Determinants of peak bone mass in young premenopausal women
Peak bone mass is defined as the highest level of bone mass attained during life through normal growth, and small increases in peak bone mass may prevent osteoporotic fractures later in life. Non-modifiable genetic factors account for as much as 50-70% of the variation in peak bone mass, but to achieve full genetic potential an individual must work to optimize the modifiable environmental and lifestyle factors that also contribute to the variation in peak bone mass. Thus, understanding these modifiable factors affecting peak bone mass is important for osteoporosis prevention.
The first paper of this dissertation examines the association between peak bone mass and body composition. Previous studies of this association are based on size-dependent bone mass measures, so the true association between body composition and peak bone mass has remained unclear. In size-adjusted analyses, we found that lean mass was positively associated peak bone mass, while fat mass measures were inversely associated with peak bone mass. This analysis clarifies that lean mass, and not fat mass, is important to peak bone mass in young premenopausal women. Women in this group should maintain a healthy body fat percentage to ensure attainment and maintenance of optimum peak bone mass.
The second paper of this dissertation examines the association between overall diet quality and peak bone mass using established indices of diet quality. We found no association between these established diet quality scores and bone mass, suggesting these scores may not be appropriate for use in studies related to bone. Because scores measuring overall diet are important for epidemiologic research, a score specifically tailored to reflect bone-specific dietary components would benefit future research.
The third paper of this dissertation evaluates the relative contribution of bone-related clinical and lifestyle factors to peak bone mass. We found that waist circumference explained the most variation in peak bone mass, and that physical activity measures, dietary factors, and age at menarche were also important. These findings inform osteoporosis prevention, and factors identified in this analysis are appropriate for use in a clinical setting as part of a prescreening tool for low peak bone mass.