Anorexia nervosa, obesity and bone metabolism

Abstract

Anorexia nervosa and obesity are conditions at the extreme ends of the nutritional spectrum, associated with marked reductions versus increases respectively in body fat content. Both conditions are also associated with an increased risk for fractures. In anorexia nervosa, body composition and hormones secreted or regulated by body fat content are important determinants of low bone density, impaired bone structure and reduced bone strength. In addition, anorexia nervosa is characterized by increases in marrow adiposity and decreases in cold activated brown adipose tissue, both of which are related to low bone density. In obese individuals, greater visceral adiposity is associated with greater marrow fat, lower bone density and impaired bone structure. In this review, we discuss bone metabolism in anorexia nervosa and obesity in relation to adipose tissue distribution and hormones secreted or regulated by body fat content.

Figure 1

Z scores for lumbar spine, hip, and femoral neck bone mineral density (BMD) in girls with anorexia nervosa (AN) (black bars) and healthy control subjects (white bars). Girls with AN had significantly lower Z-scores at each site than healthy adolescents. *P< .01; **P ≤ .001. From Misra et al. Pediatrics 2004;114:1574–1583 Copyright © 2004 by the American Academy of Pediatrics.

Figure 2

Change in lumbar bone mineral apparent density (BMAD) and whole body bone mineral content/height (WB BMC/Ht) measures in anorexia nervosa (AN)-not recovered (black bars), AN-recovered (gray bars), and healthy adolescents (white bars) over 1-year. AN-not recovered continued to lose bone mass over the 1-year follow-up period, and change in bone density measures was significantly lower in this group compared with controls (Tukey-Kramer test for multiple comparisons). AN-recovered did not differ from controls for change in bone density parameters and differed significantly from AN-not recovered for change in whole body bone density Z-scores. *, P <0.05. From Misra et al. J Clin Endocrinol Metab 2008;93: 1231–1237. Copyright © 2008 by The Endocrine Society.

Figure 3

Pathophysiology contributing to impaired bone metabolism in adolescents and adults with anorexia nervosa (AN); GH: growth hormone, IGF-1: insulin like growth factor-1, PYY: peptide YY. From Misra and Klibanski. Current Opinion in Endocrinology, Diabetes & Obesity 2011, 18:376–382. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins 1752-296X