Lean body mass as a risk factor for osteoporosis in postmenopausal women

Objective: We studied the lean body mass (LBM) as a potential, easily measured prognostic factor for osteoporosis. Methods: Lean body mass was measured by bioelectrical impedance analysis and lumbar bone mineral density (BMD) with dual energy x-ray absorptiometry in 821 postmenopausal women (age 45-80 years). Patients were classified according to LBM (less than or equal to 40kg, 28%; >40-less than or equal to 45kg, 40%; >45-less than or equal to 50kg, 22%; >50kg, 10%). Contingency table analysis was performed to analyze associations between BMD, age, and risk factors for osteoporosis, particularly hormone replacement therapy (HRT). BMD values less than or equal to0.8 g/cm(2) and > 1.0 g/cm(2) were classified as low and high, respectively. Results: Among women without HRT, those with LBM less than or equal to 40 kg had a twice as high rate of low BMD than those with LBM >50 (41% vs. 19%, respectively) and a lower rate of high BMD (11% vs. 32%, respectively). Among women with >5 years of HRT, those with a LBM less than or equal to 40 kg had a similar rate of low BMD as those with a LBM >50 kg (17% and 12%, respectively). There were no significant differences in LBM according to age. There were no age-related associations with LBM in women with a fat mass >43% or less than or equal to 29 %. A history of osteoporosis was more common in women without HRT and a LBM less than or equal to 40 kg than in those with a LBW >50 kg (33% vs. 11%, respectively); in women with HRT the proportions were 29% and 19%, respectively. There was no significant correlation between LBM and physical activity. Conclusions: Measurement of LBM is useful for estimating muscle mass. A bioelectrical impedance technique is economical in time and cost and well tolerated by patients. In postmenopausal women the LBM is helpful for evaluating the risk of osteoporosis.