The importance of body weight history in the occurrence and recovery of osteoporosis in patients with anorexia nervosa: evaluation by dual X-ray absorptiometry and bone metabolic markers

In order to investigate the risk factors, pathogenesis and natural course of the osteoporosis frequently seen in anorexia nervosa, we measured the bone mineral density (BMD) of the lumbar spine using dual X-ray absorptiometry in 51 Japanese female patients with anorexia nervosa, and followed the change in BMD of 29 patients for 11 to 46 months, We also evaluated the serum osteocalcin and the urinary CrossLaps, degradation products of collagen I, in 103 samples obtained from 51 patients. There was a significant correlation between the spinal BMD and the duration of emaciation below a body mass index (BMI) of 15 kg/m(2) (r = -0.652, P < 0.0001) and 16 kg/m(2) (r = -0.647, P < 0.0001). The increase in BMD per year in the 29 patients significantly correlated with the BMI at the time of entry of each follow-up period (r = 0.712, P < 0.0001), The critical BMI for a positive increase in BMD was 16.4 +/- 0.3 kg/m(2) (mean +/- S.E.M.). The serum osteocalcin declined, while the urinary CrossLaps increased in proportion to a decrease in BMI. Both markers were normalized in patients whose BMI was between 16.4 and 18.5 kg/m(2). The ratio of urinary CrossLaps to serum osteocalcin correlated with BMI (r = -0.664, P<0.0001). We conclude that the body weight history is the most important predictor of the presence of osteoporosis as well as of recovery. The BMD of patients does not increase to the normal range even several years after the recovery from this disorder, and they remain a high-risk group for osteoporosis in the future.