Vitamin D Status in Patients With Chronic Plaque Psoriasis

P. Gisondi; M. Rossini; A. Di Cesare; L. Idolazzi; S. Farina, G. Beltrami; K. Peris; G. Girolomoni

Disclosures

The British Journal of Dermatology. 2012;166(3):505-510. 

In This Article

Materials and Methods

Patients

This was a cross-sectional study including 145 adult patients with chronic plaque psoriasis (i.e. cases), 112 patients with RA and 141 healthy controls. Patients with psoriasis were recruited from those consecutively attending the outpatient clinic of the Dermatology Section of the University Hospital of Verona (Verona, Italy) and of the University Hospital of L'Aquila over a period of 1 year (from December 2009 to December 2010). Healthy controls were recruited from the partners or relatives of patients if not affected by psoriasis, in order to minimize the differences due to dietary intake of vitamin D. Patients with RA were recruited from those consecutively attending the outpatient clinic of the Rheumatology Section of the University Hospital of Verona. The rationale for including patients with RA is to have a control with another chronic immune-mediated inflammatory disease that has already been associated with vitamin D deficiency. Consequently, patients with RA represent a 'positive' control, other than a healthy population ('negative' control). The diagnosis of RA was confirmed by an experienced rheumatologist according to the 1987 American College of Rheumatology revised criteria.[12] The inclusion criteria for the patients with psoriasis were a clinical diagnosis of chronic plaque psoriasis (i.e. lasting at least 6 months) independently of the actual Psoriasis Area and Severity Index (PASI) score; and the absence of systemic or topical antipsoriatic treatments, including phototherapy and/or topical vitamin D derivatives, for at least 3 months before study investigations. Cases and controls were recruited if aged > 18 years. Patients with other types of psoriasis (guttate, erythrodermic and pustular psoriasis), those with concomitant inflammatory bowel diseases (i.e. Crohn disease and ulcerative colitis) and those receiving therapeutic interventions that might influence vitamin D status, including bisphosphonates, systemic corticosteroids, vitamin D and calcium supplements, were excluded. All the subjects were white skinned.

Clinical Evaluation

All subjects were interviewed and examined to collect age, sex, body mass index (BMI), alcohol consumption and smoking habit data. Alcohol consumers were defined as those who were used to consuming alcohol on a daily basis. Current smokers were defined as participants who smoked cigarettes daily or who had stopped smoking < 5 years before enrolment in the study. Nonsmokers were participants who had smoked < 5–10 packs of cigarettes during their lifetime or who had stopped smoking > 5 years before the enrolment. BMI was calculated as weight (kg) divided by height (m) squared. Psoriasis-related variables included disease duration and severity according to the PASI and the presence of psoriatic arthritis (PsA). The presence of PsA was diagnosed according to the CASPAR criteria.[13] Patients with psoriasis were defined as having diabetes mellitus if they were taking hypoglycaemic medications or if a physician had ever told them that they had diabetes. Cases and controls were interviewed about the use of drugs affecting bone metabolism, including bisphosphonates, corticosteroids, calcium and vitamin D supplements. Exposure to sunlight from March to September (sun-exposure time) was quantified as < 10, 10–20, 20–30 or > 30 min daily.[14] Patients and controls were asked to complete a diary card in each season.

Laboratory Assessment

One serum sample was collected from each subject. Four aliquots were mailed on dry ice to the laboratory of the University of Verona and kept at −80 °C until measurement of parathyroid hormone (PTH), 25(OH)D and calcium using commercial enzyme-linked immunosorbent assay (ELISA) kits (IDS, St Joseph, MI, U.S.A.) with interassay coefficient of variation ranging from 5% to 15%. Patients were diagnosed as having vitamin D deficiency when serum level of 25(OH)D was measured as < 20 ng mL−1 or 50 nmol L−1. The serum 25(OH)D level is the best indicator of overall vitamin D status because this measurement reflects total vitamin D from dietary intake and sunlight exposure, as well as the conversion of vitamin D from adipose stores in the liver.[1] C-reactive protein (CRP) was measured by a Behring nephelometer (Messer Grisheim GmbH, Bad Soden, Germany). Spring was defined as the time of the year ranging from 21 March to 20 June; summer from 21 June to 22 September; autumn from 23 September to 20 December and winter from 21 December to 20 March. Sixty-five out of 145 (47%) patients with psoriasis were sampled in spring, 30 (21%) in summer, 24 (16%) in autumn and 24 (16%) in winter. Healthy controls and patients with RA were sampled at approximately the same time as the patients with psoriasis, without significant differences between the proportions of patients sampled in the four seasons.

Statistical Analysis

All analyses were performed using STATA 10.0 (StataCorp LP, College Station, TX, U.S.A.) and GraphPad 4.0 (GraphPad Software, San Diego, CA, U.S.A.). Data are expressed as mean (SD) or percentages. Skewed variables were logarithmically transformed to improve normality for statistical purposes and then back-transformed to their natural units for presentation in tables and figures. Statistical analyses included ANOVA (for continuous variables) and χ2-test with the Yates correction for continuity (for categorical variables). The Pearson test was used to explore the linear correlation between PASI and 25(OH)D serum levels. Independence of the association of vitamin D deficiency and presence of psoriasis was assessed by multivariate regression analysis. In the fully adjusted regression model, age, sex, smoking habit, BMI, psoriasis, psoriasis duration and PASI score were also included as independent covariates. A P-value < 0·05 was considered statistically significant.

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