examined the effect of coffee consumption on the risk of heart attack in 32,650 Swedish women between 40 and 74 years of age.
The women were participating in a study initiated between 1987 and 1990. During an average follow-up of 5.1 years, a total of 459 heart attacks occurred. Of these, 391 were nonfatal and 68 were fatal.
In analyses adjusting for possible confounding factors, the team found that women who drank 5 or more cups of java per week had a 32 percent reduced relative risk of having a heart attack compared with women who drank 0 to 4 cups per week, although this did not reach statistical significance.
As mentioned, caffeine may protect against heart disease death in the elderly by preventing a decline in blood pressure after meals, a phenomenon that becomes increasing more pronounced with age.
If confirmed, the current findings could have important ramifications, the authors conclude, given that coffee is widely consumed and heart disease is one of the leading causes of death in the elderly.There are "several plausible biologic mechanisms" by which coffee may reduce risk of heart attack, Rosner's team explains. "Coffee contains phenolic compounds, which are known antioxidants and may reduce oxidative stress," they note. Additionally, coffee has been shown to improve the body's use of insulin and may protect against type 2 diabetes.
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