Obesity is a risk factor for atrial fibrillation among fertile young women: a nationwide cohort study

Obesity has been associated with increased risk of atrial fibrillation (AF), but whether this risk is also prevalent in younger individuals is unknown. We therefore investigated the risk of AF in relation to body mass index (BMI) among young fertile women. By cross-linkage of nationwide registers of childbirth and hospitalization, we identified 271 203 women without prior AF who gave birth in Denmark between 2004 and 2009. Body mass index (kg/m(2)) was examined as a risk factor for AF using proportional hazard models. Mean age was 30.6 years (4.7 SD) and median follow-up was 4.6 years (interquartile range 2.95.8). During the follow-up, 110 women were hospitalized with first-time AF; very few individuals had known risk factors for AF. Overall incidence rate of AF was 9.3 [95 confidence interval (CI): 7.711.2] per 100 000 person-years. According to BMI, the incidence rate of AF per 100 000 person-years was 7.4 (5.69.7) in normal weight (BMI: 18.524.9), 8.5 (5.513.1) in overweight (BMI: 2529.9), 15.8 (9.326.7) in obese (BMI: 3035), and 27.3 (15.548.1) in very obese (BMI 35) individuals. Multivariable regression analyses adjusted for age, hyperthyroidism, and previous use of beta-blockers revealed a hazard ratio of 2.04 (95 CI: 1.133.69) in the obese and 3.50 (1.866.58) in the very obese individuals compared with normal weight. Obesity is a risk factor for AF among young and essentially healthy fertile women despite the low incidence of AF. These results may have implications for prevention of AF.