Determinants Of Bone Mineral Density In African-american And Caucasian College-aged Women

Abstract

Historically, studies have shown that African-American (AA) women have greater bone densities (BMD) than Caucasian (CA) women. However, evidence is evolving that AA women are at risk for low BMD as are their CA counterparts. There is some debate over what accounts for the differences in BMD among AA and CA women. PURPOSE: To explain the variance in BMD in AA and CA college-aged women. A secondary purpose is to examine the prevalence of low BMD among AA and CA college-aged women. METHODS: Women (N = 101) aged 18 - 30 completed a demographic questionnaire, a 7-day Physical Activity Recall, and a four-day food log that included food intake for two weekdays and two weekend days. DXA scans of the spine, non-dominant femur, and total body were performed using a Hologic Delphi-W (Waltham, MA) DXA machine. Food records were analyzed using the Nutrition Data System for Research (NDS-R, v. 4.01). Forward multiple linear regression was performed to measure the variance in femoral and spinal bone mineral density as predicted by seven variables: race, family history of osteoporosis, length of time on oral contraceptives, average calcium intake, body mass index (BMI), hours/week of physical activity and age. RESULTS: In this sample, 35.3% of the CA participants had low spinal BMD; and 7.8% had low femoral BMD. For AA, 42% had low spinal BMD; and 8% had low femoral BMD. Only body mass index (p = 0.001) and total hours of exercise (p = 0.017) were significant predictors of spinal BMD. Similarly, BMI (p = 0.010) and total hours of exercise (p = 0.007) were significant predictors of femoral BMD. These predictors explained 14.9% of the variance in spinal BMD and 13.1% of the variance in femoral BMD. CONCLUSIONS: Race was not a significant predictor of spinal or femoral BMD. Exercise and BMI, however, were significant predictors of both spinal and femoral BMD. It is possible that the other variables were not significant in predicting BMD due to the cross-sectional nature of the study. It is also possible that race was not a significant predictor of BMD because significant racial differences in BMD do not emerge until after menopause.