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Objective: To assess the impact of anorexia nervosa and that of nutritional rehabilitation on bone resorption. Design: Cross-sectional, observational study. Setting: Rome, Italy Subjects: Twenty-eight female patients affected by anorexia nervosa (AN, BMI 17.0 kg=m 2 ), 18 females rehabilitated from anorexia nervosa and weight-stable for at least 6 months (RE, BMI ! 18.5 kg=m 2 ) and 34 age-and sex-matched healthy controls (CO, BMI ! 18.5 kg=m 2 ). Among AN patients, 16 were affected by the 'restrictive' (ANr) and 12 by the 'purging' type (ANp) of anorexia nervosa. Method: Body weight, height and skeletal diameters were measured on each individual. The skeletal mass (SKM) was predicted from the skeletal diameters of the elbow, wrist, knee and ankle, using the equation of Martin. Twenty-four-hour urinary excretion of pyridinium crosslinks of collagen (pyridinoline (Pyd) and deoxypyridinoline (Dpd)) and creatinine was assessed by reversed-phase HPLC with fluorimetric detection after solid-phase extraction and by the Jaffé-method with deproteinization, respectively. Results: Twenty-four-hour urinary output of Pyd and Dpd was not significantly different between AN and CO when expressed in absolute values, but AN showed higher bone resorption than CO when Pyd and Dpd excretion was adjusted by either creatinine (P < 0.0000) or the SKM (P < 0.05). Within the AN group, urinary excretion of both cross-links was significantly and consistently higher in ANp compared with ANr (P < 0.05). However, these differences disappeared when crosslink output was adjusted either by urinary creatinine or SKM. RE subjects showed no differences in bone resorption with the AN group despite weight gain, being crosslink excretion consistently elevated compared to controls (Pyd: P < 0.01 by creatinine and P < 0.05 by SKM; Dpd: P < 0.01 by creatinine and P < 0.05 by SKM). Conclusion: Bone resorption is elevated in anorexia nervosa and different strategies for low-weight maintenance do not seem to have a differential impact. Increased bone resorption persists in subjects with past diagnosis of anorexia nervosa despite rehabilitation lasting more than 6 months. This finding indicates that bone mass and turnover should be monitored in anorexia nervosa patients and ex-patients well beyond recovery of normal body mass. Further investigation is warranted to examine the long-term effect of such prolonged increase in bone turnover at a young age. Sponsorship: Dr. Valtueña is supported by a Marie Curie Fellowship from the European Commission (Contact no. HPMF-CT-1999-00192). European Journal of Clinical Nutrition (2003) 57, 260 -265. doi:10.1038=sj.ejcn.1601527 Keywords: anorexia nervosa; 'purging' anorexia; restrictive anorexia; pyridinoline; deoxypyridinoline; nutritional rehabilitation *Correspondence: F Branca, Human Nutrition Unit, National Institute for Food and Nutrition Research, Via Ardeatina 546, 00179 Roma, Italy. E-mail: f.branca@agora.it Guarantor: Dr. Francesco Branca. Contributors: SV was responsible for the analysis of the data and th...