Relationship between body composition, body mass index and bone mineral density in a large population of normal, osteopenic and osteoporotic women

Purpose. The knowledge of factors modulating the behaviour of bone mass is crucial for preventing and treating osteoporotic disease; among these factors, body weight (BW) has been shown to be of primary importance in postmenopausal women. Nevertheless, the relative effects of body composition indices are still being debated. Our aim was to analyze the relationship between body mass index (BMI), fat and lean mass and bone mineral density (BMD) in a large population of women. Moreover, this study represents a first important report on reference standard values for body composition in Italian women. Materials and methods. Between 2005 and 2008, weight and height of 6,249 Italian women (aged 30-80 years) were measured and BMI was calculated; furthermore BMD, bone mineral content, fat and lean mass were measured by dual-energy X-ray absorptiometry. Individuals were divided into five groups by decades (group 1, 30.0-39.9; group 2, 40.0-49.9; group 3, 50.0-59.9; group 4, 60.0-69.9; group 5, 70.0-79.9). Differences among decades for all variables were calculated using a one-way analysis of variance (ANOVA) and Bonferroni test by the SPSS programme. Results. Mean BW was 66.8 +/- 12.1 kg, mean height 159.1 +/- 6.3 cm and mean BMI 26.4 +/- 4.7 kg/m(2). According to BW and BMI, there was an increase of obesity with age, especially in women older than 50 years (p < 0.001). Lean mass increased until 50 years of age but significantly decreased after this age (p < 0.001). The percentage of osteopenia and osteoporosis in the examined population was 43.0% and 16.7%, respectively. Conclusions. Our data show that obesity significantly decreased the risk for osteoporosis but did not decrease the risk for osteopenia. It is strongly recommended that a strong policy regarding prevention of osteopenia and osteoporosis be commenced. An overall examination of our results suggests that both fat and lean body mass can influence bone mass and that their relative effect on bone could be modulated by their absolute amount and ratio to total BW.