With impressive economic development, obesity has emerged as a critical public health issue in China. Recently it was reported that obesity has taken an adverse effect on osteoporosis. Because there is different body mass index (BMI) for obesity globally, studies based on BMI levels on association of obesity with osteoporosis were quite few. Therefore, we discussed the relationship of body composition with skeletal BMD according to WHO BMI and BMI on Working Group on Obesity in China (WGOC).
Methods: A total of 502 adult men aged 20-89 were enrolled as healthy subjects for osteoporosis study at Qianfoshan Hospital, Shandong University between September 2008 and August 2010. According to WHO BMI, all subjects were divided into three groups: normal weight (18.5 ≤ BMI < 25 kg/m(2), n = 202), overweight (25 ≤ BMI < 30 kg/m(2), n = 242), and obesity (BMI ≥ 30 kg/m(2), n = 58). According to WGOC BMI, normal weight (18.5 ≤ BMI < 24 kg/m(2), n = 137), overweight (24 ≤ BMI < 28 kg/m(2), n = 225), and obesity (BMI ≥ 28 kg/m(2), n = 140). Total body and regional BMD, lean mass (LM), lean body mass index (LBMI), fat mass (FM), percent body fat (%BF) and fat mass index (FMI) were measured by dual-energy X-ray absorptiometry. Age-partial Pearson correlation analyses between body composition-related parameters and BMD. Multiple regression analyses were performed to explore the associations of BMD with LM, LBMI, FM, %BF and FMI.
Results: Fat mass (FM), %BF, FMI, LM and LBMI were positively correlated with BMD at almost sites (P < 0.001) in all subjects. However, the relationship was not different among groups. LM, LBMI, FM and FMI were positively correlated with BMD (P < 0.01) in normal weight. LM and LBMI appeared significantly positive with BMD in overweight and obesity according to WHO and WGOC criteria. %BF and FMI were negative significance with BMD at total body and some regional BMD according to WHO criteria in overweight (P < 0.05). In two obese groups, %BF appeared negatively significant with BMD (P < 0.05) according to WGOC criteria, and %BF and FMI appeared negatively significant with BMD (P < 0.05) according to WHO criteria. In regression of independent variables as FM and LM, LM showed statistically positively significant relations with BMD at almost sites (P < 0.05) in all groups. FM appeared positively significant with BMD in normal groups and overweight group according to WGOC criteria. In regression of independent variables as %BF and FMI, %BF and FMI appeared statistically negatively significant relations with BMD in overweight and obesity, but %BF and FMI were inconsistent in same site.
Conclusions: Lean mass (LM) and LBMI could help to determinant of BMD, and %BF and FMI were adverse to BMD in overweight and obesity. Comparing with two criteria, we found the differences in fat-related parameters and BMD according to WHO criteria were more obvious than that according to WGOC criteria. We also found that %BF and FMI were useful to research the relationship between osteoporosis and obesity at the same time.
Keywords: Bone mineral density; Fat mass; Fat mass index; Lean body mass index; Lean mass; Men–body mass index; Obesity; Percent body fat.