| Osteoporosis is a common skeletal disease characterized by a low bone mineral density (BMD) and a microarchitectural deterioration of bone tissue. The incidence of osteoporosis is the seventh in the common diseases. It is important to increase our knowledge of the pathogenesis of osteoporosis for the development of preventive strategies, because it is not a good cure for osteoporosis. The peak BMD is very important to study for prevention, diagnosis and treatment of osteoporosis. Some modifiable factors may influence BMD variation, such as body weight, body composition. Body composition consists of fat mass (FM), lean mass (LM) and bone mineral content (BMC). The relationship between body composition and bone mineral density (BMD) has been investigated in Caucasians, but few data were available in Asians such as Chinese as to, e. g., whether fat mass (FM) or lean mass (LM) contributed more significantly to BMD variation. Objects: This study the first aim is to assess the peak BMD of forearm, the peak BMD of lumbar spine, the peak BMD of hip and the peak BMD of whole body in males and in females. This study aimed secondly to assess the relative contributions of LM and FM to BMD, and, in addition, to investigate the gender-specific relationship between BMD and LM, FM in healthy Chinese adults. Methods: 878 females and 1109 males healthy Chinese subjects aged 20-45 years were recruited. BMD (g/cm2) at the forearm, the spine (L1-4), hip and whole body, FM (kg) and LM (kg) were measured by a Hologic 4500W dual-energy X-ray absorptiometry (DXA). We performed the Pearson correlation analysis and multiple regression analyses with FM and LM as independent variables and BMD as dependent variable while adjusting for age and height. Results: First, The Peak BMD is different at different sites. The Peak BMD of total forearm is 0.640 g/cm2 in males and 0.542 g/cm2 in females. The Peak BMD of lumbar spine (L1-4) is 0.978 g/cm2 in males and 0.964 g/cm2 in females. The Peak BMD of total hip is 0.993 g/cm2 in males and 0.872 g/cm2 in females. Second, LM and FM were positively associated with BMD. The effect of LM on BMD variation (7%～21%) was evidently greater than that of FM (0.08%～4%) in males.Conclusions: First, the BMD at the forearm, the spine (L1-4), hip and whole body is increasing with the age growing before the age of the peak BMD. Then the BMD at the forearm, the spine (L1-4), hip and whole body is decreasing with the age growing after the age of the peak BMD. Secondly, LM is a more important determinant of BMD than FM in healthy Changsha adults. Our inference is that physical activities or exercises that lead to more LM have beneficial effects on BMD that are overwhelmingly larger than the beneficial effects of larger FM on BMD. The adoption of a healthy lifestyle is highly encouraged to increase LM for prevention of osteoporosis and obesity.
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