In an ideal world, the chocolate we eat would have beneficial effects on our health. But for now, unfortunately, that remains in the realm of ‘we don’t really know.’ This is why critics have come out against the reporting of a recent study that linked a higher intake of chocolate with a lower risk of heart disease and stroke. The claims made in the media don't seem to reflect the evidence in the paper, either.
The study, published in the BMJ journal Heart, looked at the eating habits of more than 20,000 individuals involved in the EPIC-Norfolk study. Researchers found that people who admitted to eating a moderate amount of chocolate had a lesser risk of suffering from cardiovascular disease (CVD) and stroke than people who didn’t. This was an observational study, and as Buzzfeed’s Tom Chivers points out, “It’s not clear whether the chocolate is protecting them, or whether people who are at less risk tend to eat chocolate, or whether people aren’t very good at remembering what they’ve eaten. Or something else entirely.”
The Science Media Centre suggests that it was this first line in the statement—“eating up to 100g of chocolate every day is linked to lowered heart disease and stroke risk,” that led “people to infer that chocolate has a protective effect against CVD.” But, as the media watchdog notes, both the paper and the rest of the press release are clear about the limitations of the study, pointing out the problem of recall bias with questionnaires and explicitly stating that “no definitive conclusions about cause and effect can be drawn.” Robbie Gonzalez from io9 explained that it’s rare for a press release to highlight the limitations of its study and that it actually does an “uncharacteristically good job.”
“It includes explicit warnings about causation versus correlation, the unreliability of food questionnaires, and even reverse causation! A recent survey of observational studies found that these sorts of limitations are rarely addressed in press releases and associated news stories,” he added.
Why then were headlines like “Two bars of chocolate a day lowers risk of stroke and heart disease” used? When it comes to indulgences like chocolate, we want to hear we can eat them without any health consequences, or even better, that they come with health benefits. This is best illustrated with a journalist who was able to fool news organizations into believing his bogus study that chocolate helped with weight loss. While the present study had “well conducted observational research,” it still cannot show a causal affect.
There is some good news from the research. As Dr. Tim Chico, reader in Cardiovascular Medicine and consultant cardiologist at the University of Sheffield, said: “The message I take from this study is that if you are a healthy weight, then eating chocolate (in moderation) does not detectibly increase risk of heart disease.”
However, Chico does warn: “I would not advise my patients to increase their chocolate intake based on this research, particularly if they are overweight.”