Hormonal and nutritional factors affecting bone mineral density in young women and statistical methods for epidemiology

Young female athletes are at risk for the female athlete triad, a syndrome composed of three interrelated disorders: disordered eating, menstrual irregularity, and low bone mineral density (BMD). The relationships between (a) disordered eating (elevated scores on an eating disorder inventory [EDI]) and menstrual irregularity (oligo/amenorrhea: 0–9 menses during the past year), (b) menstrual irregularity and low BMD, and (c) disordered eating and low BMD were investigated in 91 competitive female distance runners aged 18–26 years, 36% of whom were oligo/amenorrheic. We conclude that, in young competitive female distance runners, (i) disordered eating is strongly related to menstrual irregularity, (ii) menstrual irregularity is associated with low BMD, and (iii) disordered eating is associated with low BMD in the absence of menstrual irregularity.; To examine whether exposure to oral contraceptives (OCs) is associated with bone mineral density (BMD) in young women, we studied, cross-sectionally and longitudinally, 216 white and 260 black women enrolled in the Coronary Artery Risk Development in Young Adults (CARDIA) study. After adjustment for other relevant variables, we found that cumulative estrogen from OCs (mg) explained 4.0% of the variation in spine BMD (p = .024) among white women, but did not explain any of the variance in BMD in black women. Cumulative OC estrogen was associated with a decreased risk for low bone density (lowest quartile) at the spine, hip, and whole body in white women. OC exposure was not related to low bone density in black women. These results suggest that exposure to the estrogen from OCs during the premenopausal years may have a small beneficial effect on the skeleton in white women. Benefit is proportional to the cumulative estrogen exposure, suggesting that previous cross-sectional studies that considered OC use as a dichotomous variable may have lacked the power to detect an association.; The third chapter of this thesis deals with the future of epidemiology. Although not specifically relevant to osteoporosis, the statistical method of two-stage sampling, described in this chapter, has applications for the epidemiologic study of osteoporosis and fractures, particularly in exploring the associations between new drugs and osteoporotic fractures in large populations of women.