Associations Between Sedentary Behaviors And Visceral Adiposity On Bone Mineral Density In Women

Abstract

American society has become increasingly sedentary putting this population at higher risks of developing chronic disease such as osteoporosis. One potential link between sedentary behaviors and risk of chronic disease progression is obesity. Studies comparing fracture incidence in obese and non-obese women have demonstrated that obesity is associated with increased risk of fracture at some skeletal sites but seems to be protective at others. Researchers have suggested that certain types of obesity may be a strong predictor of risk of osteoporosis-related non-spine fractures. PURPOSE: The purpose of this study is to examine the relationships between physical activity levels (PA), obesity and bone mineral density (BMD) in adult sedentary women. METHODS: Twenty-three women, aged 45-65, were instructed to wear an accelerometer for one week, and participate in a Dual energy X-ray absorptiometry (DXA) scan for determining BMD of the whole body (WBBMD), lumbar spine (L1-L4), femoral neck (FN) and forearm as well as body fat mass and lean mass. Participants were divided based on obesity status into two groups, high and low BMI. A one-way ANOVA analysis was used to detect differences in BMD and PA levels by group. Multiple linear regression was used to analyze the effect of PA measures and body composition on BMD. RESULTS: Light PA decreased whole body BMD (WBBMD) (β= -13.5, p=.012) while body fat percentage (BF%) and fat free mass (FFM) increased it (β=1754.7, p=.041 and β=3.558, p=.001). Light PA, BF% and FFM all yielded a higher L1-L4 lumbar spine BMD (β=-.003, p=.05, β=0.641, p=.037 and β=.001, p=.017, respectively). The higher the total amount and the longer the length of sedentary bouts increased arm BMD (β=.052, p=.038 and β=.016, p=.000). In addition, greater MET values yielded higher forearm BMD (β=6.085, p=.020). CONCLUSIONS: These results demonstrate that PA levels and fat mass have a significant effect on sedentary adult women’s bone density levels. Further investigation of causal mechanisms underlying these associations is warranted.