Impact of age on the association between body mass index and all-cause mortality in patients with atrial fibrillation

OBJECTIVES: To explore the impact of age on the association between body mass index (BMI) and all-cause mortality in patients with atrial fibrillation (AF). METHODS: A total of 1991 patients with AF (69 ± 13 years, 54.9% female) were divided into three age groups: < 65 years, 65-75 years, and > 75 years, and followed for one year. The primary outcome was defined as all-cause mortality, with secondary outcomes including thromboembolism and major bleeding. Cox regression models were utilized to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). RESULTS: Compared to patients aged < 65 years, elder groups had much lower BMI and more comorbidities other than a lower prevalence of valvular heart disease. During one-year follow-up, 277 (13.9%) patients died, 158 (7.9%) underwent thromboembolism events and 26 (1.3%) had major bleeding. Mortality and thromboembolism risk were both notably higher in patients with advanced age (all P values < 0.001). Using normal weight patients as reference, mortality risk was significantly lower in overweight (HR 0.548; 95% CI 0.404-0.744) and obese patients (HR 0.536; 95% CI 0.325-0.883) for the entire cohort, with reduced death risk mainly observed in overweight patients aged 65-75 years (HR 0.285; 95% CI 0.131-0.621) and aged > 75 years (HR 0.686; 95% CI 0.473-0.993), but not in patients aged < 65 years. Continuous analyses of BMI indicated consistent results. CONCLUSION: High BMI is associated with reduced mortality rate in patients with AF, and this association is affected by age, with the so-called "obesity paradox" confined to those with advanced age rather than young patients.