Evaluating the Promise of Biological Aging as a Leading Indicator of Population Health

Abstract

Several substantive observations formed the basis for this research. First, the observation of stagnating life expectancy in the United States over the first two decades of the 21st century, representing a dubious form of American exceptionalism. Second, evidence suggesting that novel measures of biological aging might provide allow for early evaluation of population-level health trajectories, based on direct observation of health status in still-living people. Third, the opportunity to apply these measures for study of population-level phenomena, using methods routinely used in the fields of sociology, demography, and economics. This dissertation represents a proof-of-concept work to support the application of biological aging measures to population health surveillance. In Chapter 2, I conduct a systematic literature review of novel measures and approaches to the quantification of population aging published since 2000, and identify 3 major classes of novel population aging measures. Biological-aging measures can be understood as a specific application of Sanderson and Scherbov’s α-ages approach, which indexes “true age” to the distribution of some aging-related characteristic in a reference sample. Relative to other novel measures and approaches, however, biological-aging algorithms hold particular promise in their ability to provide direct measures of pre-clinical, aging-related health risk across the entire adult age range of a population. In chapters 3 and 4, I apply published biological aging algorithms to blood-chemistry and organ-test data collected by the National Health and Nutrition Examination Surveys (NHANES) to test whether the U.S. population has grown biologically older over the past two decades, as some interpretations of life expectancy data would suggest, and to evaluate the extent to which selected social and environmental exposures might explain these trends. Formal age-period-cohort analysis revealed consistent period increases in biological aging from 1999-2018; while population aging slowed after the training cohort was measured in NHANES III (1988-1994), aging trajectories have reverted towards early-1990s levels since the turn of the century. Limited evidence of cohort effects was observed, with findings consistent regardless of age, race, and sex – although racial disparities in biological aging persisted over the entire study period. Kitagawa-Blinder-Oaxaca decomposition analysis of four candidate exposures (i.e., BMI, smoking status, blood lead, and urinary polycyclic aromatic hydrocarbon levels) suggested that changes in the distribution of behavioral and environmental risk factors accounted for a substantial proportion of observed period trends and/or racial disparities in biological aging over the first two decades of the 21st century. Broadly, these results suggest that measures of biological aging can provide earlier and more precise readouts of population health trajectories and their drivers, ultimately informing next-generation public health efforts to promote healthy aging and aging health equity