Predictors of bone density in nulliparous, young women: The role of age of menarche and body composition.

Fractures represent significant personal and economic costs in elderly women. One risk factor for fracture, low bone mineral density, is hypothesized to result from the failure to achieve a high peak density in early adult years. To develop strategies to maximize peak bone density, an increased understanding of the factors influencing bone density during this period is needed. This dissertation describes a cross-sectional study of the correlates of bone density in a population of nulliparous, Caucasian, University of Michigan women, ages 19-26 (n = 182). The objectives of the study were to: (a) describe the relationships of current and historical measurements of menstrual characteristics, body composition, physical activity, diet, and lifestyle with measurements of bone density at the lumbar spine and femoral neck; and to (b) determine if late age of menarche and smaller body size (Quetelet index) could independently or interactively predict low measures of bone density. No significant interactions of age of menarche and body size with bone density at either site were found. Smaller body size was a negative predictor of both lumbar spine and femoral neck bone density. Later age of menarche also predicted lower bone density at the lumbar spine and femoral neck. At the spine the effect was independent of body size, while at the femoral neck the effect was negated after adjusting for Quetelet index. At both sites, adjusting for height or kilograms of lean body mass strengthened the negative association. Variables in multiple regression models explained approximately 20% of the variance at each site. At the lumbar spine, significant predictors of higher bone density were early age of menarche, larger body size, increased height, and high self-reported activity in high school. An additional predictor of high bone density at the femoral neck was current aerobic activity. Future research should further explore the mechanisms by which age of menarche is associated with lower bone density, specifically characterizing the hormonal profiles of women as they progress from menarche to adulthood. Research should also delineate the important components of body composition, as well as the critical levels of activity that influence peak bone density.