Critical factors for bone health in women across the age span: how important is muscle mass?

OBJECTIVES/
DESIGN: This cross-sectional study of 113 healthy white women, 20-88 years of age, evaluated relationships between bone mineral density (BMD), body composition, calcium (Ca) intake, and physical activity. The analysis was performed in the entire cohort and in groups divided by reproductive/menopausal status (premenopausal, perimenopausal, early postmenopausal, and late postmenopausal).
METHODS: BMD and body composition were measured with Lunar DPX-MD densitometer using specialized software for total body, spine, femur, and forearm. Ca intake from food and supplements was assessed by a food frequency questionnaire. Past physical activity and past and present walking were assessed only in the older cohort using modified version of the Allied Dunbar National Fitness Survey for Older Adults.
RESULTS: The results showed significant reduction of both total body BMD and lean body mass (LBM) of 13% and 12%, respectively, with age. LBM was the strongest determinant of BMD in various skeletal sites in the entire cohort and groups. Ca was positively associated with BMD of various regions of hip in the entire cohort and in the youngest and oldest subjects (r ranging from 0.32-0.56, P <.05, in simple regression), but not in perimenopausal and early postmenopausal women. Past activity (sports and recreation) was positively associated with BMD in total body, spine, hip, and forearm (r ranging from 0.26-0.37, P <.05). Various modes of present walking were positively associated with BMD in regions of femur and forearm.
CONCLUSIONS: These results reveal the importance of lean tissue acting independently on bone at different skeletal sites in women across age groups as well as the positive effects on BMD of Ca in the youngest and oldest women and life-long engagement in physical activity in older women.