Researchers found that adults in the study who ate chocolate at least once a month — or more frequently than that — had rates of atrial fibrillation that were 10 to 20 percent lower than those who ate chocolate less than once a month, according to the findings published today (May 23) in the journal Heart.
Atrial fibrillation is a condition in which the heart's two upper chambers, known as the atria, do not beat at the same pace as the heart's two lower chambers, resulting in an irregular heartbeat. The condition increases a person's risk of strokes, heart failure and cognitive impairment.
The study found that the strongest overall effects were seen in men and women who ate 1 ounce of chocolate, two to six times per week, said the lead author of the study, Elizabeth Mostofsky, a researcher at the Harvard T.H. Chan School of Public Health and at Beth Israel Deaconess Medical Centerin Boston. [5 Surprising Ways to Be Heart Healthy]
One ounce of chocolate is equal to about three or four small, individual Dove Bar squares, for example, Mostofsky said.
Between 2.7 million and 6.1 million Americans have atrial fibrillation, so it's important to identify effective ways to help prevent the condition from developing, the researchers wrote in their study.
Two previous studies have looked at the connection between chocolate consumption and the risk of developing atrial fibrillation, but the results from both of those studies suggested that any association found may be due to chance.
Unlike those two earlier studies, whose participants were only men or only women, the new study included both men and women. And the new study also included adults who had been clinically diagnosed with atrial fibrillation rather than people who had self-reported the condition, as was the case with the previous studies.
In the new study, the researchers analyzed data collected from more than 55,000 adults between ages 50 and 64 in Denmark. All of them were participants in an ongoing study called the Danish Diet, Cancer and Health Study. [5 Wacky Things That Are Good for Your Health]
When the participants were first recruited for the study between 1993 and 1997, they completed a detailed food-frequency questionnaire. One of those questions asked how frequently the participant ate chocolate during the past year.
Chocolate in moderation
The researchers found that more than 3,300 adults were diagnosed with atrial fibrillation or atrial flutter (a condition in which the heart beats faster than usual, but is not irregular) over the follow-up period of 13.5 years, on average.
When researchers took into consideration other factors that could influence people's development of atrial fibrillation, such as alcohol intake, smoking, obesity, high blood pressure and cholesterol levels, the study showed an association between people with a moderate intake of chocolate and a lower risk of developing atrial fibrillation.
The study does not prove there is a cause-and-effect relationship between eating chocolate and a lowered risk of atrial fibrillation. And although the exact mechanism of how chocolate may prevent atrial fibrillation is not known, it's possible that compounds in chocolate called flavonoids may play a role, the researchers said.
Flavonoids have anti-inflammatory and antioxidant properties, Mostofsky said. They may limit the inflammatory process in the body, reducing the stickiness of the blood and leading to less scarring of connective tissue. All of these factors may help prevent the electrical remodeling of the heart that leads to atrial fibrillation, she explained.
The findings showed that for women, the strongest association was seen in those who ate a 1-ounce serving of chocolate, once a week – this level of consumption was linked to a 21 percent lower risk of atrial fibrillation. For men, the strongest association was seen in those who ate two to six 1-ounce servings of chocolate weekly. These men had a 23 percent lower risk of atrial fibrillation.
All in all, the findings suggest that compared with some other snack choices, a moderate intake of chocolate may be a heart-healthy snack, Mostofsky told Live Science. But people should choose chocolate with a higher cocoa content, which has more health benefits and protective compounds, she said.
One of the limitations of the study is that people in Denmark are more similar to each other in race and ethnicity than people in other countries, so the findings may not be generalizable to other populations, other researchers wrote in an editorial accompanying the study.
The chocolate consumers in the study were also generally healthier, better educated and had lower rates of high blood pressure and diabetes than the people who didn't eat chocolate, and all of these factors could lessen their odds for atrial fibrillation, wrote the editorial authors Dr. Jonathan Piccini and Dr. Sean Pokorney. Both doctors are cardiologists at the Duke Center for Atrial Fibrillation at Duke University Medical Center in Durham, North Carolina.
Even so, Piccini and Pokorney said "the findings are interesting and warrant further consideration, given the importance of identifying effective prevention strategies for atrial fibrillation."
Since 25 percent of adults will develop atrial fibrillation over the course of their lifetime, there is a need to identify additional prevention targets, including lifestyle factors, to lower the risk, according to the editorial.