In the present study, we analyzed the changes of bone mineral density (BMD) among Polish women age 40-79, as a function of biological aging and body mass index (BMI) class, and compared them with the US sample (National Health and Nutrition Examination Survey III). The null hypothesis of this study was that the rate of BMD change is femoral region, age, ethnicity, and BMI dependent. The studied group was divided into 4 age decades: 40-49, 50-59, 60-69, and 70-79 and 2 BMI classes (normal: 18.5</=BMI</=24.99 and obese: BMI>24.99). Analysis of covariance technique, using a generalized linear model with age and BMI as covariates, was used for data analysis. The influence of weight, height, and BMI on BMD loss was analyzed using multivariate regression analysis. The changes in BMD of femoral neck and trochanter are congruent. BMD decrease is not only age dependent but also, for specific ethnic groups, weight, height, and BMI dependent. The obtained results indicate that the analysis of age-dependent BMD changes should be performed by means of regression analysis using a broad age range rather than an age-decade approach.