Chocolate Cures? The Research Just Isn’t There

Apr 23, 2015 at 4:04 PM ET

Chocolate can’t cure cancer. It won’t reduce your risk of heart disease, stroke or diabetes. And it certainly doesn’t make you thinner, or boost your vision, or protect your skin. Yet, scientific studies—and pseudoscientific advice—abound when it comes to our favorite candy bars; a PubMed search reveals 3,467 studies that delve into chocolate’s relationship with cancer.

It does sounds like a lot of evidence, so why don’t we believe it?

Well, there’s this brand-new chocolate study in PLoS (full of rigorous, prospective, peer-reviewed research) that found no association between health-related quality of life and chocolate consumption in a sample of 4,600 individuals over the course of two years. Boom.

And it’s not like any of the prior studies that had cast Hershey as a wellness panacea were terribly compelling to begin with—mostly because the research on chocolate and health either involves cells in a petri dish, or rats fed cocoa pellets in controlled laboratory environments. For instance, a 2011 study suggested that a cocoa-rich diet prevented bowel cancer in rats.

So, how do we proceed? First, turn to the comic geniuses at XKCD:

And it’s true. Scientists (heck, even non-scientists) can prove just about anything in a petri dish. When I was in college, I lost a low-paying job as a lab tech because I kept killing off cancer cells by mistake. That’s right. I cured cancer in a petri dish so many times that they fired me. 

I’m not knocking all pre-clinical trials, but note: A study that shows chocolate prevents cancer in rats does not mean that it prevents cancer in humans. It doesn’t even mean that one day, down the line, it might prevent cancer in humans. It means that it prevents cancer in rats—in a laboratory setting. The media clearly misconstrues this.

To be fair, chocolate science isn’t all petri dishes and rodents. We also have a bunch of studies in humans, summarized nicely in this 2011 BMJ literature review. Out of 4,576 studies involving chocolate consumption and heart disease in humans, the researchers found only seven that were robust enough to include in a proper analysis—and not a single randomized, controlled trial among them. (The facts didn’t stop at least one media outlet from reporting that “High Chocolate Consumption May Reduce Heart Disease Risk By One Third.”)

As Dr. Ted Gansler of the American Cancer Society explains, the research just isn’t there yet:

“Clinical trials are considered the strongest kind of evidence for guiding health decisions, but, there is almost no trial evidence directly relevant to chocolate and cancer… There have not been any studies that randomly assign people to consume chocolate or a placebo (sugar pill) and then study the subjects’ risk of developing cancer or, if they already have cancer, its growth and their survival. That type of study produces the strongest evidence and is considered the ‘gold standard’ for research.”

Meanwhile, we do know how harmful large amounts of chocolate can be for health-conscious folk whom, in their attempt to avoid cancer and heart disease, end up binging on candy bars. So, until more research rolls in, Dr. Gansler says, the occasional chocolate bar is fine—but more than that just doesn’t make sense.