How reading about coffee may harm your health*

Or perhaps we’re grossly exaggerating...

dongga BS/Flickr

If you scanned yesterday’s headlines while sipping your morning coffee, you must have felt smug about your choice of beverage. A new prospective study, published in the New England Journal of Medicine, found that there seems to be an “inverse association between coffee drinking and total and cause-specific mortality.” In other words, scientists looked at individuals over time and noticed an association between drinking coffee and a longer life.

Now, because of the nature of this “observational study”—where no intervention is introduced, where subjects aren’t randomized, where researchers just look at the link between an exposure to something and a certain outcome—the authors of the article were careful to acknowledge that, “Whether this was a causal or associational finding cannot be determined from our data.”

Yet, this brief but crucial note seemed to be lost in some of the reporting on the subject or referenced only several paragraphs after hyperbolic headlines and opening sentences.

Inspired by the great review of U.S. coverage by Gary Schwitzer, Science-ish looked at how the big coffee study was packaged—headline and leading paragraphs—in our nation’s newspapers:

From the Vancouver Sun: “Coffee drinkers live longer, big study finds”

“One of life’s simple pleasures just got a little sweeter. After years of waffling research on coffee and health, even some fear that java might raise the risk of heart disease, a big study finds the opposite: Coffee drinkers are a little more likely to live longer. Regular or decaf doesn’t matter.”

From the CBC: “Coffee drinkers reassured about health risks”

“Coffee drinkers can be reassured about the health risks of enjoying their cup of java, doctors say.
In a study of more than 402,000 men and women aged 50 to 71 in the U.S., researchers looked at the association between coffee consumption and mortality.”

From the Winnipeg Free Press: “Pour it on: Drinkers of coffee – regular or decaf – live longer, big federal study finds”

“Coffee seems to be good for you. Or at least it’s not bad, say researchers who led the largest-ever study of coffee and health.
They found that coffee drinkers seemed a little more likely to live longer than folks who drink no coffee at all. Regular or decaf didn’t matter.”

From the Toronto Star: “Coffee may help you live longer, study suggests”

“Coffee, caffeinated or decaffeinated, may help extend the lives of people who drink it daily, a U.S. study found.
Men who drank 2 to 3 cups a day had a 10 per cent chance of outliving those who drank no coffee, while women had a 13 per cent advantage, according to research published Wednesday in the New England Journal of Medicine.”

South of the border, even the New York Times, which usually does a good job of reporting science in context, framed the study this way: “Coffee Drinkers May Live Longer”

“Your morning cup of coffee may start to taste even better after a major government study found that frequent coffee drinkers have a lower risk of dying from a variety of diseases, compared with people who drink little or no coffee.”

While sensational packaging may attract our quick clicks online, it’s important to scrutinize the reporting and beware oversold write-ups on observational data. You’ll come across it every day, as in: “Eating lots of chocolate helps people stay thin, study finds” or “More coffee may equal less depression in women.”

That’s not to say that observational studies are not valuable. They are. Observational data about tobacco gave way to the realization that smoking is linked to lung cancer and that thalidomide—the drug pregnant women used to combat morning sickness—causes birth defects and nerve-system damage. This was information a trial would have taken years to uncover or territory scientists would never wade into. (Ie. It would be unethical to ask people to take up smoking or go on a drug we suspect is potentially deadly for the purposes of a study.)

But this kind of science has its limits. With observational studies—as opposed to controlled experiments where interventions are introduced—scientists look at phenomena “out there.” All they can show is an association between two factors, such as coffee and mortality, not that one factor caused the other, or vice versa.

Of the coffee study, Steven Hoffman, assistant professor at McMaster University, said, “Yes, if the coffee group tends to live longer than the non-coffee group, that is suggestive that coffee may possibly have a protective effect. But there may be factors that are associated with both coffee and a longer life. For example, higher income earners may be more likely to drink coffee and live longer.” This is known as a “confounding factor.” Of course, scientists can control for possible confounders, and they did in the new coffee study. “But we can’t control for those factors that we didn’t think to control for or factors that are unobservable,” Hoffman added. “Maybe happier people tend to drink more coffee and tend to live longer for reasons unrelated to their proclivity for coffee.”

Still, no matter how many dedicated debunkers cry out about the “Chocolate/avocados/apples/kale will make you thinner/live longer/healthier/sexier” school of health reporting, it’s here to stay. We love a quick fix, after all, and a sexy headline. Just be sure to add a spoonful of skepticism to your immortality brew tomorrow.

*Today’s headline is intentionally hyperbolic.

Science-ish is a joint project of Maclean’s, the Medical Post and the McMaster Health Forum. Julia Belluz is the associate editor at the Medical Post. Got a tip? Seen something that’s Science-ish? Message her at or on Twitter @juliaoftoronto

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