Predicting active and productive engagement: introducing the index of aging in midlife and beyond (IAM+).

Background and Objectives: Indicators of midlife health decline are needed to determine people's ability to engage in meaningful activities as they age and to implement early interventions to improve long-term health trajectories. Existing measures of physiological aging are unidimensional, expensive, difficult to collect, or focused on advanced disability, making it challenging to identify exposures that contribute to accelerate aging beginning in midlife. Research Design and Methods: Using the Health and Retirement Study (HRS), we developed the Index of Aging in Midlife and Beyond (IAM+), a 10-item scale that accounts for a range of abilities and domains of health using survey items including multimorbidity, functional capacity, and self-reported cognitive, mental, physical, and sensory health. We evaluated overall reliability and variability. Then, we tested the association between physically demanding jobs in ages 51-56 with trajectories of IAM+ scores in midlife and old age. Finally, we considered predictive validity by examining associations between midlife IAM+ scores and later life activity and health outcomes. Results: The IAM+ had acceptable reliability (alpha = 0.739-0.773). Distributions showed substantial variability. Physically demanding jobs were associated with higher IAM+ scores and accelerated increases in scores in midlife; differences in level, but not slopes, were sustained after retirement age. Higher IAM+ scores in midlife predicted reduced engagement in activities 10 years later, including early labor force exits, and predicted allostatic load, frailty, and mortality 20 years later. Discussion and Implications: The IAM+ is an acceptable and accessible new measure for evaluating health in midlife, with many applications for promoting active and productive engagement through later life.