Coffee ingestion on average is about a third of that of tap water in North America and Europe.[1] Worldwide, 6.7 million metric tons of coffee were produced annually in 1998–2000, and the forecast is a rise to 7 million metric tons annually by 2010.[69]
Scientific studies have examined the relationship between coffee consumption and an array of medical conditions. Findings are contradictory as to whether coffee has any specific health benefits, and results are similarly conflicting regarding the negative effects of coffee consumption.[8]
Coffee consumption has been shown to have minimal or no impact, positive or negative, on cancer development;[71] however, researchers involved in an ongoing 22-year study by the Harvard School of Public Health state that "the overall balance of risks and benefits [of coffee consumption] are on the side of benefits."[71] Various other studies have shown apparent reductions in the risks of Alzheimer's disease, Parkinson's disease, heart disease, diabetes mellitus type 2, cirrhosis of the liver,[72] and gout. A longitudinal study in 2009 showed that moderate drinkers of coffee (3-5 cups per day) had lower chances of developing dementia, in addition to Alzheimer's disease [73]. It increases the risk of acid reflux and associated diseases.[74] Some health effects of coffee are due to its caffeine content, as the benefits are only observed in those who drink caffeinated coffee while others appear to be due to other components.[75] For example, the antioxidants in coffee prevent free radicals from causing cell damage.[76]
Caffeine is the major coffee constituent which the coffee tolerance or intolerance depends on. In a healthy liver, the majority of caffeine is degraded by the hepatic microsomal enzymatic system. Caffeine is mostly degraded to paraxanthine substances, partially to theobromine and theophylline, and a small amount of unchanged caffeine is excreted by urine. Therefore, the metabolism of caffeine depends on the state of this enzymatic system of the liver. Elderly individuals with a depleted enzymatic system do not tolerate coffee with caffeine. They are recommended to take decaffeinated coffee, and this only if their stomach is healthy, because both decaffeinated coffee and coffee with caffeine cause heartburn. Moderate amounts of coffee (50-100 mg of caffeine or 5-10 g of coffee powder a day) are well tolerated by a majority of elderly people, who enjoy to meet and chat over a cup of coffee. Excessive amounts of coffee, however, can in many individuals cause very unpleasant, exceptionally even life-threatening side effects.[77]
Coffee consumption can lead to iron deficiency anemia in mothers and infants.[78] Coffee also interferes with the absorption of supplemental iron.[79]
American scientist Yaser Dorri has suggested that the smell of coffee can restore appetite and refresh olfactory receptors. He suggests that people can regain their appetite after cooking by smelling coffee beans, and that this method can also be used for research animals.[80] Many high end perfume shops now offer coffee beans to refresh the receptors between perfume tests.
Over 1,000 chemicals have been reported in roasted coffee; more than half of those tested (19/28) are rodent carcinogens.[81] Coffee's negative health effects are often blamed on its caffeine content. Research suggests that drinking caffeinated coffee can cause a temporary increase in the stiffening of arterial walls.[82] Coffee is no longer thought to be a risk factor for coronary heart disease.[83] Some studies suggest that it may have a mixed effect on short-term memory, by improving it when the information to be recalled is related to the current train of thought but making it more difficult to recall unrelated information.[84] About 10% of people with a moderate daily intake (235 mg per day) reported increased depression and anxiety when caffeine was withdrawn,[85] and about 15% of the general population report having stopped caffeine use completely, citing concern about health and unpleasant side effects.[86]
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