Harvard Heart Letter

Taking the myth (and, alas, some of the romance) out of chocolate and the heart

The approach of Valentine's Day each year brings the latest crop of "chocolate is good for your heart" articles. We would all like to believe that a sweet treat protects the heart and arteries. But that notion isn't completely supported by the evidence.

Some studies show a strong connection between eating chocolate and less heart disease. In a survey of nearly 5,000 American adults, those who said they ate chocolate five times a week were 40% less likely to have ever had a heart attack or to have needed an artery-opening procedure (Clinical Nutrition, December 2010). A similar trend was seen in a large German study. In these types of studies, though, it is impossible to tell if eating chocolate protects the heart and arteries or if people who eat chocolate also do other things that are responsible for this protection.

What about clinical trials, which tend to yield better evidence? A number of trials have tested whether dark chocolate (50% to 70% cocoa) lowers blood pressure more than a cocoa-free placebo. A newly published analysis combined the results of 15 such trials. It showed that daily doses of dark chocolate lowered systolic blood pressure (the top number of a blood pressure reading) by 5 points and diastolic pressure (the bottom number) by 3 points — but only among people with high blood pressure. Chocolate had no effect among people with normal blood pressure (BMC Medicine, published online June 28, 2010).

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