Body composition in normal and osteoporotic women

Body composition and bone mineral density using dual-energy X-ray absorptiometry (DEXA) was determined in a large group of normal women and osteoporotic patients with atraumatic vertebral fractures. Between the third and seventh decades, there was an increase of 9.5 kg of body weight and 7.5 kg of fat mass in the normal women. The percentage of fat augmented from 33% to 42%. However, the lean mass showed no modifications over these decades. Fat mass in the osteoporotic women was significantly less than that in the age and sex matched controls (22.4 +/- 1.0 vs 26.6 +/- 1.0 kg; p < 0.006). However, lean tissue mass was similar in the two groups. The decrease in fat mass explain 74% of the difference of body weight between osteoporotics and controls. The fat mass of 13 osteoporotic patients (30%) was lower than the lowest value found in the controls and 20(45%) were lower than minus one standard deviation of the values for controls. The osteoporotic patients had less fat mass in the three subregions evaluated, but the difference was more significant in the trunk (-18%) and legs (-17%) than in the arms (-11%). Fat mass may have an important protective effect on the skeleton. The mechanism has yet to be elucidated.