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Does anorexia affect girls’ and boys’ bones differently? Probably not.

skeleton-diagramOne serious consequence of anorexia nervosa is that it hurts patients' bones. Calcium plays key roles in muscle contraction, transmission of nerve impulses and many other biological processes. We can't live without it, so to keep up with the demand for calcium in a malnourished person with an eating disorder, the body pilfers its own stores, weakening the bones. Extensive evidence shows that girls with anorexia can lose a lot of bone mass, putting them at risk for osteoporosis (link to pdf) later on.

But until now the picture for anorexic boys has been less clear. Only about 10 percent of anorexia patients are male -- though the number is rising -- and that makes them less likely to be studied.

In a new study published recently in the International Journal of Eating Disorders, a team of Stanford researchers asked whether anorexia nervosa might affect boys' bones differently. The sex hormones estrogen and testosterone have distinct effects on bone health, and teen boys generally have larger bones than girls, so it made sense to ask if, for instance, different bone sites might be more or less prone to mineral loss in adolescent boys with the disease. The researchers also wanted to know how fast problems with bone mineral density develop in boys with anorexia; other work had shown bone deficits in men diagnosed with anorexia for a while, but it wasn't clear what happened in boys who had been ill for shorter periods.

The scientists compared bone mineral density measurements from 25 boys and 253 girls who were treated by the Comprehensive Eating Disorders Program at Lucile Packard Children's Hospital Stanford between March 1997 and February 2001. Most patients were between 14 and 17 years old, and most had been ill for months, not years. DXA bone scans let the research team analyze patients' total body bone density and also focus on the hip, the femur and the lumbar spine.

After adjusting for patients' body mass index, age, and duration of illness, the researchers did not find any differences in bone mineral density between boys and girls at any sites. In both sexes, the main factor affecting bone density was the degree of malnutrition; the more malnourished the patient, the worse off were his or her bones. More female patients than males had abnormally low bone density at the femur, but this seemed to be explained by greater malnutrition, not sex differences.

"Since degree of malnutrition was the most significant predictor of bone deficits at all sites, clinicians may consider a DXA scan to evaluate for low bone mineral density and potential increased fracture risk in the most severely malnourished patients with anorexia nervosa," the researchers write in their paper. "In addition ... restoration of weight may be essential to improve bone density."

Previously: Families can help their teens recover from anorexia, new study showsA growing consensus for revamping anorexia nervosa treatment and How anorexia is striking what many consider to be an unlikely group: boys and young men
Photo by University of Liverpool Faculty of Health & Life Sciences

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