Older adults who consume three cups of coffee or more daily might lower their risk of dying from common causes by 10%, compared with those who drink no coffee, a large US National Cancer Institute study suggests.
The finding applies to 50- to 71-year-olds drinking either caffeinated or decaffeinated coffee. And it suggests that coffee drinking is associated with a dip in fatalities stemming from cardiovascular disease, respiratory illness, stroke, diabetes, infections, and injuries and accidents.
But the team stressed that it remains unclear in what way coffee might confer a health benefit, and that the study did not establish any cause-and-effect relationship.
How much coffee people drink
"I think it's really important to point out that our study was observational," said study lead author Neal Freedman, an investigator with the division of cancer epidemiology and genetics at the US National Cancer Institute in Rockville.
"That means that we simply asked people how much coffee they drink and followed them," he said. "But coffee drinking is just one of the many things people do. Coffee is associated with many different behaviours. So we don't know what else might be affecting this association."
For instance, coffee drinkers tend to smoke more, which is a major cause of death, Freedman noted. "And so when we first looked at the association, we found that coffee drinkers actually faced a higher risk of death, and it was only when we discounted smoking that we found the reverse relationship."
The study is published in the New England Journal of Medicine.
How the study was done
For the study, the investigators focused on the dietary habits of about 400 000 men and women enrolled in the National Institutes of Health-AARP Diet and Health Study between 1995 and 1996. None of the participants had a history of cancer, stroke or heart disease when the study started.
Each participant was questioned about their coffee consumption, ranging from zero to a maximum category of six cups a day or more. The health of each was tracked through 2008 or until death.
The results showed that drinking even one cup of coffee a day was linked to a lower overall risk of dying and a lower specific risk of dying from many of today's most potent public health concerns.
The notable exception: Coffee drinking was not linked to a reduction in cancer fatalities among women, and had only a marginal protective impact on cancer deaths among men.
The protective effect appeared greater among those who drank more than one cup a day, although Freedman noted that little difference was seen between the apparent benefit at two cups a day and six cups a day.
Preparation of coffee important
"And going forward we really need to look at the many different components in coffee," he added. "Besides caffeine, coffee contains about another 1,000 compounds and antioxidants, some of which may be beneficial and some not."
Coffee preparation also needs to be explored, Freedman noted. "Because a lot of people like drip coffee, but others have espresso or French press. And the beans can be roasted to different amounts. And each of these choices affects the compound. And we don't know whether this affects the association with disease as well," he explained.
The authors cautioned that participants were not asked if their coffee-drinking habits had changed over the study period. Also, the study did not take into account pre-existing health issues.
For now, Freedman recommends talking to your doctor before starting to drink more coffee because personal health history might affect the advice you receive.
Lona Sandon, a registered dietitian and assistant professor of clinical nutrition at the University of Texas Southwestern Medical Center at Dallas, said that, at a minimum, the new study seems to confirm what most research to date has suggested: that coffee drinking is not bad for you.
"Now this study is going beyond that to suggest that it might actually be helpful," Sandon added. "But what is the connection? We don't know yet."
Whether it's the caffeine, the beneficial antioxidants and phytochemicals found in coffee beans or simply something lifestyle-related remains to be seen, she said.