Research Article Vitamin D and Male Sexual Function: A Transversal and Longitudinal Study Giacomo Tirabassi , 1 Maurizio Sudano, 2 Gianmaria Salvio, 1 Melissa Cutini, 1 Giovanna Muscogiuri, 3 Giovanni Corona, 4 and Giancarlo Balercia 1 1 Division of Endocrinology, Department of Clinical and Molecular Sciences, Polytechnic University of Marche, Via Conca 71, Umberto I Hospital, 60126 Ancona, Italy 2 Diabetology and Endocrinology Unit, S. Maria della Misericordia General Hospital, Via Comandino 70, 61029 Urbino, Italy 3 I.O.S. & COLEMAN Srl, Acerra, 80011 Naples, Italy 4 Endocrinology Unit, Maggiore-Bellaria Hospital, Medical Department, Azienda USL di Bologna, Bologna, Italy Correspondence should be addressed to Giancarlo Balercia; g.balercia@univpm.it Received 8 July 2017; Revised 6 October 2017; Accepted 7 December 2017; Published 8 January 2018 Academic Editor: Maria L. Dufau Copyright © 2018 Giacomo Tirabassi et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background. The effects of vitamin D on sexual function are very unclear. Therefore, we aimed at evaluating the possible association between vitamin D and sexual function and at assessing the influence of vitamin D administration on sexual function. Methods. We retrospectively studied 114 men by evaluating clinical, biochemical, and sexual parameters. A subsample (n = 41) was also studied longitudinally before and after vitamin D replacement therapy. Results. In the whole sample, after performing logistic regression models, higher levels of 25(OH) vitamin D were significantly associated with high values of total testosterone and of all the International Index of Erectile Function (IIEF) questionnaire parameters. On the other hand, higher levels of total testosterone were positively and significantly associated with high levels of erectile function and IIEF total score. After vitamin D replacement therapy, total and free testosterone increased and erectile function improved, whereas other sexual parameters did not change significantly. At logistic regression analysis, higher levels of vitamin D increase (Δ-) were significantly associated with high values of Δ-erectile function after adjustment for Δ-testosterone. Conclusions. Vitamin D is important for the wellness of male sexual function, and vitamin D administration improves sexual function. 1. Introduction Erection is a complex phenomenon which implies a delicate and coordinated equilibrium among the neurological, vascu- lar, and the tissue compartments. Many clinical factors (e.g., age, cardiovascular risk, and smoking habit) are able to impair erectile function [1]. Vitamin D is mainly involved in the regulation of cal- cium/phosphorus homeostasis and bone health. However, animal and human studies also suggest an involvement of vitamin D in the pathogenesis of several endocrine dis- eases [2–4]. In fact, vitamin D may have a role also in type 1 and type 2 diabetes mellitus, Addison’s disease, Hashimoto’s thyroiditis, Graves’ disease, and polycystic ovary syndrome [2–4]. Some evidence also suggests a possible role for vitamin D in the regulation of sexual function. In particular, recent clinical works have suggested that low vitamin D levels may somehow be associated with the occurrence of sexual distur- bances, especially erectile dysfunction [5–8], even if not all the studies agree on this point [9]. These results need confir- mation because of their potential revolutionary approach to the treatment of sexual dysfunction. To the best of our knowledge, only three works have assessed the effect of vitamin D supplementation on sexual function, showing different results [8, 10, 11]. Hindawi International Journal of Endocrinology Volume 2018, Article ID 3720813, 8 pages https://doi.org/10.1155/2018/3720813