By Lisa Rapaport

(Reuters Health) – Both men and women who are overweight or obese may be more likely to develop an irregular heart rhythm condition known as atrial fibrillation than their counterparts who maintain a healthy weight, a recent study suggests.

In atrial fibrillation, the upper chambers of the heart, or atria, quiver instead of beating to move blood effectively. While the condition has long been linked to obesity, the current study offers fresh evidence of how gender may impact the risk of atrial fibrillation associated with excess weight.

Extremely obese men, for example, were more than four times more likely to develop atrial fibrillation than men who maintained a healthy weight, the study found. By contrast, extremely obese women had almost twice the risk of developing atrial fibrillation as women at a healthy weight.

“Not only does being overweight/obese change the structure of the heart, making it more susceptible to AF development, but other risk factors for AF are more likely to exist in overweight and obese individuals, such as high blood pressure,” said lead study author Jocasta Ball of the Baker Heart and Diabetes Institute in Melbourne, Australia.

“For patients, recognizing that being overweight or obese increases the risk of future AF development and that even small reductions in BMI can reduce this risk should trigger an attempt at weight loss,” Ball said by email.

Atrial fibrillation is the most common heart rhythm disorder, affecting approximately 2 to 3 percent of the world’s population, researchers note in the Journal of the American Heart Association.

For the current study, researchers examined survey data from 24,799 adults in Norway who were followed for an average of about 16 years to see how their weight impacted their chance of developing atrial fibrillation.

Atrial fibrillation most often develops after age 50. At the start of the study, participants were typically in their mid- to late- 30s. Most of them also started out at a healthy weight based on their body mass index (BMI) – a ratio of weight to height.

During the study period, 811 men and 918 women developed atrial fibrillation.

Even when people weren’t seriously overweight, a higher BMI was still tied with a higher risk for atrial fibrillation. For example, compared to a BMI of 23, which falls within a healthy weight range, men with a BMI of 25, which is slightly overweight, were 14 percent more likely to develop atrial fibrillation.

When men had a BMI of 18, which is underweight, they were 25 percent less likely to develop atrial fibrillation than men with a BMI of 23. Men with a BMI of 20, meanwhile, were 14 percent less likely to develop atrial fibrillation than men with a BMI of 23.

For women, the pattern was similar at lower weights but as with heavier individuals, the association between obesity and atrial fibrillation wasn’t as strong as it was with men.

Women with a BMI of 18 were 18 percent less likely to develop atrial fibrillation than women with a BMI of 23, and women with a BMI of 20 had an 11 percent lower risk.

The study wasn’t a controlled experiment designed to prove whether or how obesity causes atrial fibrillation. Researchers also lacked data on changes over time in medical conditions or medication use that might independently influence the risk of atrial fibrillation.

Still, the study adds to the evidence linking excess weight to a higher risk of atrial fibrillation, said Dr. Gregg Fonarow, a cardiology researcher at the University of California Los Angeles who wasn’t involved in the study.

“While the study finds the relationship was stronger in men, both men and women who were overweight or obese according to their body mass index were at increased risk for atrial fibrillation,” Fonarow said by email.

Losing even a little weight may help lower the risk, said Dr. Prash Sanders, a researcher at the University of Adelaide in Australia who wasn’t involved in the study.

“While even small amounts of weight loss can make a difference, we see an even greater magnitude in reduction of risk if more weight loss is achieved,” Sanders said by email. “Importantly, research has demonstrated that the structural and electrical changes we see in overweight and obese individuals are reversible with weight loss.”

SOURCE: Journal of the American Heart Association, online April 19, 2018.