Correlates of low bone density in females with anorexia nervosa

The objectives were to delineate those factors which correlate with low bone density in patients with anorexia nervosa and in turn to predict those at greatest risk for osteopenia.

Bone density was evaluated by dual energy x-ray absorptiometry in 28 postmenarchal females with anorexia nervosa who had never received hormonal therapy. Bone density results were correlated with specific historical and physical factors utilizing descriptive statistics, scatter plots, and the Spearman correlation coefficient.

Mean age was 18.6 years, mean age at menarche was 12.9 yrs, mean length of illness was 19.8 months and mean duration of amenorrhea was 13.4 months. Mean % ideal body weight was 84% at the time of bone density, 75% at minimum weight and 100% at maximum weight. Mean lumbar spine bone density was -1.69 standard deviations from the norm; mean lateral spine bone density was -1.45 standard deviations from the norm; mean femoral neck of the hip bone density was -1.18 standard deviations from the norm. There was a strong negative correlation between duration of amenorrhea and bone density at the lumbar spine (r = -0.50, p < .01) and a mild correlation at the lateral spine (r = -0.49, p < 0.05) and femoral neck (r = -0.41, p < 0.05). There was also a strong negative correlation between length of illness and bone density at the lumbar spine (r = -0.53, p < 0.01) and lateral spine (r = -0.77, p < 0.0001), and a mild correlation with the femoral neck (r = -0.48, p < 0.05). Scatter plots of lumbar bone density versus duration of amenorrhea, and versus length of illness clearly showed not only that longer duration of amenorrhea and longer length illness correlated to bone loss, but also strikingly that within a short time of being ill and amenorrheic, significant bone loss was seen. Age, and age at menarche correlated mildly with osteopenia at the lateral spine; age correlated mildly with osteopenia at the femoral neck as well. There was a trend for minimum BMI to correlate with osteopenia at the lateral spine. There were no correlations of bone density with % IBW at bone density, minimum % IBW, maximum % IBW, change in % IBW, BMI at the time of the bone density, maximum BMI or change in BMI.

Low bone density, especially in the lumbar spine, correlated with both a longer duration of amenorrhea and longer length of illness, but not with other factors, in our patients with anorexia nervosa. As many of these patients, even those with a short duration of illness and amenorrhea, were osteopenic, it is advisable to continue to perform bone density studies in all patients with anorexia nervosa, on both a clinical and research basis.