Journal of Cutaneous Medicine and Surgery 1–4 © The Author(s) 2015 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/1203475415622207 jcms.sagepub.com Introduction Psoriasis is a chronic inflammatory disease mediated by the innate and acquired immune systems (T lymphocytes). 1 There is evidence that vitamin D has immunomodulatory actions by enhancing innate immune system function and modulating the adaptive immune system. It induces production of cathe- licidin in keratinocytes, inhibits the development of T helper 1 cells, induces T helper 2 cell pathways, induces B cell apop- tosis, inhibits B cell maturation, and produces T regulatory cells by dendritic cells. 2-4 Previous studies have proposed the role of vitamin D deficiency in some autoimmune diseases, such as multiple sclerosis, rheumatoid arthritis, systemic lupus erythematous, and Crohn’s disease. 4,5 Vitamin D also directly regulates the proliferation and growth of keratino- cytes via vitamin D receptors. 6 There are several pathways for the effect of vitamin D deficiency in psoriasis pathogenesis: loss of antiproliferative, anti-inflammatory, and antiangio- genic activities. 7 Psoriasis is an autoimmune disease medi- ated by T helper 1 and T helper 17 pathways. Several studies have shown the efficacy of narrow-band ultraviolet B (NB-UVB) in parallel with elevation of serum vitamin D in the treatment of plaque psoriasis, which has improved researchers’ opinions regarding the effect of systemic vitamin D on psoriasis. 8-13 Another study showed that baseline levels of CYP27A1 and CYP27B1 enzymes (involved in vitamin D metabolism) in skin biopsies of psoriatic lesions were lower than those in normal skin from healthy people. 12 Given this evidence, there may be a role for vitamin D in the pathogenesis of psoriasis. Gisondi et al, 14 Orgaz-Molina et al, 15 and Gutte and Pahuja 16 have shown vitamin D deficiency to be more prevalent in patients with psoriasis than healthy individu- als in Italy, Spain, and India, respectively. In this study, we aimed to evaluate serum vitamin D levels of psoriatic patients and compare them with levels in healthy controls. Article 622207CMS XX X 10.1177/1203475415622207Journal of Cutaneous Medicine and SurgeryMaleki et al research-article 2015 1 Cutaneous Leishmaniasis Research Centre, Department of Dermatology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran 2 Cutaneous Leishmaniasis Research Centre, Department of Pathology, Mashhad University of Medical Sciences, Mashhad, Iran 3 Department of Biostatistics and Epidemiology, Mashhad University of Medical Sciences, Mashhad, Iran Corresponding Author: Yalda Nahidi, Cutaneous Leishmaniasis Research Centre, Department of Dermatology, Imam Reza Hospital, Mashhad University of Medical Sciences, Mashhad, Iran Email: nahidiy@mums.ac.ir Serum 25-OH Vitamin D Level in Psoriatic Patients and Comparison With Control Subjects Masoud Maleki 1 , Yalda Nahidi 1 , Sahar Azizahari 1 , Naser Tayyebi Meibodi 2 , and Ali Hadianfar 3 Abstract Background: Vitamin D has been shown to have immunomodulatory effects, and previous studies have proposed a role of vitamin D deficiency in multiple autoimmune diseases, including psoriasis. Objectives: The aim of this study was to investigate serum vitamin D levels in psoriatic patients and compare them with levels in controls. Methods: This study was carried out in 50 psoriasis patients. Serum vitamin D was measured by enzyme-linked immunosorbent assay. Results: The mean serum vitamin D levels in psoriatic patients and controls were 14.92 ± 6.31 and 12.52 ± 4.54 ng/mL, respectively. The difference was not statistically significant (P = .06). The prevalence of vitamin D deficiency (<20 ng/mL) was 84.0% in psoriatic patients and 93.0% in controls (P = .21). Conclusions: Most of the patients with psoriasis had vitamin D deficiency, which may have contributed to the evolution of their psoriasis. However, considering the high prevalence of vitamin D deficiency in Iran, no difference was noted between the psoriatic patients and the controls. Keywords psoriasis, serum vitamin D, Psoriasis Area and Severity Index (PASI)