Researcher Dr. Murray Mittleman, director of the Cardiovascular Epidemiology Research Unit at Harvard Medical School's Beth Israel Deaconess Medical Center in Boston, led the 9-year study, conducted among 31,823 middle-aged and elderly Swedish women.
The study found women who ate an average of one to two servings of high-quality chocolate per week had a 32 percent lower risk of developing heart failure and those who ate one to three servings per month had a 26 percent lower risk but those who ate at least one serving a day or more didn't appear to benefit.
That those eating the chocolate daily may have no protective effect is probably due to the additional calories gained from eating chocolate instead of more nutritious foods, Mittleman says.
Although 90 percent of all chocolate eaten in Sweden was milk chocolate, it contained about 30 percent cocoa solids, while U.S. standards require only 15 percent cocoa solids to qualify as dark chocolate. As a result, American chocolate may have fewer heart benefits and more calories and fat for equivalent amounts in Sweden.
The average serving size for Swedish women was 19 grams among those age 62 and older, compared to 30 grams among those age 61 and younger, but the standard American portion size is 20 grams.