In a study of nearly half a million British adults, coffee drinkers had a slightly lower risk of death over 10 years than abstainers.
The apparent longevity boost was seen with instant, ground and decaffeinated, results that echo U.S. research. It's the first large study to suggest a benefit even in people with genetic glitches affecting how their bodies use caffeine.
Overall, coffee drinkers were about 10 percent to 15 percent less likely to die than abstainers during a decade of follow-up. Differences by amount of coffee consumed and genetic variations were minimal.
The results don't prove your coffeepot is a fountain of youth, nor are they a reason for abstainers to start drinking coffee, said Alice Lichtenstein, a Tufts University nutrition expert who was not involved in the research. But she said the results reinforce previous research and add additional reassurance for coffee drinkers.
"It's hard to believe that something we enjoy so much could be good for us — or at least not be bad," Lichtenstein said.
The study was published Monday in the journal JAMA Internal Medicine.
It's not clear exactly how drinking coffee might affect longevity. Lead author Erikka Loftfield, a researcher at the U.S. National Cancer Institute, said coffee contains more than 1,000 chemical compounds, including antioxidants, which help protect cells from damage.
Other studies have suggested that substances in coffee may reduce inflammation and improve how the body uses insulin, which can reduce chances for developing diabetes. Loftfield said efforts to explain the potential longevity benefit are continuing.
For the study, researchers invited 9 million British adults to take part; 498,134 women and men ages 40 to 69 agreed. The low participation rate means those involved may have been healthier than the general U.K. population, the researchers said.
Participants filled out questionnaires about daily coffee consumption, exercise and other habits and received physical exams, including blood tests. Most were coffee drinkers; 154,000, or almost one-third, drank two to three cups daily, and 10,000 drank at least eight cups daily. During the next decade, 14,225 participants died, mostly of cancer or heart disease.
Caffeine can cause short-term increases in blood pressure, and some smaller studies have suggested that it might be linked with high blood pressure, especially in people with a genetic variation that causes them to metabolize caffeine slowly.
But coffee drinkers in the U.K. study didn't have higher risks than nondrinkers of dying from heart disease and other blood pressure–related causes. And when all causes of death were combined, even slow caffeine metabolizers had a longevity boost.