Coffee lovers rejoiced this week as media outlets around the world pounced on a news release headline from the BMJ (British Medical Journal) that declared, "Moderate coffee drinking 'more likely to benefit health than to harm it,' say experts."
It's just the latest in a parade of often-contradictory studies over many years about the health effects of that cup of java — some claiming coffee is good for you, some claiming it can be harmful. In this case, the study went so far as to suggest that drinking three cups a day was associated with lower risks of heart disease, diabetes and some types of cancers.
But the researchers themselves acknowledged that the data was mostly observational, and essentially concluded that it was likely safe — except for pregnant women and people at risk of fractures — to proceed to clinical trials to get more definitive answers.
So what does this widely covered study really add to our understanding about coffee and its health effects?
Nothing, according to two nutritional scientists at the University of Toronto.
"It is useless," Ahmed El-Sohemy, who specializes in research about genetics and metabolism, and has conducted several studies on coffee, said bluntly.
That's because these types of studies rely on analyzing data taken from large populations of people and looking for correlations — such as whether or not people who reported drinking coffee also developed heart disease or diabetes or liver disease or whatever it is the researchers are looking for.
But, as anyone who has taken a basic statistics course knows, "correlation is not causation," said Richard Bazinet, an associate professor in U of T's department of nutritional science.
"We look at these population-type studies where we say, 'Ah! People who drink two coffees a day, what's their health like?'" Bazinet said. "These correlations show up, and then when you change the population a bit, they disappear, probably because often they're not real effects."
In the end, El-Sohemy said, the focus needs to shift away from these large population-based studies and attempts to come up with a one-size-fits-all recommendation toward an approach that acknowledges coffee's health effects can vary by individual.
So enjoy your cup of coffee but work on having a healthy lifestyle.
Originally published in CBC.