1Anthropology, University of New Mexico, 2Anthropology, University of California-Santa Barbara, 3Anthropology, Queens College-CUNY
March 27, 2015 2:30, Grand Ballroom A/B
Evolutionary theories of aging posit that greater reproductive effort causes somatic decline given a fundamental trade-off between investing energy in reproduction and repair. Few studies in high fertility human populations support this hypothesis, and problems of phenotypic correlation can obscure the expected trade-off between reproduction and somatic condition. This cross-sectional study investigates whether greater reproductive effort is associated with reduced calcaneal bone mineral density (BMD) among female Tsimane forager-farmers of lowland Bolivia. We also investigate whether Tsimane BMD values are lower than sex- and age-matched US reference values, despite the fact that Tsimane engage in higher physical activity levels that can increase mechanical loading. To measure calcaneal BMD, quantitative ultrasonography was performed on 132 Tsimane women (mean ± SD age = 36.7 ± 15.7, range = 15 – 75) that were recruited regardless of their past or current reproductive status. Anthropometric and demographic data were collected during routine medical exams. As predicted, higher parity, short inter-birth interval (IBI), and early age at first birth are associated with reduced BMD among Tsimane women after adjusting for potential confounders. Population-level differences are apparent prior to the onset of reproduction, and age-related decline in BMD is greater among Tsimane compared to American women. Greater cumulative reproductive burden may lower calcaneal BMD individually and jointly with other lifestyle, developmental, and heritable factors. Fitness impacts of kin transfers in adulthood may determine the value of investments in bone remodeling, and thus affect selection on age-profiles of bone mineral loss.
Funding was provided by NIH/NIA (R01AG024119).