A disclaimer: I do not own stock in Starbucks nor, to my knowledge, in any other company that sells coffee or its accouterments. I last wrote about America's most popular beverage four years ago, and the latest and largest study to date supports that earlier assessment of coffee's health effects.
Although the new research, which involved more than 400,000 people in a 14-year observational study, still cannot prove cause and effect, the findings are consistent with other recent large studies.
The findings were widely reported, but here's the bottom line: When smoking and many other factors known to influence health and longevity were taken into account, coffee drinkers in the study were found to be living somewhat longer than abstainers. Further, the more coffee consumed each day - up to a point, at least - the greater the benefit to longevity.
The observed benefit of coffee drinking was not enormous - a death rate among coffee drinkers that was 10 percent to 15 percent lower than among abstainers. But the findings are certainly reassuring, and given how many Americans drink coffee, the numbers of lives affected may be quite large.
Updating the Evidence
In decades past, experts repeatedly warned that a coffee habit could harm health and shorten lives. And, indeed, the new study did find that when the data were adjusted only for age, the risk of death was greater among coffee drinkers.
But when the researchers took into account other health-related characteristics among the participants, like smoking, alcohol use, meat consumption, physical activity and body mass index, those who regularly drank coffee lived longer.
"Coffee drinkers shouldn't be worried," said Neal Freedman, an epidemiologist at the National Cancer Institute who directed the study. "Their risk is quite similar to that of nondrinkers."
美国国家癌症研究所(National Cancer Institute)的流行病学家尼尔·弗里德曼(Neal Freedman)是这项研究的负责人，他说：“喝咖啡的人大可不必担心，他们的健康风险基本等同于不喝咖啡的人。”
Coffee drinkers who were relatively healthy when the study began were less likely than nondrinkers to die of heart disease, respiratory disease, stroke, diabetes, infections, injuries and accidents.
The study, published in May in The New England Journal of Medicine, examined data on 402,260 adults in the National Institutes of Health-AARP Diet and Health Study. They were ages 50 to 71 and free of heart disease, cancer and stroke when the study began in 1995. By 2008, 52,515 had died. Dr. Freedman and his co-authors examined why they died in relation to how much coffee they said they drank when the study began.
美国卫生研究院-美国退休者协会(NIH-AAPR)合作进行了这项饮食和健康研究，分析了来自402260位成年人参与者的数据，《新英格兰医学杂志》(The New England Journal of Medicine)在今年5月发表了研究报告。研究始于1995年，参与者的年龄介于50至71岁之间，并且都没有患心脏疾病、癌症或中风。到了2008年，其中52515位参与者已经去世。弗里德曼博士和他的合作者分析了参与者的死因与其在研究开始时自诉的喝咖啡量之间的关系。
The risk of death gradually dropped as the number of cups the participants drank increased to four or five. At six cups or more each day, there was a slight rise in death risk, compared with that at four or five cups. But the chances of death remained lower than among people who drank no coffee.
Reflecting practices of the mid-1990s, the researchers considered a cup of coffee to be 8 to 10 ounces. The gargantuan cups now often served would count as more than one cup, Dr. Freedman said. Several of these extra-large cups can cause restlessness, irritability, sleeplessness and anxiety (and might enable me to fly without an airplane).
Contrary to previous belief, at usual levels of consumption, coffee is not any more of a diuretic than the equivalent amount of water. Up to six cups a day can be counted toward one's recommended liquid intake.
Effects on Health
Coffee is a complex substance that contains more than 1,000 compounds that may affect health. Caffeine, a stimulant, is the most studied and sought after. The amounts in coffee can vary greatly, from about 70 milligrams in a shot of espresso to about 100 milligrams in eight ounces of brewed coffee.
But there can be wide variability in caffeine levels, even in similar beverages. As Jane V. Higdon and Balz Frei of Oregon State University reported in Critical Reviews in Food Science and Nutrition, when the same type of coffee was purchased from the same store on six different days, the caffeine content varied from 130 milligrams to 282 milligrams in an eight-ounce cup.
即使是同种咖啡饮料，咖啡因的含量也变化很大。俄勒冈州立大学(Oregon State University)的简·V·希格顿(Jane V. Higdon)和巴尔兹·弗雷(Balz Frei)在《食品科学与营养评论》(Critical Reviews in Food Science and Nutrition)发表的论文中报告称，研究人员分别在六天从同一家咖啡店购买同种类型的咖啡，结果一杯8盎司咖啡的咖啡因含量从130毫克至282毫克不等。
Nor is caffeine is the only compound in coffee important to health. In the new study, little or no difference was found in death rates among those who drank predominantly caffeinated coffee or decaffeinated coffee. Other substances - like antioxidants and polyphenols - probably also play a health-related role, the researchers noted.
Their findings should reassure people concerned about possible harm from substances long used to remove caffeine from coffee. Fear of these chemicals prompted many manufacturers to switch to the Swiss water method for removing caffeine.
But how coffee is brewed can make a health difference. Two prominent chemicals in coffee beans, cafestol and kahweol, are known to raise blood levels of cholesterol and especially artery-damaging LDL cholesterol. These substances are removed when coffee is prepared through a filter, but remain in espresso, French press and boiled coffee. Single-serving coffee pods, like those used in a Keurig, contain filters.
Even though coffee can cause a temporary rise in blood pressure, the new study, like those before it, found the risk of heart disease to be lower among otherwise healthy coffee drinkers. Other benefits suggested by recent studies include a reduced risk of Type 2 diabetes, liver disease and Parkinson's disease. Some research has found a reduced risk of depression, dementia and Alzheimer's disease among coffee drinkers.
People who engage in strenuous physical activities can also benefit, but only if their coffee contains caffeine, which helps muscles use fatty acids for energy and blunts the effect of adenosine, extending the time before muscles fatigue. Post-exercise soreness is also reduced and recovery time shortened.
Whether coffee poses a risk to pregnant women remains controversial. A causal relationship between coffee consumption and miscarriage has not been demonstrated at caffeine intakes of less than 300 milligrams a day, but some studies have found increased risk of low birth weight associated with consuming more than 150 milligrams a day.
Keep in mind, too, that caffeine is a drug. Some medications, including Tagamet, Diflucan, Luvox, Mexitil, estrogens and antibiotics like Cipro and Levaquin, interfere with the metabolism of caffeine and can increase its effects.
In other cases, caffeine can enhance the effect of drugs like aspirin and acetaminophen (a benefit for pain relief). Caffeine can be toxic if used with prescribed doses of the antipsychotic medication clozapine.