Big women -- taller, heavier females with a greater body surface area -- have a nearly threefold greater risk of atrial fibrillation or irregular heartbeat than small women, says a 30-year study involving 1.5 million women.

Atrial fibrillation is the most common heart rhythm disorder, with a 20 per cent lifetime risk. It occurs most often in people over 60 years of age and increases the risk of stroke and heart failure. "We found that bigger women have a greater risk of atrial fibrillation," said study author Annika Rosengren, Professor at the Sahlgrenska Academy, University of Gothenburg, Sweden.

"There was a stepwise elevation in risk with increasing body size. The group with the highest body surface area had nearly three times the risk as those with the lowest body surface area," Rosengren said.

Body surface area (BSA) is influenced by both height and weight.  Women were divided into four groups according to BSA. Compared to women with the lowest BSA, those with the highest BSA were 9 cm taller, 28 kg heavier, and had a higher body mass index (BMI: 21 versus 28 kg/m2). Body surface area was calculated by a standard formula based on weight and height. 

During a maximum follow up of 33.6 years, 7,001 women were hospitalised with atrial fibrillation at an average age of 49 years.  Compared to women in the lowest BSA quartile, those in the second, third, and fourth (highest) quartiles had a 1.16, 1.55 and 2.61 times increased risk of atrial fibrillation, respectively, according to the study presented at EuroPrevent 2017, annual congress of the European Association of Preventive Cardiology (EAPC), being held at Malaga, Spain from April 6-8.

"Atrial fibrillation is the result of obesity-related metabolic changes but there is also a second cause," Rosengren said.  "Big people - not necessarily fat, but big - have a larger atrium, which is where atrial fibrillation comes from. People with a bigger atrium have a higher risk of atrial fibrillation," she explained.

"If you are very tall, I think that it could be a good idea to avoid accumulating excess weight. That would apply to both men and women," Rosengren said.