(HealthDay News) — Greater physical activity is associated with lower rates of incident atrial fibrillation (AF) in women, according to a study published online August 20 in the Journal of the American Heart Association.

Farnaz Azarbal, MD, from Stanford University in California, and colleagues followed 93,676 postmenopausal women (7.8% African-American and 3.6% Hispanic) participating in the Women’s Health Initiative (WHI) Observational Study for an average of 11.5 years. WHI-ascertained hospitalization records and Medicare claims were used to identify incident AF.

The researchers found that 9,792 of 81,317 women (average age, 63.4 years) developed AF. Women with prevalent AF, incomplete data, or underweight body mass index (BMI) were excluded. After multivariate adjustment, increased BMI (hazard ratio [HR], 1.12 per 5kg/m² increase) and reduced physical activity (>9 vs. 0 metabolic equivalent task hours per week; HR, 0.90) were independently associated with higher rates of AF. The AF risk conferred by obesity was reduced with higher levels of physical activity (interaction P=0.033).

“Greater physical activity is associated with lower rates of incident AF and modifies the association between obesity and incident AF,” the authors write.

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