This investigation provides new insight into the correlates of BMD among older African Americans. As might be expected, female gender was highly associated with lower BMD. Of importance, however, is the substantial contribution of weight to the explained variability, while age diminishes in importance after adjustment for covariates. The association of weight with BMD or fractures has been reported previously in white women. In a case control study comparing African-American and white women hospitalized for hip fractures to other hospitalized patients, Pruzansky et al. showed a comparable effect of weight in both groups. Because of the case control methodology using a comparison group of patients hospitalized for other conditions, it is impossible to estimate the effect of weight on the risk of hip fracture from that study. A report from Rochester, MN looking at a smaller, younger population of African Americans, Caucasians and recent immigrants from Somalia similarly found that weight was the major predictor of bone density in all races.

The correlation coefficients calculated independently for height, weight and BMI support associations of all three with BMD. When height and weight are entered in the same model, height loses its importance. It appears that weight by itself is more important. It is not the ratio of height and weight, that is to say “leanness,” that is associated with low BMD but being lighter. Thus, a tall, thin black individual and a short, obese black individual with identical weights would carry similar risks of having a low BMD. For men in the adjusted model, weight explained more than 27% of BMD for the total hip, compared to 21.0% for women. Self-reported health, a variable that has been previously shown to be associated with multiple outcomes in CHS, showed small associations with BMD. This makes it unlikely that weight is simply a proxy for poor health. canadian antibiotics

There are a number of pathways that may help to explain the associations of weight and BMD. The use of DXA to evaluate areal BMD clearly is artifactual, but it is the method used currently in clinical practice. After the fact, we tested to see if the percent body fat, which is available from the DXA measurements, might offer a partial explanation of the association of weight and BMD. Accepting that a clinician would not have this information prior to obtaining a DXA, we found a significant correlation in women between total hip BMD and percent body fat (p<0.001). The association with lumbar spine (p=0.039) and total body (p=0.212) BMD were not considered significant in this exploratory investigation. In men, there was limited association (p=0.029 for total hip, p>0.1 for spine and total body). When percent body fat was tested with the other significant variables in the regression models for total hip BMD, it did not enter the model. Thus, percent body fat may be of scientific interest but is of less clinical importance for selecting patients to screen for osteoporosis.

A simplistic explanation for the association of weight with total hip BMD, regardless of height or percent body fat, may be the effect of weight on skeletal loading. Consistent with the theory that bone strain from mechanical load increases bone strength and mass, the daily stress of carrying more weight may result in greater BMD in locations that feel the pressure.

In this cross-sectional analysis increasing age over the age of 64 had a significant but minor association with lower BMD. In the fully adjusted model for men, higher age did not show a significant association with BMD, and in women minor significant association was only shown for the total hip. This suggests that clinicians will gain little by waiting for individuals to age past 64 to measure bone densities. We have previously shown an association of depression with low BMD in the CHS cohort. In the smaller African-American cohort, the correlation did not reach statistical significance. antibiotics online pharmacy

There are a number of limitations inherent to this study. Although some previously reported correlates of BMD in whites were not found to be statistically significant in the fully adjusted models for African Americans, the lack of association may reflect inadequate statistical power to detect such correlations due to the relatively small number of African-American participants in the CHS. Had the sample been 10 times larger and the same relationships maintained between BMD and steroid use, the association might have been significant. This points to the need for a study in a larger population. Few of the women used estrogen (12%), which may have blunted our ability to demonstrate an association with BMD. The analyses were cross-sectional, precluding our ability to assess cause and effect. We were only able to investigate the surrogate end point of BMD instead of fractures. Further research, therefore, is required to gain insight into the causal pathway to osteoporotic fractures in black men and women.

The fact that the correlations, which are demonstrated in pair-wise analyses, are as weak as they are suggests that in this older African-American population, factors, such as smoking, physical activity and ethanol use, may not be important correlates of BMD in contrast to whites. One major risk factor that needs to be appreciated in clinical practice appears to be the association of low weight with low BMD in African Americans. The strong correlation of low weight with low BMD requires further investigation to see if it translates into increased fractures in lighter-weight African Americans. Until confirmatory data on risk factors for osteoporotic fractures in African Americans become available, it would seem to us prudent to include lower-weight African Americans in screening programs for osteoporosis.
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