|Van Loan, Marta|
Submitted to: Bone
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2012
Publication Date: 8/27/2012
Citation: Osborne, D.L., Weaver, C.M., Mccabe, L.D., Novotny, R., Mccabe, G.P., Van Loan, M.D., Going, S., Matkovic, V., Boushey, C.J., Savaiano, D.A. 2012. Body size and pubertal development explain ethnic differences in structural geometry at the femur in Asian, Hispanic and white early adolescent girls living in the US. Bone. 10.1016. Interpretive Summary: Osteoporosis is a disease that weakens bone and affects 50% of women over the age of 50 years. Research has also shown differences in the prevalence of osteoporosis in different ethnic groups. Although the disease manifests itself primarily in older women its origin is believed to be during pubertal development when bone growth is at its maximum. Therefore, we evaluated differences in bone structural geometry in 479 Asian, Hispanic, and white adolescent girls aged 9-14 years to determine the influence of ethnicity on indices of skeletal integrity. Bone structure was evaluated using standard bone density measurements with advance analysis of the hip region. The specific region of the hip we evaluated was the narrow neck of the femur, the site for osteoporosis hip fractures. We measured the cross-sectional area of this region. Bone strength improves with a larger cross sectional area because the weight or load placed upon the bone is spread out over a greater area. Thus cross sectional area is an important component to overall bone strength. Body fat and lean masses were measured, dietary intake of calcium was determined and amount of physical activity was assessed. All factors were included in a mathematical model to determine which ones were the most important factors in bone geometry. We found that the most important factors related to the cross sectional area of the neck of the femur were age, time since starting menses, lean mass, fat mass, height, and total calcium intake. However, of all these factors the single most important factor was lean mass, e.g. muscle mass, of the girls. We also found that when lean mass and pubertal status i.e. the start of menses, are consider there were no difference in femoral neck cross sectional area among the ethnic groups. In conclusion, when physiological factors are evaluated relative to bone geometry or strength there are no differences in adolescent girls of different racial groups.
Technical Abstract: Variation in structural geometry is present in adulthood, but when this variation arises and what influences this variation prior to adulthood remains poorly understood. Ethnicity is commonly the focus of research of skeletal integrity and appears to explain some of the variation in quantification of bone tissue. However, why ethnicity explains variation in skeletal integrity is unclear. Methods: Here we examine predictors of bone cross sectional area (CSA) and section modulus (Z), measured using dual-energy X-ray absorptiometry (DXA) and the Advanced Hip Analysis (AHA) program at the narrow neck of the femur in adolescent (9–14 years) girls (n=479) living in the United States who were classified as Asian, Hispanic, or white if the subject was 75% of a given group based on parental reported ethnicity. Protocols for measuring height and weight follow standardized procedures. Total body lean mass (LM) and total body fat mass (FM) were quantified in kilograms using DXA. Total dietary and total dairy calcium intakes from the previous month were estimated by the use of an electronic semi-quantitative food frequency questionnaire (eFFQ). Physical activity was estimated for the previous year by a validated self-administered modifiable activity questionnaire for Adolescents with energy expenditure calculated from the metabolic equivalent (MET) values from the Compendium of Physical Activities. Multiple regression models were developed to predict CSA and Z. Results: Age, time from menarche, total body lean mass (LM), total body fat mass (FM), height, total calcium, and total dairy calcium all shared a significant (pb0.05), positive relationship with CSA. Age, time from menarche, LM, FM, and height shared significant (p<0.05), positive relationships with Z. For both CSA and Z, LM was the most important covariate. Physical activity was not a significant predictor of geometry at the femoral neck (p=0.339), even after removing LM as a covariate. After adjusting for covariates, ethnicity was not a significant predictor in regression models for CSA and Z.