People on 2.5 to 3.5 cups a day died less often than non-drinkers
Across 40 studies and nearly 3.9 million people, deaths overall ran 11 to 18% lower than in non-drinkers. Nobody was assigned to drink coffee, so the habit may not be the cause.
What the study found
Around 2.5 to 3.5 cups a day tracked with 11 to 18% fewer deaths
Across 40 studies and nearly 3.9 million people, those drinking about 2.5 to 3.5 cups of coffee a day died less often than non-drinkers, by 11 to 18% for deaths overall and for heart deaths. Past that the line flattens: a fourth and a fifth cup added nothing.
The caveat · Diet, smoking and income ride along
Nobody was assigned to drink coffee, so whatever else separates a three-cup habit from none, in diet, smoking, exercise or income, is folded into that number. Coffee carries hundreds of compounds besides caffeine, and nothing here tells them apart. The size of the association differed by region, running stronger in Europe and Asia than in the US.
What we don't know
That coffee drinkers die less often is not in doubt; whether anything in the cup causes it is. Nobody was assigned to drink coffee, and nothing separates caffeine from the hundreds of other compounds in it.