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.

Keywords: atrial fibrillation; electrophysiology; epidemiology; exercise; obesity.

Figure 1.

Hazard ratios of incident atrial fibrillation by subgroup of body mass index (obese vs. overweight plus normal weight participants). Hazard ratios are multivariate adjusted for all covariates in the primary model. P values for continuous variables (physical activity, age) are done with separate interaction models of obese (yes/no) versus linear trend across level. CHD indicates coronary heart disease; CHF, congestive heart failure; CI, confidence interval; HR, hazard ratio; MET‐h/wk, metabolic equivalent task hours per week.

Figure 2.

Hazard ratios of incident atrial fibrillation by category of body mass index and physical activity. The normal weight, >9 MET‐h/week category is used as the reference group. Hazard ratios are multivariate‐adjusted for all covariates in the primary model. AF indicates atrial fibrillation; BMI, body mass index; MET‐h/wk, metabolic equivalent task hours per week.