Exploring the Operationalization of Biological Age and its Relationship to Childhood Adversity and Depression

Biological age is of increasing interest to health scholars across disciplines who seek to understand how environmental, social, or economic forces become embodied and influence health across the life course. However, biological age remains an ambiguous, loosely described construct. Furthermore, while numerous biological age biomarkers have been proposed, no “best measure” has been identified. Congruency between the conceptualization and operationalization of biological age is not just an issue of semantics, but has tangible implications for study design and the interpretation of findings. This dissertation examines the conceptual-operational alignment of biological age, and, subsequently employs the new biological age framework to examine the later life biological consequences of childhood adversity. Data for both aims are drawn from the Detroit Neighborhood Health Study, a representative longitudinal cohort study of adults living in Detroit, MI from 2008-2013. In aim 1, we utilized confirmatory factor analysis to test if biological age is best conceptualized as a unidimensional versus multidimensional phenomenon. In our primary analyses, we examined models with one to three factors. Overall, we observed support for a multidimensional model of biological age; the best fit model was comprised of three latent biological age variables which we interpret as dimensions of “epigenetic age,” “systemic biological age,” and “immune age.” Secondary models with additional measures supported a four-factor model, suggesting the separation of the adaptive and innate immune systems into unique aging components. In aim 2, we examined if biological age mediates the relationship of childhood adversity and depression using the biological age dimensions derived in aim 1. We used structural equation modeling with latent variables to estimate total, direct, and indirect effects, examining childhood adversity both by type and cumulatively. In line with prior literature, we observed that childhood adversity is associated with a graded increase in depression. However, we found few direct effects of childhood adversity on measures of systemic, epigenetic, or immune biological age or biological age on depression, and no evidence of mediation. These findings contribute to the growing understanding of biological age and the complex relationship between childhood adversity, biological age, and depression, highlighting the need for further research.