Consuming moderate amounts of chocolate was associated with significantly lower risk of being diagnosed with atrial fibrillation — a common and dangerous type of irregular heartbeat — in a large study of men and women in Denmark led by researchers at the Harvard T.H. Chan School of Public Health and in Denmark.

The research was published last month in the journal Heart.

“Our study adds to the accumulating evidence on the health benefits of moderate chocolate intake and highlights the importance of behavioral factors for potentially lowering the risk of arrhythmias,” said lead author Elizabeth Mostofsky, an instructor in the Department of Epidemiology at the Chan School and a postdoctoral fellow at Beth Israel Deaconess Medical Center.

Previous studies have suggested that cocoa and cocoa-containing foods — in particular dark chocolate, which has a higher cocoa content than milk chocolate — confer cardiovascular benefits, perhaps because of their high content of flavanols, which may promote healthy blood vessel function. But there has been only limited research on the association between consuming chocolate and the occurrence of atrial fibrillation, which affects millions of people around the world and is linked with higher risk of stroke, heart failure, cognitive decline, dementia, and death.

The study included 55,502 men and women participating in the Danish Diet, Cancer, and Health Study. Researchers considered body mass index, blood pressure, and cholesterol, which were measured at the time participants were recruited, between December 1993 and May 1997. They also looked at participants’ health conditions, including high blood pressure, diabetes, or cardiovascular disease, and data on their diets and lifestyles, from questionnaires.

Diagnoses of atrial fibrillation were identified from the Danish National Patient Register. There were 3,346 cases among the study participants over a 13.5-year follow-up period. Compared with those who ate a one-ounce serving of chocolate less than once per month, men and women who ate one to three servings per month had a 10 percent lower rate of atrial fibrillation; those who ate one serving per week had a 17 percent lower rate; and those who ate two to six servings per week had a 20 percent lower rate. The benefit leveled off slightly with greater amounts of chocolate consumption, with those eating one or more servings per day having a 16 percent lower rate. Results were similar for men and women.

“Despite the fact that most of the chocolate consumed by the study participants likely had relatively low concentrations of potentially protective ingredients, we still observed a significant association between eating chocolate and a lower risk of atrial fibrillation — suggesting that even small amounts of cocoa consumption can have a positive health impact,” Mostofsky said. “Eating excessive amounts of chocolate is not recommended because many chocolate products are high in calories from sugar and fat and could lead to weight gain and other metabolic problems. But moderate intake of chocolate with high cocoa content may be a healthy choice.”

The senior author of the study was Kim Overdad of Aalborg University Hospital in Denmark. Murray Mittleman, professor of epidemiology at the Chan School, was a co-author. Read more on the research here.

Funding for the study came from grants from the National Heart, Lung, and Blood Institute (HL-115623), the European Research Council (ERC), EU 7th Research Framework Program (281760), a KL2/Catalyst Medical Research Investigator Training award (an appointed KL2 award) from Harvard Catalyst | The Harvard Clinical and Translational Science Center (National Center for Research Resources and the National Center for Advancing Translational Sciences, National Institutes of Health Award KL2 TR001100) and the Danish Cancer Society and the Danish Council for Strategic Research (Aalborg AF-Study Group).