Bone Functional Adaptation: Life History Constraints and Implications for Aging Research

Abstract

This dissertation examines skeletal adaptation across human life history, emphasizing how reproductive investment and aging influence bone mineral density (BMD), a crucial determinant of bone health and resilience. Specifically, it investigates how parity, habitual mechanical loading, and cellular aging–proxied by leukocyte telomere length (TL)--interact to shape regional variation in BMD. The first study analyzed associations between parity and regional BMD using anthropometric, dual-energy X-ray absorptiometry, health biomarker, and questionnaire data from the National Health and Nutrition Examination Survey (NHANES cohorts 2007–2018). Results showed that higher parity was linked with lower BMD, particularly in metabolically active skeletal sites such as the lumbar spine, highlighting the metabolic demands of reproduction on skeletal maintenance. The second study assessed whether habitual mechanical loading could buffer age-related BMD loss by comparing weight-bearing and non-weight-bearing skeletal regions. Findings demonstrated similar age-related declines between weight-bearing and non-weight-bearing regions, though gendered differences emerged; women experienced steeper declines in non-weight-bearing regions compared to weight-bearing regions, indicating that loading alone is insufficient to protect against aging-related skeletal deterioration. The third study investigated whether telomere length, a biomarker of cellular aging, is associated with regional BMD variation and parity (NHANES 1999–2002). Results showed that shorter TL correlated with lower BMD selectively in women but did not mediate the association between parity and BMD. Together, these findings demonstrate that reproductive history and cellular aging independently influence skeletal health across the lifespan. This dissertation emphasizes the complexity of skeletal aging and the importance of integrating life history theory, biomechanical analysis, and cellular biology to understand bone health in evolutionary, clinical, and public health contexts.