(HealthDay News) -- Eating a small amount of high-quality dark chocolate one to three times a month may help stave off heart failure in women, a new Harvard study suggests.

But if you ingest too much "good" chocolate, that protective effect goes away, according to the researchers who report their finding in the Aug. 17 issue of Circulation: Heart Failure.

"At least for women, consumption of chocolate seems to be associated with a decreased risk of heart failure, but the protective effect was only seen with relatively small amounts of consumption, less than one serving a day," said senior study author Dr. Murray Mittleman. "With higher levels, the benefit appears to be lost and perhaps even [have] a detrimental effect."

While the redeeming health qualities of chocolate have been extolled before, other studies had not specifically looked at heart failure, Mittleman said.

"Up until now, [researchers] were focused on other outcomes, such as the effects on blood pressure and other things," he explained.

And those studies did find that moderate amounts of chocolate do seem to lower blood pressure.

"The beneficial effects on blood pressure are likely an important part of the mechanisms of what we're observing," said Mittleman, who is director of the Cardiovascular Epidemiology Research Unit at Beth Israel Deaconess Medical Center at Harvard Medical School in Boston.

The study authors studied the chocolate-eating habits of 31,823 Swedish women, aged 48 to 83, reported over a period of nine years.

Women who ate one to three servings of chocolate (20 to 30 grams) a month had a 32 percent reduced risk of heart failure, compared to women who did not eat the sweet regularly. More chocolate than that (one to two servings a week), and the benefit disappeared, while much more than that (three to six servings a week), and the risk actually increased by 23 percent.

"Chocolate is still very calorie-dense, and there's fat and sugar that comes along with it, so moderation is a very important part of the story," Mittleman said.

Chocolate in Sweden is held to different quality standards than in the United States, but there are still characteristics one should look for when choosing chocolate, Mittleman said.

The chocolate measured in this study was mostly high-quality dark chocolate without a lot of added sugar, though it was commercially available, he said.

And the higher the cocoa content, the better. The cocoa content of the chocolate consumed by the women in this study was about 30 percent whereas, in the United States, dark chocolate is only required to contain 15 percent cocoa solids.

And 20 to 30 grams would be about half-to-two-thirds of an average American candy bar, Mittleman said.

The heart benefit of dark chocolate could be the result of any number of factors, including more flavanoids, or antioxidants, that can smooth heart function.

Mittleman said there's no reason that the benefits of chocolate wouldn't extend to men as well, but this still needs to be confirmed.

Linda Van Horn, immediate past chair of the American Heart Association's Nutrition Committee and professor in the Department of Preventive Medicine at Northwestern University's Feinberg School of Medicine in Chicago, said people shouldn't misinterpret the study findings as a carte blanche to satisfy their sweet tooth.

"This is not an 'eat all you want' take-home message, rather it's that eating a little dark chocolate can be healthful, as long as other adverse behaviors do not occur, such as weight gain or excessive intake of non-nutrient dense 'empty' calories," she said in a news release issued by the American Heart Association.

Interestingly, an Australian study released last week found that patients would actually prefer taking a pill than chocolate when it comes to controlling blood pressure.

More information

The American Heart Association has more on heart failure.