Coffee drinkers are less likely to die than decaffeinated abstainers, according to two new studies published today in Annals of Internal Medicine. The first study, which involved 520,000 Europeans, found that those who drank three or more cups of coffee per day had the lowest death rates. The second study, which involved 185,000 whites and minorities in the U.S., reported similar results. The implication, a thousand ill-conceived news stories have claimed, is that the only thing standing between you and ripe old age is a cup of joe.
Not so.We’re not buying it and neither is Eliseo Guallar, an epidemiologist and human nutrition expert at Johns Hopkins University in Baltimore.
“Coffee intake is a complex behavior, coffee itself is a heterogeneous exposure, and the putative benefits may depend on components other than caffeine,” Guallar wrote in the Annals of Internal Medicine, providing a very needed and predictably overlooked caveat. “Recommending coffee intake to reduce mortality or prevent chronic disease would be premature.”
Premature might be an understatement give that, some 3,000-plus studies later, the one statement about coffee we know to be true is that it cures both everything and nothing. Seriously. Skin cancer. Colon cancer. Breast cancer. Prostate cancer. Alzheimer’s and diabetes. Not to mention coffee’s purported ability to lower risk of heart attack. Weird that everyone isn’t living longer. Also, interesting that coffee has been shown to trigger heart attacks. And cause cancer. And shorten lifespans.
During a single month in 2015, we saw no less than three shifts in the link between coffee and diabetes. First, it was a core cause of Type II diabetes. Then, there was no relationship between coffee and diabetes whatsoever. And finally—you guessed it—scientists found it prevented diabetes.
Long story short: Coffee is complicated and not a panacea. Long story shorter: Don’t trust good news.
To be fair, dietary research is hard. After a spate of melanoma-coffee studies spilled into the news cycle in 2015, Yale University internist Perry Wilson explained that we’ll probably never really know whether coffee cures or causes any disease.
“Is it possible that coffee reduces the rate of melanoma?” he asked. “Sure. There are about 100 different compounds in coffee, and some of them may be beneficial. Of course, some of those compounds might cause cancers as well. And that’s one of the central problems of dietary research. The exposures are so broad that one can justify almost any preconceived hypothesis based on preliminary data.”
Guallar echoes these concerns in his editorial. After noting that it is nigh impossible to figure out how much coffee study participants are drinking—even if we assume people keep reasonably good tabs on their coffee intake, there is wide variation in the amount of caffeine in different types of coffee—Guallar adds that coffee contains several bioactive substances. Polyphenols, diterpenes, and melanoidins all exist in coffee at unpredictable levels and, as soon as you add sugar or cream to the mix, the plot thickens. No two cups of coffee are similar enough to study.
Guallar does allow that there may be healthy substances in coffee, such as antioxidants. But the data from these two new studies is less than convincing. “The association of coffee intake with mortality,” Guallar writes. “Was modest and sensitive to confounding.” Perhaps the sort of person who can afford three cups of coffee per day can also afford health care. Perhaps coffee drinkers tend to be healthier to begin with. Perhaps they’re more likely to go to the gym.
Until true control and experimental groups exist–and good luck with that–consider all coffee research preliminary. Except for those studies that suggest coffee increases happiness and lowers risk of suicide and depression. That sounds about right.