CHANGE IN BODY MASS OR BODY FAT MAY CONFOUND THE INTERPRETATION OF CHANGE IN DEXA TBMC 634

Abstract

Dual energy x-ray absorptiometry (DEXA) is widely used to measure total body bone mineral content (TBMC) and bone mineral density (BMD). Accurate measurement and interpretation of the change in TBMC and BMD in response to specific interventions such as exercise, drug therapy or calcium supplementation is important. The purpose of this study was to investigate the correlation between change in TBMC, body mass and body fat percentage in United States Naval Academy (USNA) midshipmen (midn). 74 male midn age 18.8±1.0yo and 63 female midn age 18.3±0.7yo were recruited to this study in August 1992. Midn received a total body Norland XR-26 DEXA scan each year, in a repeated measures design, until their graduation in May 1996. Mean TBMC, percent change in TBMC, percent change in body fat, the correlation between percent change in TBMC and percent change in body fat, and percent change in body mass are shown in Table 1. Change in individual midn TBMC was directional with change in percent body fat and body mass. Change in TBMC was significantly (p<.001) correlated to change in percent body fat and body mass. Miles run per week, other exercise activities or change in height were not related to TBMC. We conclude that DEXA measurement of TBMC may be confounded with change in body mass and/or change in body fat percentage. Caution should be exercised in the interpretation of an intervention therapy on change in TBMC measured by DEXA.