Associations between adverse social position and bone mineral density in women aged 50 years or older: data from the Manitoba Bone Density Program

We examined the independent contribution of income to low bone mineral density in women aged 50 years and older. A significant dose-response association was observed between low income and low (bone mineral density) BMD, which was not explained by clinical risk factors or osteoporotic treatment in the year prior. The association between social disadvantage and osteoporosis is attracting increased attention; however, little is known of the role played by income. We examined associations between income and bone mineral density (BMD) in 51,327 women aged a parts per thousand yen50 years from Manitoba, Canada. Low BMD was defined as a T-score a parts per thousand yen2.5SD (femoral neck or minimum) measured by dual energy X-ray absorptiometry (DXA) 1996-2001. Mean household income was extracted from Canada Census 2006 public use files and categorized into quintiles. Age, weight and height were recorded at time of DXA. Parental hip fracture was self-reported. Diagnosed comorbidities, including osteoporotic fracture and rheumatoid arthritis, were ascertained from hospital records and physician billing claims. Chronic obstructive pulmonary disease was used as a proxy for smoking and alcohol abuse as a proxy for high alcohol intake. Corticosteroid use was obtained from the comprehensive provincial pharmacy system. Logistic regression was used to assess relationships between income (highest income quintile held as referent) and BMD, accounting for clinical risk factors. Compared to quintile 5, the adjusted odds ratio (OR) for low BMD at femoral neck for quintiles 1 through 4 were, respectively, OR1.41 (95 %CI 1.29-1.55), OR1.32 (95 %CI 1.20-1.45), OR1.19 (95 %CI 1.08-1.30) and OR1.10 (95 %CI 1.00-1.21). Similar associations were observed when further adjustment was made for osteoporotic drug treatment 12 months prior and when low BMD was defined by minimum T-score. Lower income was associated with lower BMD, independent of clinical risk factors. Further work should examine whether lower income increases the likelihood of treatment qualification.