Coffee is not usually thought of as health food, but a number of recent studies suggest that it can be a highly beneficial drink. Researchers have found strong evidence that coffee reduces the risk of several serious ailments, including diabetes, heart disease andcirrhosis of the liver.
Among them is a systematic review of studies published last year in The Journal of the American Medical Association, which concluded that habitual coffee consumption was consistently associated with a lower risk of Type 2 diabetes. Exactly why is not known, but the authors offered several explanations.
Coffee contains antioxidants that help control the cell damage that can contribute to the development of the disease. It is also a source of chlorogenic acid, which has been shown in animal experiments to reduce glucose concentrations.
Caffeine, perhaps coffee's most famous component, seems to have little to do with it; studies that looked at decaffeinated coffee alone found the same degree of risk reduction.
Larger quantities of coffee seem to be especially helpful in diabetes prevention. In a report that combined statistical data from many studies, researchers found that people who drank four to six cups of coffee a day had a 28 percent reduced risk compared with people who drank two or fewer. Those who drank more than six had a 35 percent risk reduction.
Some studies show that cardiovascular risk also decreases with coffee consumption. Using data on more than 27,000 women ages 55 to 69 in the Iowa Women's Health Study who were followed for 15 years, Norwegian researchers found that women who drank one to three cups a day reduced their risk of cardiovascular disease by 24 percent compared with those drinking no coffee at all.
But as the quantity increased, the benefit decreased. At more than six cups a day, the risk was not significantly reduced. Still, after controlling for age, smoking and alcohol consumption, women who drank one to five cups a day - caffeinated or decaffeinated - reduced their risk of death from all causes during the study by 15 to 19 percent compared with those who drank none.
The findings, which appeared in May in The American Journal of Clinical Nutrition, suggest that antioxidants in coffee may dampen inflammation, reducing the risk of disorders related to it, like cardiovascular disease. Several compounds in coffee may contribute to its antioxidant capacity, including phenols, volatile aroma compounds and oxazoles that are efficiently absorbed.
In another analysis, published in July in the same journal, researchers found that a typical serving of coffee contains more antioxidants than typical servings of grape juice, blueberries, raspberries and oranges.
"We were surprised to learn that coffee quantitatively is the major contributor of antioxidants in the diet both in Norway and in the U.S.A.," said Rune Blomhoff, the senior author of both studies and a professor of nutrition at the University of Oslo.
These same anti-inflammatory properties may explain why coffee appears to decrease the risk of alcohol-related cirrhosis and liver cancer. This effect was first observed in 1992. Recent studies, published in June in The Archives of Internal Medicine, confirmed the finding.
Still, some experts believe that coffee drinking, and particularly caffeine consumption, can have negative health consequences. A study published in January in The Journal of the American College of Cardiology, for example, suggests that the amount of caffeine in two cups of coffee significantly decreases blood flow to the heart, particularly during exercise at high altitude.
Rob van Dam, a Harvard scientist and the lead author of The Journal of the American Medical Association review, acknowledged that caffeine could increase blood pressure and slightly increase levels of the amino acid homocysteine, possibly raising the risk for heart disease.
"I wouldn't advise people to increase their consumption of coffee in order to lower their risk of disease," Dr. van Dam said, "but the evidence is that for most people without specific conditions, coffee is not detrimental to health. If people enjoy drinking it, it's comforting to know that they don't have to be afraid of negative health effects."
chlorogenic acid: 绿原酸
glucose concentration: 葡萄糖浓度