ObjectiveWe investigated the association between obesity and biomarkers indicating cardiac or renal dysfunction or inflammation and their interaction with obesity and outcomes.MethodsA total of 14 753 patients in the Apixaban for Reduction In STroke and Other ThromboemboLic Events in Atrial Fibrillation (ARISTOTLE) trial provided plasma samples at randomisation to apixaban or warfarin. Median follow-up was 1.9 years. Body Mass Index (BMI) was measured at baseline and categorised as normal, 18.5–25 kg/m²; overweight, >25 to <30 kg/m²; and obese, ≥30 kg/m². We analysed the biomarkers high-sensitivity C reactive protein (hs-CRP), interleukin 6 (IL-6), growth differentiation factor-15 (GDF-15), troponin T and N-terminal B-type natriuretic peptide (NT-pro-BNP). Outcomes included stroke/systemic embolism (SE), myocardial infarction (MI), composite (stroke/SE, MI, or all-cause mortality), all-cause and cardiac mortality, and major bleeding.ResultsCompared with normal BMI, obese patients had significantly higher levels of hs-CRP and IL-6 and lower levels of GDF-15, troponin T and NT-pro-BNP. In multivariable analyses, higher compared with normal BMI was associated with a lower risk of all-cause mortality (overweight: HR 0.73 (95% CI 0.63 to 0.86); obese: 0.67 (0.56 to 0.80), p<0.0001), cardiac death (overweight: HR 0.74 (95% CI 0.60 to 0.93); obese: 0.71 (0.56 to 0.92), p=0.01) and composite endpoint (overweight: 0.80 (0.70 to 0.92); obese: 0.72 (0.62 to 0.84), p<0.0001).ConclusionsRegardless of biomarkers indicating inflammation or cardiac or renal dysfunction, obesity was independently associated with an improved survival in anticoagulated patients with AF.Trial registration numberNCT00412984.