So that’s what chocolate is for!
Q: Have you seen the new story in Stuff about chocolate being good for your heart?
A: Indeed. A fine example of the genre.
Q: What did the researchers find out about the benefits of chocolate this time?
A: Absolutely nothing. (Here’s the research paper)
Q: Then what is the story about?
A: They assumed that there were significant cardiovascular benefits of high-cacao dark chocolate, based on short-term studies of blood pressure and cholesterol, and worked out what the population impact of chocolate therapy would be if that was true.
Q: And is it true?
A: That’s not clear. If you remember the last time we encountered ‘chocolate for health’, the benefits in that study were pretty marginal. This time the researchers cite a pooled set of studies giving a somewhat larger estimate of the benefits. Also, the research showing benefits on blood pressure and cholesterol has been from very short-term studies, and extrapolating to the longer-term may well be unreliable. Still, as Prof Reid points out, no-one is going to do any reliable studies, so extrapolation is what we’ve got.
Q: What about the calories and fat?
A: Well, the studies that provided the estimates of benefit compared chocolate or cocoa powder to a control that supplied the same calories and fat, so we don’t know. The researchers (and even the newspaper) admit “The study did not take into account weight gain … ”but that is something you would need to consider,” [Prof Chris Reid] said.”
Q: Ok, if we stipulate all of that, how big were the benefits?
A: Moderate: treating 10,000 high-risk people with chocolate would, under the most favorable assumptions, prevent about 15 fatal and 70 non-fatal heart attacks and strokes over a ten-year period.
Q: How do the benefits compare to pills?
A: Well, thiazide diuretics provide 2-3 times the blood pressure effect, and simvastatin provides maybe 10 times the cholesterol reduction. And they cost Pharmac less per month than the chocolate would cost you per day. And we really know the reductions in risk factors translate to fewer heart attacks, strokes, and deaths
Q: But didn’t the researchers say that chocolate therapy would be cost-effective?
A: They said it would be cost-effective at a cost of $42/year. According to their website, if you wander down to your local Countdown, you can currently get Whitaker’s Dark Ghana at $3.79 for 250g. That would be $550/year for the 100g/day dose in the paper. And that’s a sale price. It’s only cost-effective if you don’t count the cost of the chocolate.
Q: How about cocoa powder?
A: One of the studies that went into the analysis used 31g/day of cocoa powder (`natural’ not Dutch process). That’s cheaper, but it’s still a lot more than $42/year, and 5 tablespoons/day is a lot of unsweetened cocoa powder.
Q: So, should I eat dark chocolate?
A: If you like it, sure. If you’re just choking it down for the cardiovascular benefits, probably not.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »