By David L. Katz, MD, Yale University

Colleagues and I just published a paper in the American Journal of Clinical Nutrition demonstrating beneficial effects of both solid dark chocolate and liquid cocoa on blood pressure, and blood flow, in overweight adults.  This adds to an impressive body of work suggesting potential health benefits of dark chocolate.  But even data dipped in chocolate require some interpretation.

A short term benefit of dark chocolate on various measures of cardiovascular risk is now well established.  The ingestion of dark chocolate, generally defined as a product with a cacao (often, but incorrectly, referred to as cocoa) content of 60% or more tends to reduce the stickiness of platelets, an aspirin-like effect.  Studies suggest anti-inflammatory effects, antioxidant effects, reductions in both cholesterol and insulin levels, and as in our study, reductions in blood pressure and enhanced blood flow as well.

The novelties in our study include the testing of both solid dark chocolate and liquid cocoa in the same subjects, as well as the comparison of standard and sugar-free cocoa.  As compared to cocoa-free placebos, each of the preparations containing cocoa reduced blood pressure significantly 2 hours after ingestion, by roughly 3 points.  In a paper soon to be published, we report that similar benefits were seen from drinking cocoa daily for 6 weeks, without weight gain resulting.

The primary outcome in our study is called endothelial function.  The endothelium is the inner lining of blood vessels, and the cells there release chemicals that tell blood vessels when to constrict and when to dilate.  We use an ultrasound machine to measure the change in diameter of a blood vessel in the arm, called the brachial artery (if you can find a pulse in the front of your elbow, that’s it), because its behavior is a reliable predictor of the behavior of the coronary blood vessels that supply the heart.

We observed significant enhancement of endothelial function with roughly 2.5 ounces of dark chocolate, or a single cup of cocoa.  Again, similar benefits were seen with daily cocoa ingestion.  The enhancement of endothelial function, and the reduction in blood pressure, were greater with sugar-free cocoa than with regular, suggesting that sugar may compete with some of the beneficial effects of cocoa.

Such benefits of dark chocolate make good sense.  Cocoa is actually the most concentrated source of antioxidant nutrients, called flavonoids, commonly available to us.  Heart health benefits from dark chocolate may also relate to its high content of magnesium and fiber.

The most interesting thing about dark chocolate is that it is clearly heart healthy despite being rich in saturated fat.   But not all saturated fat is created equal.  The particular variety of saturated fat that predominates in dark chocolate, called stearic acid, does not raise cholesterol or harm blood vessels.  This is in contrast to the varieties of saturated fat that predominate in dairy and most meats, palmitic and myristic acid, which do.  Milk chocolate is both lower in antioxidant content, and higher in potentially harmful fat content, than dark chocolate, and does not offer cardiovascular benefit.

As a personal fan of dark chocolate, I suspect another benefit as well.  If you compare a dark chocolate bar to a milk chocolate bar, you will find the former has fewer ingredients, meaning there is less to compete with the native taste of chocolate.  That, combined with the slight bitterness when cocoa content is high, means it takes less to feel satisfied.  Whereas sweet tends to put the appetite center into overdrive, a bit of bitterness tends to help shut it down.  I love dark chocolate, but there is only so much I can eat.  And since too much of even a good thing is not a good thing, the fact that dark chocolate seems to help regulate its own dose is, well, a good thing.

Along with the CDC, which supports my lab, our study was sponsored by Hershey, which of course makes and sells chocolate.  Corporate sponsorship always, and rightly, raises concerns about bias in research; studies have shown that company-sponsored studies tend to favor the interests of the sponsor.  Certainly our results are everything Hershey could have hoped for.  But we carefully build into our study methods protection against bias, such as analyzing the data before we break the code to see which subjects were getting active treatment and which, placebo.  Defense against bias may never be perfect, but ours is pretty darn good.

While we know with ever greater confidence that cocoa offers heart health benefits, we don’t yet know for sure how to apply that information.  Should people eat or drink cocoa daily, every other day, or weekly?  If so, how much?  If chocolate is added to the diet, is there a risk of weight gain that might offset other benefits?  More research, perhaps some of it our own, will answer these questions eventually.

For now, here’s my advice.  If milk chocolate is part of your diet, switch out for dark chocolate.  Your taste buds will adjust, and likely come to prefer the dark side if you give them a chance.  Make this switch, and you’ll turn a food you love into a food that loves you back.

As for adding chocolate to your diet, the case to me seems very much like that for red wine, which also has known cardiac benefits: some is good, more is not necessarily better.  If you can make room in your diet for 1 to 3 oz of dark chocolate, or a cup of cocoa daily without gaining weight, it will likely be good for your heart.  For what it’s worth, my wife and I often find a bit of dark chocolate can help brighten our darker moods into the bargain.

Originally published as
Preventive Medicine Column, NYTimes Syndicate, July 12, 2008

David L. Katz, MD, MPH, FACPM, FACP

Director, Yale-Griffin Preventive Research Center, Yale University School of Medicine

Medical Contributor, ABC News

www.davidkatzmd.com