Should you drink coffee? If so, how much? These seem like questions that a society able to create vaccines for a new respiratory virus within a year should have no trouble answering. And yet the scientific literature on coffee illustrates a frustration that readers, not to mention plenty of researchers, have with nutrition studies: The conclusions are always changing, and they frequently contradict one another.
This sort of disagreement might not matter so much if we're talking about foods or drinks that aren't widely consumed. But in 1991, when the World Health Organization classified coffee as a possible carcinogen, the implications were enormous: More than half of the American population drinks coffee daily. A possible link between the beverage and bladder and pancreatic cancers had been uncovered by observational studies. But it would turn out that such studies — in which researchers ask large numbers of people to report information about things like their dietary intake and daily habits and then look for associations with particular health outcomes — hadn't recognized that those who smoke are more likely to drink coffee. It was the smoking that increased their cancer risk; once that association (along with others) was understood, coffee was removed from the list of carcinogens in 2016. The next year, a review of the available evidence, published in The British Medical Journal, found a link between coffee and a lower risk for some cancers, as well as for cardiovascular disease and death from any cause.
Now a new analysis of existing data, published in the American Heart Association journal Circulation: Heart Failure, suggests that two to three (or more) cups of coffee per day may lower the risk of heart failure. Of course, the usual caveats apply: This is association, not causation. It could be that people with heart disease tend to avoid coffee, possibly thinking it will be bad for them. So ... good for you or not good for you, which is it? And if we can't ever tell, what's the point of these studies?
From The New York Times
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