Obesity, Physical Activity, and Their Interaction in Incident Atrial Fibrillation in Postmenopausal Women

Abstract

Background Atrial fibrillation ( AF ) is the most common cardiac arrhythmia and is associated with increased risk of stroke and death. Obesity is an independent risk factor for AF , but modifiers of this risk are not well known. We studied the roles of obesity, physical activity, and their interaction in conferring risk of incident AF . Methods and Results The Women's Health Initiative ( WHI ) Observational Study was a prospective observational study of 93 676 postmenopausal women followed for an average of 11.5 years. Incident AF was identified using WHI ‐ascertained hospitalization records and diagnostic codes from Medicare claims. A multivariate Cox's hazard regression model adjusted for demographic and clinical risk factors was used to evaluate the interaction between obesity and physical activity and its association with incident AF . After exclusion of women with prevalent AF , incomplete data, or underweight body mass index ( BMI ), 9792 of the remaining 81 317 women developed AF . Women were, on average, 63.4 years old, 7.8% were African American, and 3.6% were Hispanic. Increased BMI (hazard ratio [ HR ], 1.12 per 5‐kg/m 2 increase; 95% confidence interval [ CI ], 1.10 to 1.14) and reduced physical activity (>9 vs. 0 metabolic equivalent task hours per week; HR , 0.90; 95% CI , 0.85 to 0.96) were independently associated with higher rates of AF after multivariate adjustment. Higher levels of physical activity reduced the AF risk conferred by obesity (interaction P =0.033). Conclusions Greater physical activity is associated with lower rates of incident AF and modifies the association between obesity and incident AF .