Can drinking coffee really help you live longer? New study is hardly conclusive

Pat Greenhouse/Globe Staff
Pat Greenhouse/Globe Staff

Have you been to Starbucks yet today? Even if you’re not a coffee drinker, you may have been tempted to grab a cup of java this morning after hearing the news that drinking coffee may help you live longer. The study—conducted by government researchers (with no funding from the coffee industry) and published in the prestigious New England Journal of Medicine—found a small association between drinking coffee and a longer lifespan.

Going for that extra cup of coffee based on this study finding, however, would be a foolish thing to do since an outside expert, the journal’s editor, and the study investigator all told me they didn’t believe the modest finding should push Americans to drink even more coffee than they already do.

While the research was the largest coffee study to date—involving more than 400,000 American adults—and funded by the National Institutes of Health, it doesn’t prove that coffee actually helps us live longer, nor did it even find a strong statistical association. What the researchers found was that men who drank two or more cups of coffee a day had about a 10 percent lower risk of dying over a 13-year period compared with those who drank none; those who drank one cup had a 6 percent lower risk.

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Women had a somewhat greater benefit: about a 15 percent lower risk of dying if they drank at least two daily cups of coffee.

The latest finding builds on a string of other studies finding similar beneficial associations from coffee such as protection against diabetes, lowered stroke risk, and less depression. Coffee has even been dubbed a cancer-fighting food. But beyond small clinical trials to assess the effects of coffee on certain blood biomarkers, no one has studied whether folks randomly assigned to drink coffee are healthier or live longer than those who drink a placebo that they think is coffee.

(Of course, that study would be tough if not impossible to conduct.)

“It’s important to interpret this finding cautiously,” said study author Neal Freedman, an investigator at the National Cancer Institute. “It may provide reassurance to those drinking coffee that coffee doesn’t increase their risk of death overall. but whether it really reduces death? We can’t say that for certain.”

That being the case, I wondered why this study was published at all and, no less, in one of the world’s leading medical journals.

“I’m not a fan in general of epidemiological studies of this type because they can be confounded by variables,” Dr. Jeffrey M. Drazen, editor-in-chief of the New England Journal of Medicine, told me in an interview. While the researchers took into account more than a dozen differences (such as smoking rates, body weight, education level) that distinguished heavy coffee drinkers from those that abstained, Drazen said they couldn’t account for everything.

For instance, the survey on which the results were based didn’t ask participants whether they had health insurance or had high blood pressure or high cholesterol levels—all of which could factor into their expected lifespan. It also looked at coffee drinking habits only at one point in time, and people may change their consumption over the years.

Drazen said that there was some disagreement among the journal’s editorial board about whether to publish this study but added that he’s often more inclined to publish a study “if it touches a nerve” because it’s important to stimulate discussion in the community at large. “We went into this fully realizing the strengths and weaknesses of the study,” he added. “I think the authors were very cautious in their interpretation.”

But one of the country’s leading medical researchers, Dr. Steven Nissen, chair of cardiovascular medicine at the Cleveland Clinic, said the study is apt to be misinterpreted by the public at large. Many may assume from the findings—and headlines such as “coffee drinkers live longer”—that all they need to do is drink coffee if they want to erase the effects of bad health habits such as smoking.

In fact, those who smoked and drank the most coffee had a greater risk of dying earlier in the study than those who didn’t smoke or drink coffee.

“People who drink a lot coffee are very different from those who don’t,” Nissen said. They smoke more, have a lower level of education, exercise less, and eat more red meat, according to this study and previous ones. “Any time you try to adjust for all these factors, the adjustment is likely to be inaccurate and incomplete—and this one in the study is particularly bad.”

What everyone can agree on: People shouldn’t alter their coffee-drinking habits based on the findings of this study. “You shouldn’t feel good about drinking coffee or bad about it,” said Drazen. “Any effect it has is small.”