Health effects of coffee
The health effects of coffee have been studied to determine how coffee drinking affects humans. Coffee contains several compounds which are known to affect human body chemistry. The coffee bean itself contains chemicals which are mild psychotropics for humans as a defense mechanism of the Coffee plant. These chemicals are toxic in large doses, or even in their normal amount when consumed by many creatures which may otherwise have threatened the beans in the wild. The primary psychoactive chemical in coffee is caffeine, which acts as a stimulant.
Recent research has uncovered additional stimulating effects of coffee which are not related to its caffeine content. Coffee contains a currently unknown chemical agent which stimulates the production of cortisone and adrenaline, two stimulating hormones.[not in citation given]
A May 2012 study published in the New England Journal of Medicine found that coffee drinkers "who drank at least two or three cups a day were about 10 percent or 15 percent less likely to die for any reason during the 13 years of the study." The researchers who conducted the study said that this does not necessarily provide a cause-and-effect relationship, but will help point other researchers in the right direction.
Decaffeinated coffee (sometimes 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 remove the caffeine) or the use of a chemical solvent such as trichloroethylene ("tri"), or the more popular methylene chloride, in a similar process. Another solvent used is ethyl acetate; the resultant decaffeinated coffee is marketed as "natural decaf" because ethyl acetate is naturally present in fruit. Extraction with supercritical carbon dioxide has also been employed.
Decaffeinated coffee usually loses some flavor compared to normal coffee. There are also coffee alternatives that resemble coffee in taste but contain no caffeine. These are available both in ground form for brewing and in instant form.
All-cause mortality 
In women, coffee consumption significantly decreases all-cause mortality, apparently decreasing somewhat linearly to a relative risk of approximately 0.85 for those drinking 3 cups per day compared to those who consume no coffee, but the relative risk then remains almost the same for up to 6 cups per day, according to a large prospective cohort study in 1993. In men, these beneficial effects were not as great, in fact with an increased risk for those drinking approximately one cup every other day compared to those drinking none, but yet having a significant trend towards less mortality for those who drink more than 2 cups per day compared to those who drink none. Results were similar for decaffeinated coffee. An inverse association between coffee consumption and total and cause-specific mortality was also found in a 2012 analysis of data from the National Institutes of Health–AARP Diet and Health Study.
Reduced risk of Alzheimer's disease and dementia 
Several studies comparing moderate coffee drinkers (defined as 3–5 cups per day) with light coffee drinkers (defined as 0–2 cups per day) found that those who drank more coffee were significantly less likely to develop Alzheimer's disease later in life.  A longitudinal study in 2009 found that moderate coffee drinkers had reduced risk of developing dementia in addition to Alzheimer's disease.
Reduced risk of gallstone disease 
Drinking caffeinated coffee has been correlated with a lower incidence of gallstones and gallbladder disease in both men and women in two studies performed by the Harvard School of Public Health. A lessened risk was not seen in those who drank decaffeinated coffee.
Reduced risk of Parkinson's disease 
A study comparing heavy coffee drinkers (3.5 cups a day) with non-drinkers found that the coffee drinkers were significantly less likely to develop Parkinson's disease later in life. Likewise, a second study found an inverse relationship between the amount of coffee regularly drunk and the likelihood of developing Parkinson's disease.
Cognitive performance 
Likewise, in tests of simple reaction time, choice reaction time, incidental verbal memory, and visuospatial reasoning, participants who regularly drank coffee were found to perform better on all tests, with a positive relationship between test scores and the amount of coffee regularly drunk. Elderly participants were found to have the largest effect associated with regular coffee drinking. Another study found that women over the age of 80 performed significantly better on cognitive tests if they had regularly drunk coffee over their lifetimes. A recent study showed that roast coffee protected primary neuronal cells against hydrogen peroxide-induced cell death.
Caffeine and analgesics 
Coffee contains caffeine, which may increase the effectiveness of gastrointestinal uptake of some pain killers, especially in patients with migraine and headache medications. For this reason, many over-the-counter headache drugs include caffeine in their formula. Caffeine itself does not have analgesic properties. In some patients with migraine, caffeine can alleviate pain by acting on the cerebral blood vessels. A 2012 study suggested caffeinated coffee reduced pain in an office environment.
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. This effect has been attributed to the compounds caffeic acid and chlorogenic acid, which are thought to suppress the formation of human islet amyloid polypeptide (hlAPP).
Liver protection 
Coffee can also reduce the incidence of cirrhosis of the liver and has been linked to a reduced risk of hepatocellular carcinoma, a primary liver cancer that usually arises in patients with preexisting cirrhosis. The exact mechanism and the amount of coffee needed to achieve a beneficial effect have long been unclear. The cytokine transforming growth factor (TGF) beta has long been recognized for promoting fibrosis ability acting through the Smad family of transcription factors. In a report published in the Journal of Hepatology, Gressner and colleagues provide the first mechanistic context for the epidemiological studies on coffee drinkers by showing that caffeine may have potent anti-fibrotic capabilities through its ability to antagonize the Smad pathway.
Coffee consumption is also correlated in Africa to a reduced risk of oral, esophageal, and pharyngeal cancer. In ovarian cancer, no benefit was found. In the Nurses' Health Study and a 2011 Swedish study, a modest reduction in breast cancer was observed in postmenopausal women only, which was not confirmed in decaffeinated coffee, and a reduction in endometrial cancer was observed in people who drank either caffeinated or decaffeinated coffee. The Harvard Medical School reported in 2006 that researchers found that coffee drinkers were 50% less likely to get liver cancer than nondrinkers. Another study found a correlation between coffee consumption (both regular and decaffinated) and a lower risk of aggressive prostate cancer.
Coffee moderately reduces the incidence of dying from cardiovascular disease, according to a large prospective cohort study published in 2008. A 2009 prospective study in Japan following nearly 77,000 individuals aged 40 to 79 found that coffee consumption, along with caffeine intake, was associated with a reduced risk of dying from cardiovascular disease.
A 2012 meta-analysis concluded that people who drank moderate amounts of coffee had a lower rate of heart failure, with the biggest effect found for those who drank more than four cups a day.
Laxative / diuretic 
Coffee is also a powerful stimulant for peristalsis and is sometimes considered to prevent constipation. However, coffee can also cause excessively loose bowel movements. The stimulative effect of coffee consumption on the colon is found in both caffeinated and decaffeinated coffee.
Contrary to popular belief, caffeine does not act as a diuretic when consumed in moderation (less than five cups a day or 500 to 600 milligrams), and does not lead to dehydration or to a water-electrolyte imbalance; current evidence suggests that caffeinated beverages contribute to the body's daily fluid requirements no differently from pure water.
Coffee contains polyphenols such as flavan-3-ols (monomers and procyanidins), hydroxycinnamic acids, flavonols and anthocyanidins. These compounds have antioxidative effect and potentially reduce oxidative cell damage. One particular substance with putative anticarcinogenic effect is methylpyridinium. This compound is not present in significant amounts in other foods. Methylpyridinium is not present in raw coffee beans but is formed during the roasting process from trigonelline, which is common in raw coffee beans. It is present in both caffeinated and decaffeinated coffee, and even in instant coffee. Research funded by Kraft Foods shows that roast coffee contains more lipophilic antioxidants and chlorogenic acid lactones and is more protective against hydrogen peroxide-induced cell death in primary neuronal cells than green coffee. The espresso method of extraction yields higher antioxidant activity than other brewing methods.
Prevention of dental cavities 
The tannins in coffee may reduce the cariogenic potential of foods. In vitro experiments have shown that these polyphenolic compounds may interfere with glucosyltransferase activity of mutans streptococci, which may reduce plaque formation.
Coffee consumption contributes to a decreased risk of gout in men over age 40. In a large study of over 45,000 men over a 12-year period, the risk for developing gout in men over 40 was inversely proportional with the amount of coffee consumed.
Blood pressure 
A 2011 study showed that moderate (≤4 cups per day) coffee consumption was inversely associated with high blood pressure and high triglyceride level in Japanese men. However, the study showed no significant association between coffee consumption and prevalence of metabolic syndrome for Japanese women.
Caffeine dependency 
Over 1,000 chemicals have been reported in roasted coffee, and 19 are known rodent carcinogens; however, most substances cited as rodent carcinogens occur naturally and should not be assumed to be carcinogenic in humans at exposure levels typically experienced in day-to-day life. However, whole coffee extract is suspected to cause cancer of the human pancreas, and there is limited evidence of a weak positive relationship between coffee consumption and bladder cancer in humans. However, more recent follow-up studies to the 1981 study linking coffee consumption to pancreatic cancer have not found any link between coffee consumption and pancreatic cancer. A recent meta-analysis based on 37 case-control and 17 cohort studies (10,594 cases) provided quantitative evidence that coffee consumption was not appreciably related to pancreatic cancer risk, even at high intakes. No significant association between coffee consumption and the risk of gastric and/or pancreatic cancers was found in a more recent prospective study.
Gastrointestinal problems 
Psychological effects and sleep changes 
Many coffee drinkers are familiar with "coffee jitters", a nervous condition that occurs when one has had too much caffeine. It can also cause anxiety and irritability, in some with excessive coffee consumption, and some as a withdrawal symptom. Coffee can also cause insomnia in some. In others it can cause narcolepsy. However an analysis of the Nurses' Health Study concluded depression rates among women decreased with increased consumption of caffeinated coffee.
Caffeine, a major component of coffee, has various psychological effects. A study from Johns Hopkins Medical School suggests that the perceived psychological benefits of caffeine are merely the result of eliminating withdrawal symptoms. The author of Emotional Intelligence 2.0 suggests that chronic caffeine consumption can lead to a decrease in emotional intelligence.
A 2007 study by the Baylor College of Medicine indicates that the diterpenes cafestol and kahweol, found only in coffee beans, may raise levels of low-density lipoprotein or LDL in humans. This increase in LDL levels is an indicator that coffee raises cholesterol. The Baylor study suggests a possible link between cafestol, kahweol and higher levels of cholesterol in the body.
Paper coffee filters have a property that binds to lipid-like compounds which allows the filter to remove most of the cafestol and kahweol found in coffee. Brew methods which do not use a paper filter, such as the use of a press pot, do not remove cafestol and kahweol from the final brewed product.
Blood pressure 
Caffeine has previously been implicated in increasing the risk of high blood pressure; however, recent studies on coffee consumption have not confirmed any association. In a 12-year study of 155,000 female nurses, large amounts of coffee did not induce a "risky rise in blood pressure" . Previous studies had already shown statistically insignificant associations between coffee drinking and clinical hypertension. Effect of coffee on morbidity and mortality due to its effect on blood pressure is too weak, and has not been studied. Other positive and negative effects of coffee on health would be difficult confounding factors.
Effects on pregnancy 
Caffeine molecules are small enough to penetrate the placenta and slip into the baby's blood circulation. Unlike adults, organs and systems in fetuses are not full-fledged, therefore not capable of fully metabolizing caffeine and excreting it. The stimulant tends to linger in the fetus's blood ten times longer than in adults. High levels of caffeine are bound to accumulate in the baby's body with frequent maternal consumption of caffeine. Just like what it does to adults, caffeine could also send the baby's pulse and breathing rate racing and affect its sleep pattern for an extended duration.
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 (64 U.S. fl oz or 1.89 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 also regarded as a potential health risk to pregnant women when chemical solvents are used to extract the caffeine instead of other less invasive processes. The impact of these chemicals is debated, however, as the solvents in question evaporate at 80–90 °C, and coffee beans are decaffeinated before roasting, which occurs at approximately 200 °C. As such, these chemicals, namely trichloroethane and methylene chloride, are present in trace amounts at most, and may not pose a significant threat to embryos and fetuses.
Iron deficiency anemia 
Coffee consumption can lead to, but is not the cause of iron deficiency anemia, especially in mothers and infants. Coffee also interferes with the absorption of supplemental iron. Interference with iron absorption is due to the polyphenols present in coffee. Four major classes were identified: flavan-3-ols (monomers and procyanidins), hydroxycinnamic acids, flavonols and anthocyanidins.
Coronary artery disease 
A 2004 study tried to discover why the beneficial and detrimental effects of coffee conflict. 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 (24 fl oz or 600 mL) or fewer per day.
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, increases serum cholesterol levels, especially in women. Filtered coffee contains only trace amounts of cafestol.
Polymorphisms in the CYP1A2 gene may lead to a slower metabolism of caffeine. In patients with a slow version of the enzyme the risk for myocardial infarction (heart attack) is increased by a third (2–3 cups) to two thirds (>4 cups). The risk was more marked in people under the age of 59.
A Harvard study conducted over the course of 20 years of 128,000 people published in 2006 concluded that there was no evidence to support the claim that coffee consumption itself increases the risk of coronary heart disease. The study did, however, show a correlation between heavy consumption of coffee and higher degrees of exposure to other coronary heart disease risk factors such as smoking, greater alcohol consumption, and lack of physical exercise. The results apply only to coffee filtered through paper filters, which excludes boiled coffee and espresso, for example. Additionally, the lead researcher on this study acknowledged that subsets of the larger group may be at risk for heart attack when drinking multiple cups of coffee a day due to genetic differences in metabolizing caffeine.
The Iowa Women's Health Study showed that women who consumed coffee actually had fewer cardiovascular disease incidents and lower cancer rates than the general population. For women who drank 6 or more cups, the benefit was even greater. However, this study excluded 35% of its original participants who already had cardiovascular disease and other chronic diseases when the study began. Since participants were all over the age of 55, no good conclusion can be drawn about the long term effect of coffee drinking on heart disease from this study.
Interactions with medications 
Caffeine with Tylenol (Paracetamol, acetaminophen) may damage liver.
A link between heavy coffee drinking and increased risk of glaucoma was found in data from men and women in the Nurses Study and the Health Professionals Follow-up Study.
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