Will eating chocolate reduce your risk of atrial fibrillation?

Squares of milk chocolate
26th May 2017

Eating a moderate amount of chocolate has been linked to a reduced risk of atrial fibrillation (AF), new research has suggested, but is the picture really that simple?

AF is one of the most common forms of abnormal heart rhythm and a major cause of stroke. AF often doesn’t cause any noticeable symptoms but can sometimes be felt as an irregular and sometimes fast heartbeat or pulse.

The researchers, from Harvard University, looked at 55,502 participants from the Danish Diet, Cancer and Health Study. They followed them up for an average 13.5 years, during which time there were 3,346 cases of AF. People who previously had AF or cancer, or who hadn’t provided adequate information on their chocolate consumption, were not included in the study.

At the end of the study period, the researchers found that on average, the people who ate chocolate had a lower risk than people who didn’t eat any chocolate. The researchers categorised people according to gender and how much chocolate they ate. 

The researchers found that on average, the people who ate chocolate had a lower risk than people who didn’t

For men, the biggest reduction in risk was seen in people who ate 2-6 servings of chocolate a week – this was linked to a 23 per cent lower risk of AF. For women, the biggest reduction in risk was if they ate one serving of chocolate a week, in which case they had a 21 per cent lower risk of AF. 

It is important to note that this is an association, not cause and effect.

A portion of chocolate was defined as 1 ounce (about 30g). To put this in perspective, a regular bar of Dairy Milk is 45g, and a Wispa bar is 30g. 

Regardless of their chocolate intake, the rate of AF was lower among women than men. But both sexes had a lower risk of AF with higher levels of chocolate intake.

The researchers' theory is that the cocoa in the chocolate and the compounds known as flavanols that can come with this may be responsible for the improvements seen in blood pressure and cholesterol levels, as well as decreasing the risk of some of the negative changes in the heart that can lead to atrial fibrillation. 

They added that “a typical 100 calorie serving of dark chocolate” (this would typically be around 17g or 5 small squares of chocolate) contains 36 mg of magnesium, which has blood-pressure lowering and antiarrhythmic effects. “These properties may explain the lower cardiovascular risk associated with moderate chocolate intake,” they noted in the report.

Most chocolate eaten is Denmark is milk chocolate, so the researchers suggested that their findings may underestimate the protective effects of dark chocolate.

The research adjusted for weight to make sure that differences in weight did not affect the findings. But we do know that obesity is a risk factor for atrial fibrillation, and chocolate is a high-calorie food – so if you put on weight due to eating more chocolate, this won’t help your risk of AF or your health.

The research

Importantly, the researchers only knew participants’ chocolate intake at the start of the study and (for most participants) after five years, which is a huge limitation. The end result is based on figures after an average of 13.5 years of follow up. We don’t know whether the participants’ chocolate consumption changed during that time.

They also do not know whether it was dark or milk chocolate that the participants were eating.

The end result is based on figures after an average of 13.5 years of follow up

The researchers thought that flavanols, which there are more of in dark chocolate that contains more cocoa, were the cause of cardiovascular benefits. 

These results also cannot necessarily be applied to the USA; as chocolate in Europe has a higher cocoa content than chocolate in the United States (minimum 30 per cent for milk chocolate in Europe, compared with minimum 10 per cent in the US).v

The research was based in two specific areas of Denmark – the Aarhus and Copenhagen areas, and all participants were 50-64 years old, and mostly European, which could limit how generalizable these results are to other populations.

A strength of the study is the large number of participants, and that the research took into account participants lifestyle, medical history, and overall calorie intake, so it is less likely that these factors were behind the result that they found. 

The BHF view

Victoria Taylor, Senior Dietitian at the British Heart Foundation, said: “Chocolate, or rather, the cocoa it contains, has previously been linked to a variety of cardiovascular benefits and in this case, people who ate more had a lower risk of developing atrial fibrillation.

“However, although this is a large study, it is only observational and so other factors could also be responsible for the effects seen. The type of chocolate eaten wasn’t recorded either, therefore we can’t directly translate these findings into recommendations. 

“We need additional research to look more carefully at exactly how much cocoa would need to be consumed and how frequently, to see the same benefit.

“If you eat chocolate, keep your portions small and go for dark chocolate with the highest cocoa content,” she recommends.

A reduction in risk of AF isn’t the same as “saving” your heart

Media coverage

The story was widely covered, including in the Daily Mail, Telegraph and the Express

The coverage was mostly accurate but it failed to mention that the chocolate consumption was only measured at the beginning and five years into the study, which is an important limitation to consider.

The Mail headline “Chocolate six days a week will save your heart, chaps... but sorry, ladies, it's only once for you” may have been overstating matters. A reduction in risk of AF isn’t the same as “saving” your heart, as there are many other types heart problems (including coronary heart disease) and eating chocolate will not cure any heart problems that you already have.

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