Racial difference in lean mass distribution among reproductive-aged women

Objective: Lean mass is an important determinant of bone mineral density (BMD) accrual, yet data regarding its correlates based on multiethnic premenopausal women are lacking. We examined the influence of age, race/ethnicity, and lifestyle variables on total and regional lean mass distribution in this population. Design: A cross-sectional study was conducted on 708 healthy Black, White, and Hispanic women aged 16-33 years who were seen in an outpatient clinic. In addition, 218 of these women were followed for up to 36 months to observe changes in the relevant variables. We measured body weight, height, and lean mass distribution using a digital scale, wall-mounted stadiometer, and dual-energy absorptiometry (DXA), respectively. Multiple linear regression and mixed-model regression analyses were used to model the relationship of age, race/ethnicity and lifestyle variables to total and regional lean mass. Results: For a given body mass index (BMI), Black women had higher total body lean mass (LM_total) and leg lean mass (LM _leg) than White and Hispanic women. Hispanic women had significantly lower LM_total, trunk lean mass (LM_trunk), and LM _leg than Black and White women. The difference between Blacks and Whites with regard to LM_total significantly magnified with increasing BMI. Weight-bearing exercise and age at menarche were positively associated with lean mass variables, while parity was negatively associated with LM _leg. LM_total and LM_trunk increased over 36 months. Calcium intake was positively associated with increase in LM _total over time. Conclusions: Our study shows that racial differences exist in the distribution of lean mass for a given BMI among reproductive-aged women.