Introduction: Adolescents with anorexia nervosa (AN) have low bone mineral density. However, the effect of disease recovery on (i) bone density measures assessed using the Molgaard approach, which differentiates between reported low bone density resulting from short bones (based on height Z-scores), versus that resulting from \'thin' bones [based on measures of bone area (BA) for height], or \'light' bones [based on measures of bone mineral content for bone area (BMC for BA)] and (ii) height adjusted bone density measures has not been well characterized. We hypothesized that menstrual recovery and weight gain (10% increase in BMI) would predict an increase in these measures of bone density.

Methods: In a prospective observational study, lumbar and whole body (WB) bone density were measured at 0, 6 and 12 months in 34 AN girls 12–18 yo and 33 controls. Using Ward's modification of the Molgaard approach, we determined measures of bone mineral content (BMC) for bone area (BA) and BA for height at the lumbar spine and WB, and also determined spine bone mineral apparent density (BMAD) and WB BMC adjusted for height.

Results: Girls with AN had lower spine BMC for BA Z-scores (p=0.0009), and lower WB BA for height Z (p<0.0001) compared with controls. Menstrual recovery and weight gain in AN (AN-Recovered) (median: 9 months), resulted in a stabilization of BMD measures, whereas BMD continued to decrease in AN who did not gain weight and recover menses (AN-Not Recovered). AN-Recovered also predicted greater increases in spine BMC for BA and WB BA for height compared with AN-Not Recovered (p<0.05).

Conclusions: Even short-term weight gain with menstrual recovery is associated with a stabilization of BMD measures.