Scientific studies have examined the relationship between coffee consumption and an array of medical conditions. Findings have been contradictory as to whether coffee has any specific health benefits, and results are similarly conflicting regarding the potentially harmful effects of coffee consumption. Variations in findings, however, can be at least partially resolved by considering the method of preparation. Coffee prepared using paper filters removes oily components called diterpenes that are present in unfiltered coffee. Two types of diterpenes are present in coffee: kahweol and cafestol, both of which have been associated with increased risk of coronary heart disease via elevation of low-density lipoprotein (LDL) levels in blood. Metal filters, on the other hand, do not remove the oily components of coffee.
Coffee consumption has been shown to have minimal or no impact, positive or negative, on cancer development; 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." Other studies suggest coffee consumption reduces the risk of being affected by Alzheimer's disease, Parkinson's disease, heart disease, diabetes mellitus type 2, cirrhosis of the liver, and gout. A longitudinal study in 2009 showed that those who consumed a moderate amount of coffee or tea (3–5 cups per day) at midlife were less likely to develop dementia and Alzheimer's disease in late-life compared with those who drank little coffee or avoided it altogether. It increases the risk of acid reflux and associated diseases. Most of coffee's beneficial effects against type 2 diabetes are not due to its caffeine content, as the positive effects of consumption are greater in those who drink decaffeinated coffee. The presence of antioxidants in coffee has been shown to prevent free radicals from causing cell damage. A recent study showed that roast coffee, high in lipophilic antioxidants and chlorogenic acid lactones, protected primary neuronal cell cultures against hydrogen peroxide-induced cell death.
In a healthy liver, caffeine is mostly broken down by the hepatic microsomal enzymatic system. The resulting metabolites are mostly paraxanthines—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 most elderly people. Excessive amounts of coffee, however, can, in many individuals, cause very unpleasant, exceptionally even life-threatening adverse effects.
Coffee consumption can lead to iron deficiency anemia 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. Although the inhibition of iron absorption can cause an iron deficiency, iron is considered a carcinogen in relation to the liver. Polyphenols contained in coffee are therefore associated with decreasing the risk of liver cancer development.
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.
Over 1,000 chemicals have been reported in roasted coffee; more than half of those tested (19/28) are rodent carcinogens. Coffee's negative health effects are often blamed on its caffeine content. Instant coffee has a much greater amount of acrylamide than brewed coffee. Research suggests that drinking caffeinated coffee can cause a temporary increase in the stiffening of arterial walls. Caffeinated coffee is not recommended for everybody. It may aggravate preexisting conditions such as gastroesophageal reflux disease, migraines, arrhythmias, and cause sleep disturbances.
Coffee is no longer thought to be a risk factor for coronary heart disease. One study suggests 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. Caffeine has been associated with its ability to act as an antidepressant. A review by de Paulis and Martin indicated a link between a decrease in suicide rates and coffee consumption, and suggested that the action of caffeine in blocking the inhibitory effects of adenosine on dopamine nerves in the brain reduced feelings of depression. A 1992 study concluded that about 10% of people with a moderate daily intake (235 mg per day) experienced increased depression and anxiety when caffeine was withdrawn, but a 2002 review of the literature criticised its methodology and concluded that "the effects of caffeine withdrawal are still controversial. About 15% of the U.S. general population report having stopped drinking coffee altogether, citing concern about health and unpleasant side effects of caffeine.
CAFFEINE AND HEADACHES
There is some controversy over whether the caffeine in coffee causes headaches or helps relieve headaches. In a 2000 controlled study by the Diamond Headache Clinic in Chicago, Illinois, revealed that adults who took ibuprofen, an over the counter pain killer, combined with caffeine or one cup of coffee had increased effectiveness against tension headaches. The study did not recommend that the caffeine and ibuprofen combination was effective against migraine headaches. A Johns Hopkins controlled study has linked drinking coffee with addictive withdrawal headaches, even with those who drink coffee in moderation. A 2009 Norwegian University of Science and Technology controlled study claims that heavy coffee drinkers, four cups a day, are more likely to suffer occasional headaches than persons who have low coffee or caffeine consumption.
CAFFEINE CONTENT
The stimulant effect of coffee is due to its caffeine content. The caffeine content of a cup of coffee varies depending mainly on the brewing method, and also on the variety of bean.Coffee has the following caffeine content:
- Brewed: 1 cup (7 oz, 207 ml) = 80–135 mg.
- Drip: 1 cup (7 oz, 207 ml) = 115–175 mg.
- Espresso: 1 shot (1.5–2 oz, 45–60 ml) = 100 mg
Positive effects
☺ High long-term consumption is associated with a lower risk of cardiovascular disease and diabetes.
☺ Research is beginning to suggest that caffeine minimizes the cognitive decline associated with aging.
☺ Caffeine increases levels of neurotransmitters such as noradrenaline, acetylcholine, and dopamine.
☺ Acetylcholine is associated with attention, concentration, learning, and memory but there is no conclusive evidence yet that caffeine has any effect on memory and cognitive function.
☺ Low doses of caffeine show increased alertness and decreased fatigue.
☺ Caffeine has been shown to increase the metabolic rate.
☺ Caffeine may reduce the risk of developing cancer and produce a delay in the average onset of cancer.
☺ Caffeine may be associated with a reduced risk of Parkinson’s disease.
☺ Caffeine may lower the risk of developing type 2 diabetes.
☺ Caffeine may reduce certain kind of hepatic cancers.
In these studies, the greatest benefits were observed in those who drank coffee for a long period in their lifetime.
Negative effects
☻ Caffeine can increase vasoconstriction and blood pressure.
☻ High blood pressure is associated with an increase in strokes, and cerebral vascular disease, which in turn increase the risk of multi-infarct dementia.
☻ Caffeine may reduce control of fine motor movements (e.g., producing shaky hands)
☻ Caffeine can stimulate urination.
☻ High doses of caffeine can cause anxiety.
☻ Caffeine can contribute to increased insomnia and sleep latency.
☻ Caffeine withdrawal produces headache, fatigue and decreased alertness.
☻ Caffeine may be addictive.
CONSUMPTION RECOMMENDATIONS
Adults
Health Canada has not developed definitive advice for adolescents 13 and older because of insufficient data. Nonetheless, Health Canada suggests that daily caffeine intake for this age group be no more than 2.5 mg/kg body weight. This is because the maximum adult caffeine dose may not be appropriate for light weight adolescents or for younger adolescents who are still growing. The daily dose of 2.5 mg/kg body weight would not cause adverse health effects in the majority of adolescent caffeine consumers. This is a conservative suggestion since older and heavier weight adolescents may be able to consume adult doses of caffeine without suffering adverse effects. For the rest of the general population of healthy adults, Health Canada advises a daily intake of no more than 400 mg.
According to the US-based Waverly Health Center, three 8 oz cups of coffee (about 250 milligrams of caffeine) per day is considered an average or moderate amount of caffeine; ten 8 oz cups of coffee per day is considered an excessive intake of caffeine.
Pregnant women
For women of childbearing age, Health Canada recommends a maximum daily caffeine intake of no more than 300 mg, or a little over two 8 oz (237 mL) cups of coffee.
Children
For children age 12 and under, Health Canada recommends a maximum daily caffeine intake of no more than 2.5 milligrams per kilogram of body weight. Based on average body weights of children, this translates to the following age-based intake limits:
Age range | Maximum recommended daily caffeine intake: |
4-6 | 45 mg |
7-9 | 62.5 mg |
10-12 | 85 mg |
Relatedly, one study found that caffeine can be used to treat hyperkinetic children. The research showed 200–300 mg of caffeine has a similar effect to methylphenidate in treating hyperkinetic impulse disorder. Moreover, the caffeine treatment did not show the side-effects caused by methylphenidate.
