Coffee contains caffeine, which acts as a stimulant. For this reason, it is often consumed in the morning, and during working hours. Students preparing for examinations with late-night "cram sessions" use coffee to maintain their concentration. Office workers take a "coffee break" whenever their energy is diminished.
Recent research has uncovered additional stimulating effects of coffee which are not related to the caffeine. Coffee contains an as yet unknown chemical agent which stimulates the production of cortisone and adrenaline, two stimulating hormones.
For occasions when one wants to enjoy the flavor of coffee with less stimulation, decaffeinated coffee (also called decaf) is available. This is coffee from which most of the caffeine has been removed, by the Swiss water process (which involves the soaking of raw beans to absorb the caffeine) or the use of a chemical solvent such as trichloroethylene ("tri"), or the more popular methylene chloride, in a similar process. Extraction with supercritical carbon dioxide has also been employed.
Decaffeinated coffee usually loses some flavor over normal coffees and tends to be more bitter. There are also tisanes that resemble coffee in taste but contain no caffeine (see below).
Caffeine dependence is widespread and withdrawal symptoms are real. See the caffeine article for more on the pharmacological effects of caffeine.
Coffee increases the effectiveness of pain killersâ€”especially migraine medicationsâ€”and can rid some people of asthma. Some of the beneficial effects may be restricted to one sex, for instance it has been shown to reduce the occurrence of gallstones and gallbladder disease in men. Coffee intake may reduce one's risk of diabetes mellitus type 2 by up to half. While this was originally noticed in patients who consumed high amounts (7 cups a day), the relationship was later shown to be linear (Salazar-Martinez 2004).
Coffee can also reduce the incidence of cirrhosis of the liver and prevent colon and bladder cancers. Coffee can reduce the risk of hepatocellular carcinoma, a variety of liver cancer (Inoue, 2005). Also, coffee reduces the incidence of heart disease, though whether this is simply because it rids the blood of excess fat or because of its stimulant effect is unknown. At the annual meeting of the American Chemical Society in Washington, D.C., on August 28, 2005, chemist Joe Vinson of the University of Scranton presented his analysis showing that for Americans, who as a whole do not consume large quantities of fresh fruits and vegetables, coffee represents by far the largest source of valuable antioxidants in the diet.
Coffee is also a powerful stimulant for peristalsis and is sometimes considered to prevent constipation; it is also a diuretic.
Many people drink coffee for its ability to increase short term recall and increase IQ. It also changes the metabolism of a person so that their body burns a higher proportion of lipids to carbohydrates, which can help athletes avoid muscle fatigue.
Some of these health effects are realized by as little as 4 cups a day (24 U.S. fl oz, 700 mL), but others occur at 5 or more cups a day (32 U.S. fl oz or 0.95 L or more).
Some controversy over these effects exists, since by its nature coffee consumption is associated with other behavioral variables. Therefore it has been variously suggested that the cognitive effects of caffeine are limited to those who have not developed a tolerance, or to those who have developed a tolerance and are caffeine-deprived.
Alternative health practitioners often indulge in coffee enemas for "cleansing of the colon" due to its stimulus of peristalsis, although mainstream medicine has not proved any benefits of the practice.
Caffeinism, a condition which mimics mental illnesses ranging from anxiety and bipolar disorder to schizophrenia and psychosis, is among the more worrisome effects of acute or chronic coffee consumption.
Many coffee drinkers are familiar with "coffee jitters", a nervous condition that occurs when one has had too much caffeine. Coffee can also increase blood pressure among those with high blood pressure, but follow-up studies showed that coffee still decreased the risk of dying from heart disease in the aggregate. Coffee can also cause insomnia in some, while paradoxically it helps a few sleep more soundly. It can also cause anxiety and irritability, in some with excessive coffee consumption, and some as a withdrawal symptom. There are also gender-specific effects, in some PMS sufferers it increases the symptoms, and it can reduce fertility in women, also it may increase the risk of osteoporosis in postmenopausal women, and there may be risks to a fetus if a pregnant woman drinks 8 or more cups a day (48 U.S. fl oz or 1.4 L or more).
A February 2003 Danish study of 18,478 women linked heavy coffee consumption during pregnancy to significantly increased risk of stillbirths (but no significantly increased risk of infant death in the first year). "The results seem to indicate a threshold effect around four to seven cups per day," the study reported. Those who drank eight or more cups a day (48 U.S. fl oz or 1.4 L) were at 220% increased risk compared with nondrinkers. This study has not yet been repeated, but has caused some doctors to caution against excessive coffee consumption during pregnancy.
Decaffeinated coffee is occasionally regarded as a potential health risk to pregnant women, due to the high incidence of chemical solvents used to extract the caffeine. These concerns have almost no basis, however, as the solvents in question evaporate at 80â€“90 Â°C, and coffee beans are decaffeinated before roasting, which occurs at approximately 200 Â°C. As such, these chemicals, namely trichloroethane and methylene chloride, are present in trace amounts at most, and neither pose a significant threat to unborn children. Women still worried about chemical solvents in decaffeinated coffee should opt for beans which use the Swiss water process, where no chemicals other than water are used, although higher amounts of caffeine remain.
The American Journal of Clinical Nutrition published a study in 2004 which tried to discover why the beneficial and detrimental effects of coffee are conflicting. The study concluded that consumption of coffee is associated with significant elevations in biochemical markers of inflammation. This is a detrimental effect of coffee on the cardiovascular system, which may explain why coffee has so far only been shown to help the heart at levels of four cups (20 fl oz or 600 mL) or fewer per day.
Caffeine is toxic in high enough doses. It is impossible though, that a toxic dose will be ingested in the form of common drinks. The LD50 of caffeine is estimated to be 150â€“200 mg per kilogram, equaling roughly 140â€“180 cups of coffee (i.e., 3â€“4 gallons, or 11â€“15 L) for an average adult, and consumed within a very limited timeframe. It has been argued that one would die from the volume of water consumed (due to osmotic imbalances) long before taking the 180th cup. In concentrated forms, such as pills or powders, it can be taken in sufficient quantities to cause vomiting, unconsciousness, and even death. A single box of caffeine pills can be fatal if taken at once.
The health risks of decaffeinated coffee have been studied, with varying results. One variable is the type of decaffeination process used; while some involve the use of organic solvents which may leave residual traces, others rely on steam.
A study has shown that cafestol, a substance which is present in boiled coffee drinks, dramatically increases cholesterol levels, especially in women. Filtered coffee only contains trace amounts of cafestol.