Produced from ground beans of the coffee plant, coffee actually contains more than 1000 different plant-derived chemical components. Polyphenols are one family of plant compounds that are abundant in coffee as well as red wine, fruits and fruit juices, tea, vegetables, chocolate and legumes. The properties of polyphenols have only been under investigation since the 1990s, but there is increasing evidence that they contribute to many aspects of our overall health.
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Polyphenols are a rich source of dietary antioxidants. On average, people consume about 10 times more polyphenols than they do vitamin C. Coffee contains a type of polyphenol called chlorogenic acids, which are esters of quinic and cinnamic acids. 5-O-caffeoylquinic acid is the most abundant polyphenol present in coffee. Laboratory studies have shown that this compound has potent antioxidant activity. It is not yet known whether this antioxidant activity has any benefits for disease. In animals, chlorogenic acid reduces the incidence of liver cancer and colorectal cancer. More studies are needed to determine whether these findings also apply to humans.
Several prospective studies have found that coffee reduces the risk of Type 2 diabetes. This effect has been observed with decaffeinated coffee as well, indicating that other active substances in the coffee are responsible. One candidate is trigonelline, a nicotinic acid in coffee that lowers blood sugar in animal studies.
It has been difficult to study the effect of specific compounds in coffee on cholesterol because epidemiological studies may not control for other lifestyle factors such as smoking and diet. A series of experiments reported in the scientific journal "Circulation Research" focuses on two polyphenols in coffee, caffeic and ferulic acids. The researchers show that these two compounds reduce cholesterol levels. They act by aiding the transport of from macrophage foam cells to the liver, where it is processed for excretion.
Although the polyphenols in coffee have many potential health benefits, excessive coffee consumption is linked to health risks. Coffee contains approximately 100 mg of caffeine in each small cup. A moderate amount of caffeine, less than 300 mg per day, is well tolerated by most people. Higher amounts may contribute to increased blood pressure, anxiety, insomnia and osteoporosis. Pregnant women should limit caffeine consumption to less than 300 mg per day.