Event Abstract Back to Event Circulating Fibroblast Growth Factor-23 (FGF-23) following vitamin D supplementation in vitamin D insufficiency R Inaoui1*, WD Fraser2, I Fogelman1 and G Hampson1 1 Guy's Hospital, Osteoporosis Clinic, Rheumatology, United Kingdom 2 Royal Liverpool Hospital, Department of Clinical Chemistry, United Kingdom 1,25 dihydroxy vitamin D up-regulates Fibroblast Growth Factor -23 (FGF-23). Both are implicated in a feedback loop, as increases in FGF-23 inhibit 1, 25 dihydroxy vitamin D synthesis. High dose vitamin D supplements are frequently given to patients with low 25(OH) vitaminD who are at high fracture risk. We investigated the effect of high dose vitamin D on circulating FGF-23 concentrations and the interaction between FGF-23 and 1, 25 dihydroxy vitaminD in patients with vitamin D deficiency /insufficiency. Thirty one subjects (11M aged (mean [SD]) 56.6 [19.3] and 20 F aged 62.7 [15.3] years were studied. They were administered an intra-muscular injection of 300,000 I.U of Ergocalciferol (D2) and prescribed daily supplements of calcium (1.2 g) and 800 I.U colecalciferol (D3). Blood samples were obtained at baseline, 1, 2 and 3 months for measurement of serum calcium, phosphate, PTH, 25 (OH) vitamin D and FGF-23. 1,25dihydroxyvitamin D was measured at baseline and 3 months. Serum 25 (OH) vitamin D increased significantly (baseline mean [SD] 33.5 [14.9], 50.5 [21.6] nmol/L at 3 months (p < 0.05). PTH decreased from baseline, but not significantly (baseline: 64[60], 3 months: 50[28.5] ng/L). There was no significant difference in serum phosphate. FGF-23 concentrations increased significantly (baseline: 85.3[44.1], 1 month : 111[58], 2 month : 99.6 [62], 3 month: 108[59] RU/ml (p <0.05). A positive correlation was seen between FGF-23 and serum phosphate at 3 months (r= 0.44, p= 0.02). 1, 25 dihydroxyvitamin D increased in 18 patients (Group A : baseline 107 [39] , 3 month 134[34.5] pmol/L) and decreased in 13 patients (Group B : baseline 158.6 [40] , 3 months 123 [37] pmol/L p<0.05). Baseline 1, 25 dihydroxyvitamin D was significantly higher in Group B compared to Group A (p<0.001). There was no significant difference in PTH. A larger increase in FGF-23 was seen in Group B (Group B mean [SEM] % change from baseline; 1 month: 90[47], 2 month: 84[44], 3 month: 45[16], Group A; 1 month: 36[12.5], 2 month: 14 [10], 3 month: 29 [15] p=0.039). These data suggest that FGF-23 is a counter-regulatory hormone for 1, 25 dihydroxy vitamin D production. Keywords: Bones, Bone Research Conference: 2011 joint meeting of the Bone Research Society & the British Orthopaedic Research Society, Cambridge, United Kingdom, 27 Jun - 29 Jun, 2011. Presentation Type: Oral Topic: Abstracts Citation: Inaoui R, Fraser W, Fogelman I and Hampson G (2011). Circulating Fibroblast Growth Factor-23 (FGF-23) following vitamin D supplementation in vitamin D insufficiency. Front. Endocrinol. Conference Abstract: 2011 joint meeting of the Bone Research Society & the British Orthopaedic Research Society. doi: 10.3389/conf.fendo.2011.02.00029 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 30 Sep 2011; Published Online: 30 Sep 2011. * Correspondence: Dr. R Inaoui, Guy's Hospital, Osteoporosis Clinic, Rheumatology, London, United Kingdom, rachidainaoui@wanadoo.fr Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers R Inaoui WD Fraser I Fogelman G Hampson Google R Inaoui WD Fraser I Fogelman G Hampson Google Scholar R Inaoui WD Fraser I Fogelman G Hampson PubMed R Inaoui WD Fraser I Fogelman G Hampson Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.