Malnutrition Has a Primary Role in Bone Loss

Women with anorexia nervosa can develop bone loss as rapidly as 6 months after the disease begins, and the effects can remain even after weight is restored. Researchers at the Massachusetts General Hospital, Boston, and the Wilkins Center for Eating Disorders, Greenwich, CT, recently demonstrated the high prevalence and profound degree of site-specific bone loss in a group of women with anorexia nervosa (Ann Intern Med 2000;133:790). They also reported that malnutrition has a primary role in anorexia-nervosa-related bone loss, independent of estrogen deficiency. (See also September/October EDR, p.1).

The researchers recruited 130 women with anorexia nervosa for the study through ads and physician referrals. Dual-energy x-ray absorptiometry was used to determine bone mineral density (BMD) at numerous sites, including the anterior-posterior lumbar spine, lateral spine, left total hip, femoral neck, and greater trochanter. Women were also asked about use of exogenous estrogen.

Half of patients had osteopenia

More than a fourth of the group (34 patients, or 26%) had a history of fractures. Osteopenia and osteoporosis, respectively, were seen at the anterior-posterior spine in 50% and 13% of patients, at the lateral spine in 57% and 24%, and at the total hip in 47% and l6% of patients. Only 37% of patients had normal bone mineral density at the anterior-posterior spine; normal bone density at the lateral spine was noted in only 19% of patients, and of the total hip in 37% of patients. BMD was reduced by at least 1 standard deviation (SD) at one or more skeletal sites in 92% of patients.

Weight predicted BMD

Weight was a significant independent predictor of BMD at all sites. The authors also found that estrogen exposure had a minimal effect on BMD. They hypothesize that the effectiveness of estrogen in increasing or preserving BMD in women with anorexia nervosa may be undermined by continued undernutrition, which may act to uncouple bone formation and resorption. Twenty-three percent of patients were using supplemental estrogen, but current or prior use of estrogen was not associated with bone mineral density at any site. Time since the last menstrual period and the age at menarche were also significant predictive factors for BMD at the anterior posterior spine.