Life history trade-offs with skeletal health among the indigenous Shuar of Amazonian Ecuador

Photo credit: Felicia C. Madimenos

Dr. Felicia C. Madimenos (Queens College / CUNY) describes her collaborative research on the trade-offs between reproduction and skeletal health among the indigenous Shuar of Amazonian Ecuador.

Life history biology describes patterns of growth, reproduction, and aging, and explores how natural selection produces variation in timing and allocation of resources, energetic or otherwise, to key life functions/stages. Based on these principles, all adult organisms face the fundamental trade-off between investing energy into reproduction and somatic repair, under which skeletal growth and maintenance may be theoretically subsumed. Among human females, trade-offs between various reproductive stages, particularly pregnancy and lactation, and skeletal health are therefore expected based on life history principles. Results from clinical and epidemiological literature indicate a complex relationship between reproduction and skeletal health although data are inconsistent regarding the extent to which reproductive factors shape bone loss and accretion in both the immediate and long-term. These inconsistencies may be partly due to the limited datasets from non-Western, non-clinical populations. Even fewer data are available for subsistence-based, natural fertility populations. This is a critical oversight given that reproductive patterns and the associated hormonal cycles of women in these populations are distinct from those of women in industrialized nations (Sperling and Beyene, 1997; Whitten, 2008). Given the enormous health and societal costs of poor skeletal health (e.g., osteoporosis) and the severity of the problem, particularly for women, information from non-Western, natural fertility populations are essential for the reevaluation and development of clinical guidelines and public health policies for osteoporosis prevention.

Using a life history perspective, I investigate the relationship between bone mineral density (BMD), a proxy for skeletal health, and reproductive factors among pre- and post-menopausal women from the Indigenous Shuar forager-horticulturalist population of Amazonian Ecuador. This research is a part of a larger, multi-year research project, The Shuar Health and Life History Project, based out of the University of Oregon (co-directed by Lawrence Sugiyama and J. Josh Snodgrass). While many remote Shuar communities maintain “traditional” hunting and foraging lifestyles, those villages located in close proximity to major town centers are undergoing rapid economic change towards increasing market integration. Other collaborators including Melissa Liebert (U of Oregon), Tara Cepon-Robins (U of Colorado State, Colorado Springs), Aaron Blackwell (UCSB), Samuel Urlacher (Harvard), and Theresa Gildner (U of Oregon) are exploring the varied health consequences associated with this transition. I am also collaborating with researchers from the Tsimane Health and Life History Project to examine the complex relationship between reproductive history and BMD in this Bolivian forager-farming group.

Among the Shuar, preliminary results document that age at menarche has a profound and resonating influence on post-menopausal bone health regardless of the transient effects of additional reproductive factors during the individual’s pre-menopausal life (e.g., number of live births, lactation patterns) (Madimenos et al., 2012). This phenomenon emphasizes the criticality of early developmental stages in regulating health outcomes later in life and highlights the necessity of applying a life-course perspective to understand issues related to health and disease.  As a result of these findings, I am currently examining skeletal health in Shuar sub-adults (< 18 years old) and contextualizing early developmental life so as to further shed light onto adult skeletal health. BMD data among subsistence-based groups are not only informative from an anthropological and evolutionary perspective, they also provide a critical step towards improving knowledge of skeletal health in non-urbanized, economically-transitioning contexts, thereby increasing osteoporosis awareness in these regions, where diagnostic resources are essentially non-existent.

References

Madimenos FC, Snodgrass JJ, Liebert MA, Cepon TJ, and Sugiyama LS. 2012. Reproductive effects on skeletal health in Shuar women of Amazonian Ecuador: a life history perspective. Am J Hum Biol 24(6):841-852.

Sperling S, Beyene Y. 1997. A pound f biology and a pinch of culture or a pinch of biology and a pound of culture. In: Hager L (Ed). Women in human evolution. New York: Routledge. Pp. 137-152.

Whitten PL. 2008. Diet, hormones, and health: an evolutionary-ecological perspective. In Panter-Brick C, Worthman C (Eds). Hormones, health, and behavior: a socio-ecological and lifespan perspective. Cambridge: Cambridge University Press. Pp. 210-243.