Bone metabolism in adolescent boys with anorexia nervosa

Abstract

Background: Anorexia nervosa (AN) is a condition of severe undernutrition associated with low bone mineral density (BMD) in adolescent females with this disorder. Although primarily a disease in females, AN is increasingly being recognized in males. However, there are few or no data regarding BMD, bone turnover markers or their predictors in adolescent AN boys.

Hypotheses: We hypothesized that BMD would be low in adolescent boys with AN compared with controls associated with a decrease in bone turnover markers, and that the gonadal steroids, testosterone and estradiol, and levels of IGF-I and the appetite regulatory hormones leptin, ghrelin, and peptide YY would predict BMD and bone turnover markers.

Methods: We assessed BMD using dual-energy x-ray absorptiometry and measured fasting testosterone, estradiol, IGF-I, leptin, ghrelin, and peptide YY and a bone formation (aminoterminal propeptide of type 1 procollagen) and bone resorption (N-telopeptide of type 1 collagen) marker in 17 AN boys and 17 controls 12-19 yr old.

Results: Boys with AN had lower BMD and corresponding Z-scores at the spine, hip, femoral neck, trochanter, intertrochanteric region, and whole body, compared with controls. Height-adjusted measures (lumbar bone mineral apparent density and whole body bone mineral content/height) were also lower. Bone formation and resorption markers were reduced in AN, indicating decreased bone turnover. Testosterone and lean mass predicted BMD. IGF-I was an important predictor of bone turnover markers.

Conclusion: AN boys have low BMD at multiple sites associated with decreased bone turnover markers at a time when bone mass accrual is critical for attainment of peak bone mass.

Figure 1

Bone density in adolescent boys with anorexia nervosa and controls. Bone density at the lumbar spine, total hip, and its subregions (femoral neck, trochanter, intertrochanteric region) and the whole body was significantly lower in boys with AN than in controls. *, P < 0.05; **, P < 0.01.

Figure 2

Bone turnover markers in adolescent boys with AN and controls. Levels of PINP (a bone formation marker) and NTX (a bone resorption marker) were significantly lower in boys with AN than controls, suggestive of a reduced state of bone turnover. *, P < 0.05. BCE, Bone collagen equivalent.

Figure 3

Predictors of bone density in adolescent boys with AN and in controls. Lean body mass and testosterone levels were independent predictors of lumbar bone density measures, whereas BMI was the most significant and independent predictor of bone density at the hip. Lean mass predicted whole-body BMD and bone mineral content adjusted for height.