Section V: Bone Patho-Physiology Lower Fibroblast Growth Factor 23 Levels in Young Adults With Crohn Disease as a Possible Secondary Compensatory Effect on the Disturbance of Bone and Mineral Metabolism Konstantinos A. Oikonomou, 1,2 Timoklia I. Orfanidou, 2 Marianna K. Vlychou, * ,3 Andreas N. Kapsoritakis, 1 Aspasia Tsezou, 2,4 Konstantinos N. Malizos, 2,5 and Spyros P. Potamianos 1 1 Department of Gastroenterology, Faculty of Medicine, School of Health Sciences, University of Thessaly, Larissa, Greece; 2 Institute for Biomedical Research & Technology (BIOMED), Centre for Research and Technology-Thessaly (CERETETH), Larissa, Greece; 3 Department of Radiology, Faculty of Medicine, School of Health Sciences, University of Thessaly, Larissa, Greece; 4 Department of Biology, Faculty of Medicine, School of Health Sciences, University of Thessaly, Larissa, Greece; and 5 Department of Orthopaedics, Faculty of Medicine, School of Health Sciences, University of Thessaly, Larissa, Greece Abstract Fibroblast growth factor 23 (FGF-23) is a bone-derived circulating phosphaturic factor that decreases serum concentration of phosphate and vitamin D, suggested to actively participate in a complex renal-gastrointestinal- skeletal axis. Serum FGF-23 concentrations, as well as various other laboratory parameters involved in bone ho- meostasis, were measured and analyzed with regard to various diseases and patients’ characteristics in 44 patients with Crohn disease (CD) and 20 healthy controls (HCs) included in this cross-sectional study. Serum FGF-23 levels were significantly lower in patients with CD (900.42  815.85 pg/mL) compared with HC (1410.94  1000.53 pg/mL), p 5 0.037. Further analyses suggested FGF-23 as a factor independent from various parameters including age (r 5 0.218), body mass index (r 5 0.115), 25-hydroxy vitamin D (r 5 0.126), para- thyroid hormone (r 5 0.084), and bone mineral density (BMD) of hip and lumbar (r 5 0.205 and r 5 0.149, respectively). This observation remained even after multivariate analyses, exhibiting that BMD was not affected by FGF-23, although parameters such as age ( p 5 0.026), cumulative prednisolone dose ( p ! 0.0001), and smoking status ( p 5 0.024) were strong determinants of BMD regarding hip. Lower FGF-23 levels in patients with bowel inflammation are accompanied but not directly correlated with lower vitamin D levels, showing no impact on BMD determination of young adults with CD. The downregulation of serum FGF-23 levels in CD ap- pears as a secondary compensatory effect on the bone and mineral metabolism induced by chronic intestinal in- flammation. Key Words: Bone homeostasis; bone mineral density (BMD); Crohn disease (CD); fibroblast growth factor 23 (FGF-23); 25-hydroxy vitamin D (25OHD). Introduction Patients with inflammatory bowel disease (IBD) are at higher risk of developing osteopenia and osteoporosis than the general population (1). Thus, a greater risk of fractures es- timated up to 40% in IBD patients has been demonstrated (2). The etiology of bone loss in IBD is multifactorial, including Received 02/19/13; Accepted 03/27/13. *Address correspondence to: Marianna K. Vlychou, MD, PhD, Department of Radiology, Faculty of Medicine, Viopolis, 41110, School of Health Sciences, University of Thessaly, Larissa, Greece. E-mail: mvlychou@med.uth.gr 177 Journal of Clinical Densitometry: Assessment & Management of Musculoskeletal Health, vol. 17, no. 1, 177e184, 2014 Ó Copyright 2014 by The International Society for Clinical Densitometry 1094-6950/17:177e184/$36.00 http://dx.doi.org/10.1016/j.jocd.2013.03.019