About one in four adults will develop atrial fibrillation (the most common type of irregular heartbeat) in their lifetime. That’s a big deal because atrial fibrillation increases risk of stroke by five-fold. Atrial fibrillation also increases risk of heart failure and impaired cognition (brain function). A recent study in the journal Heart showed moderate chocolate intake was associated with a 10 to 20% decreased risk of being diagnosed with atrial fibrillation. But, is nibbling on chocolate for prevention too good to be true?
“Unfortunately, there’s little convincing evidence to support eating chocolate to reduce risk of atrial fibrillation,” says Alice H. Lichtenstein, DSc, director of Tufts’ HNRCA Cardiovascular Nutrition Laboratory, who was not involved in the research. “In the new study, regular, moderate chocolate eaters were less likely to smoke and had lower rates of hypertension, diabetes and heart disease. Although attempts were made to control for these factors in the analysis, they all trended in the same direction, meaning they could have contributed to lower rates of atrial fibrillation, independent of chocolate intake.”
The Study: Researchers looked at self-reported chocolate intake of 55,502 Danish adults (ages 50 to 64) when they enrolled in the study. That was compared with diagnoses of atrial fibrillation 13 years later. Compared with eating chocolate less than once a month, risk of being diagnosed with atrial fibrillation was:
– 10% lower in people who ate 1 to 3 servings (1-ounce each) of chocolate per month
– 17% lower in people who ate 1 serving of chocolate per week
– 20% lower in people who ate 2 to 6 servings of chocolate per week
For women, the heart benefits associated with chocolate plateaued at 1 serving a week. For men, benefits started to plateau at 6 servings a week. More isn’t better.
“Habitually eating too much chocolate can lead to excessive calorie and sugar intake, which increases other health risks, such as weight gain and type 2 diabetes,” says Elizabeth Mostofsky, ScD, MPH, the lead author of the study at Harvard T.H. Chan School of Public Health in Boston. “And keep in mind, the serving size of chocolate was just 1 ounce in the study.” Depending on the size of the chocolate bar (check the wrapper), that’s generally half a bar or less.
Why Chocolate: Cocoa-containing foods like chocolate bars contain anti-inflammatory phytochemicals called flavanols. “Atrial fibrillation involves an inflammatory process that leads to stickiness of the blood and scarring of the heart tissue, which can damage electrical functioning of the heart,” Mostofsky says. “The flavanols in cocoa may potentially decrease the inflammation and scarring that contribute to atrial fibrillation risk.”
The study didn’t track chocolate type. But in Denmark, people mostly eat milk chocolate, which is required to contain a minimum of 30% cocoa solids (versus 43% for dark chocolate) in the European Union. In contrast, the FDA requires milk chocolate to contain a minimum of 10% cocoa solids, and semisweet or bittersweet chocolate, 35% (but no percent is specified for “dark chocolate,” per se). Higher cocoa content generally means more flavanols.
In Perspective: Two previous observational studies in the US have looked at chocolate intake and atrial fibrillation but didn’t show a significant benefit. As Mostofsky and colleagues noted, it’s possible they found atrial fibrillation benefits associated with chocolate in their study because of higher cocoa content of commonly-eaten chocolate in Denmark.
Even so, the new study was observational, so it couldn’t prove cause and effect. The analysis was adjusted for some factors (such as blood pressure, alcohol intake and smoking) that could impact the results. But, data on other factors that influence atrial fibrillation risk, such as sleep apnea and kidney disease, weren’t available.
“Although the results are tempting to embrace, it is important to realize that topping ice cream with hot fudge, even made from dark chocolate, is unlikely to decrease your atrial fibrillation risk,” Lichtenstein says. “There is no way of getting around the importance of a balanced, healthy dietary pattern.”
To learn more: Heart, August 2017