Determinants of bone mineral density in older men and women: Body composition as mediator

This study aimed to assess the relative importance of several determinants of bone mineral density (BMD) and to examine to what extent these potential determinants influence total hip BMD through body composition. The study p opulation consisted of 522 participants (264 women and 258 men) of the Long itudinal Aging Study Amsterdam (LASA), aged 65 years and over, and living i n Amsterdam and its vicinity. BMD of the total hip was measured using dual- energy X-ray absorptiometry (DXA). Potential determinants of BMD were age, weight change since age 25 years, lifestyle factors, chronic diseases, medi cation use, and hormonal factors. Potential mediators between the possible determinants and BMD were two measures of body composition: fat mass (FM) a nd appendicular muscle mass (AMM). Multiple regression analyses including a ll potential determinants in one model without body composition identified age, weight change, walking activity, and sex hormone-binding globulin (SHB G) as independent determinants for total hip BMD in women. In men, current smoking, participation in sports, and parathyroid hormone (PTH) concentrati on were independently associated with total hip BMD. When total hip BMD was regressed on the potential determinants and each measure of body compositi on, it appeared that FM, and to a lesser extent, muscle mass (MM), were ind ependently related to BMD. In women, adjustment for FM reduced the strength of the associations of weight change, walking activity, and SHBG with tota l hip BMD. Adjustments for MM did not influence the associations between th e determinants and BMD. In men, neither FM nor MM appeared to play a mediat ing role between the determinants and BMD. It can be concluded that (1) FM and MM are strong independent determinants of total hip BMD and that (2) FM possibly plays a mediating role in the association of weight change, walki ng activity, and SHBG with total hip BMD in women.