Abstract Body (Do not enter title and authors here): Background: Age has been shown to modify the population-level association between body mass index (BMI) and mortality. However, whether age modifies the association between adiposity-related anthropometrics and adverse outcomes in heart failure (HF) populations has not been systematically explored.

Methods: In this participant-level pooled analysis of five international, multicenter, randomized-controlled trials enrolling adults with HF and either mildly reduced or preserved ejection fraction (HFmrEF/HFpEF), the association between age and adiposity-related anthropometrics (BMI, waist circumference [WC], and waist-to-height ratio [WHtR]) and the primary composite outcome of time-to-first HF hospitalization or cardiovascular (CV) death was evaluated using multivariable adjusted Cox proportional hazards models (stratified by treatment and trial) and restricted cubic splines.

Results: Among 21,606 participants in the analysis (mean age, 71±9 years; 49% female; 83% White; mean BMI, 30±6 kg/m²), 5,350 (25%) were aged <65 years, 8,273 (38%) were aged 65-74 years, and 7,983 (37%) were aged ≥75 years at baseline. Older individuals were more likely to be female, have lower BMI and WC, and higher left ventricular ejection fraction. Overall, BMI, WC, and WHtR were steeply and non-linearly associated with the primary outcome (Figure). Age, as either a categorical or continuous variable, significantly modified the covariate-adjusted association between all anthropometrics and the primary composite outcome (P≤0.001 for all) (Figure). A J-shaped relationship, characterized by higher incidence of the primary outcome with lower anthropometric values, was observed only for BMI and was substantially attenuated among younger adults. Irrespective of the anthropometric used, increasing adiposity was most steeply associated with primary events among adults aged <65 years.

Conclusions: In this pooled analysis of HFmrEF/HFpEF trials, age was a powerful modifier of the relationship between excess adiposity and HF hospitalization or CV death. An “obesity-survival paradox” – observed only for BMI – was not apparent in younger participants, who exhibited the steepest increase in the rate of clinical events with higher adiposity.