Body mass index is positively associated with bone mineral density in US older adults

A Summary Literature has been conflicting as to whether obesity is protective against osteoporosis. Understanding the relationship is particularly important in light of the increasing prevalence of obesity among older adults. Study results confirm a protective association between obesity and osteoporosis in a recent, nationally representative sample of US older adults. Purpose Currently, the majority of US older adults are either overweight or obese. Evidence regarding the relationship between body composition measures and bone mass is conflicting, possibly because different measures of obesity reflect multiple mechanisms. Additionally, there are important age, gender, and racial differences in a risk of osteoporosis and fat mass composition. The objective of this study was to examine the association between body mass index (BMI) and bone mineral density (BMD) in a recent, nationally representative sample of US older adults as well as to see if this relationship differs by age, sex, and race. Methods Data for this study were obtained from the National Health and Nutrition Examination Survey (2005-2008) for adults ages 50 and older (n=3,296). Linear regression models were used to predict BMD of the femoral neck (measured by dual-energy X-ray absorptiometry (DXA)) as a function of BMI (measured height and weight) and a range of study covariates. Results Every unit increase in BMI was associated with an increase of 0.0082 g/cm(2) in BMD (p<0.001). Interaction terms for BMI and age (p=0.345), BMI and sex (p=0.413), and BMI and race (p=0.725) were not statistically significant. Conclusions Study results confirm the positive association between BMI and BMD, and this relationship does not differ by age, sex, or race. A 10-unit increase in BMI (e.g., from normal BMI to obese) would result in moving an individual from an osteoporotic BMD level to a normal BMD level. Results demonstrate a protective, cross-sectional association between obesity and osteoporosis in a recent sample of US older adults.