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Objectives To investigate the association between mortality and heritability of a rescaled Fried frailty index, the Scale of Aging Vigor in Epidemiology ( SAVE), to determine its value for genetic analyses. Design Longitudinal, community-based cohort study. Setting The Long Life Family Study ( LLFS) in the United States and Denmark. Participants Long-lived individuals (N = 4,875, including 4,075 genetically related individuals) and their families (N = 551). Measurements The SAVE was administered to 3,599 participants and included weight change, weakness (grip strength), fatigue (questionnaire), physical activity (days walked in prior 2 weeks), and slowness (gait speed); each component was scored 0, 1, or 2 using approximate tertiles, and summed (range 0 (vigorous) to 10 (frail)). Heritability was determined using a variance component-based family analysis using a polygenic model. Association with mortality in the proband generation (N = 1,421) was calculated using Cox proportional hazards mixed-effect models. Results Heritability of the SAVE was 0.23 ( P < .001) overall (n = 3,599), 0.31 ( P < .001) in probands (n = 1,479), and 0.26 ( P < .001) in offspring (n = 2,120). In adjusted models, higher SAVE scores were associated with higher mortality (score 5-6: hazard ratio ( HR) = 2.83, 95% confidence interval ( CI) = 1.46-5.51; score 7-10: HR = 3.40, 95% CI = 1.72-6.71) than lower scores (0-2). Conclusion The SAVE was associated with mortality and was moderately heritable in the LLFS, suggesting a genetic component to age-related vigor and frailty and supporting its use for further genetic analyses. [ABSTRACT FROM AUTHOR]