A venti-sized serving of misinformation in news stories on latest coffee study

If you want to get a sense of how tired readers are of the latest round of headlines pondering the health benefits (or risks) of coffee, then all you need to do is read the replies on this tweet:

Coffee is good for you, more science shows. https://t.co/YiZ7yOfItw

— NBC News (@NBCNews) July 2, 2018

As a Twitter user named Mark Richardson replied, “I guarantee you that in 6 months it will be bad for you again.”

And user Rachel Lee said: “Last year you said research showed coffee leads to cancer. Now theres another research saying coffee is good? Which is it?”

And, last but not least, a user calling herself AintNoSpringChicken: “Correlation is not causation. But hey. Coffee addicts like me could be tempted to take this at face value!”

About that ‘correlation is not causation’

To find out why, please see our page Observational studies: Does the language fit the evidence?

Spring Chicken is right — the study wasn’t designed to prove that coffee will help you live longer.

It was an observational trial, albeit a large one, that used about half a million records from people who donated tissue and samples to the UK BioBank. Researchers found a slightly lower risk of death over 10 years of follow-up among people who self-reported that they drink coffee.

The researchers said their study “should be interpreted with caution.” They didn’t claim a health benefit, but rather said the findings “provide further evidence that coffee drinking can be part of a healthy diet and may provide reassurance to those who drink coffee and enjoy it.”

Yet, predictably, the news stories we saw not just told readers that “coffee drinkers are more likely to live longer” (NPR’s headline), they often told readers to “go ahead and have another cup” as the AP advised in its opening sentence.

“The title and first few sentences of both media articles are inaccurate and misleading,” said Noah Haber, ScD, a postdoctoral researcher at the Carolina Population Center at the University of North Carolina at Chapel Hill. “The study does not show that it ‘may boost chances for a longer life,’ ‘suggest a benefit,’ or show a ‘longevity boost.’ At best, the study does not eliminate the plausible hypothesis that coffee positively impacts longevity, but it also does not eliminate the hypotheses that coffee negatively impacts longevity, or that it has no meaningful impact.”

It’s complicated

It’s no wonder readers are feeling snarky and fatigued, since not too long ago, we were being told coffee is probably harmful.

“For instance, people who drink coffee may do so because they wake up early to go to their place of work. Since people with jobs tend to be in a better state of health than those who don’t have jobs, the association between coffee and survival may in fact be simply due to the fact that coffee drinkers are healthy enough to work,” explained Alexander Breskin, PhD, a postdoctoral researcher in epidemiology, also at UNC-Chapel Hill.

Haber noted that by including various theories like these “it gives implicit weight to the initial assumption of a causal effect.”

Yet, as we discussed earlier, “the study doesn’t actually show that it does have a positive impact.”

At least things like inflammation and liver function are potentially measurable. My favorite bit o’ speculation was this dreamy quote in the NPR story:

Gardner says part of the benefit of coffee may be linked to something profoundly simple: It brings people joy.

“Think about when you’re drinking coffee — aren’t you stopping and relaxing a little bit?” Gardner asks.

Clearly he hasn’t grappled with my reason for drinking coffee, which is my five-year-old daughter at 7:30 in the morning.