Estrogen, energy, and bone: a life history approach to understanding skeletal phenotypes

Bone is affected by estrogen throughout the lifespan. Changing concentrations of estrogen shape the structure of bone and influence bone maintenance processes over time. Understanding bone health in women as both a function of earlier life experiences, as well as a reflection of current reproductive status and physical activity patterns, can help identify key factors that explain variation in bone properties and health. Age of menarche (first period), parity (number of offspring), and duration of breastfeeding are life history traits which reflect changing estrogen concentrations. These traits can change if women are in conditions where they have a deficit or surplus of available energy. Because estrogen is an important component of bone development and maintenance in women, these life history traits are likely to affect bone. Bone is a dynamic tissue throughout the lifespan, however, and physical activity and estrogen levels in adulthood are important for maintaining bone density for later in life. I use measurements of bone density and bone turnover to understand the slowly changing state of bone (density) and the physiological processes which maintain that state (bone turnover) in two related populations with different lifestyles. This work compares healthy premenopausal 2nd and 3rd generation Polish-American women in industrialized locales with rural Polish women from a population that is transitioning from subsistence agriculture to a more market-based economy. I extend the life history concept of resource allocation to include bone maintenance as one of the tradeoffs between growth, maintenance, and reproduction. Additionally, I contribute to broader anthropological discussions regarding health effects of demographic transitions to sedentary industrialized lifestyles. The major contributions of my work are 1) integrating life history theory with studies of bone phenotype in a population of living women; 2) measuring the effects of habitual low-intensity activity on bone phenotype and bone maintenance; 3) examining several inter-related measures of energetic condition and their effects on estrogen across the menstrual cycle; and 4) examining how energy and estrogen affect bone maintenance. Chapter 2 focuses on using a life history approach to understand how life history factors associated with reproduction and anthropometric measures of current body size and habitual use affect frame size and bone density. This chapter focused exclusively on the Polish sample and did not include the U.S. sample of Polish-American women. I found that in this sample habitual activity seems more important than life history factors for bone phenotype when measured as frame size and bone density. Chapter 3 tests how physical activity (measured as steps per day and time active at different intensities) affects cortical bone density of the radius and the tibia as well as whether physical activity is associated with bone metabolism processes. The focus on steps and time active is intended to test hypotheses about activity acting as a mechanical stimulus for bone maintenance. This chapter includes data from both the Polish and U.S. samples. I found that the Polish sample spent significantly more time active each day at light intensity than the U.S. sample, which suggests that the types of daily activities are likely very different between the two samples. The Polish sample had very high bone density of the radius but largely my results emphasized how difficult it is to measure habitual physical activity of the upper limb in a free-living population. Finally, in Chapter 4, I use the same samples of Polish and Polish-American women to examine how bone metabolism processes are affected by several different measures of energy expenditure, energy status, and estrogen concentrations. I emphasize how measures of energy are inter-related, and I largely found that energetic reserve (measured using BMI) and energy expenditure (estimated in kcal) are more associated with bone metabolism than other measures of energy. Overall, these results highlight how context shapes bone phenotype and show the importance of further study of diverse women to understand bone maintenance processes in healthy-premenopausal women.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Anthropology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2020

Author dc:creator

• Lee, Katharine Marie Nobes

Contributors dc:contributor

• Clancy, Kathryn BH
• Shackelford, Laura L
• Hughes, Cris E
• De Souza, Mary Jane

• physical activity
• bone turnover
• life history theory
• bone density
• frame size
• skeletal biology
• women's health
• feminist biology

Statement dc:rights

• Copyright 2020 Katharine MN Lee

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/108611

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/108611