Narrowband UVB Treatment Increases Serum 25-Hydroxyvitamin D Levels in Patients With Chronic Plaque Psoriasis

Psoriasis is a chronic, inflammatory, T-cell–mediated skin disease. Phototherapy, which consists of light used at various wavelengths, is a well-established treatment method for psoriasis vulgaris. Although successful results have been obtained with phototherapy in psoriasis, its mechanism of action is not fully understood. UV light has been shown to have an effect on T-lymphocyte function as well as various components of the natural and acquired immune response. It also has a suppressive effect on the immune system caused by many independent effects.¹ Phototherapy currently is available using broadband UVB (290–320 nm), narrowband UVB (NB-UVB)(311–313 nm), 308-nm excimer laser, UVA1 (340–400 nm), psoralen plus UVA, and photopheresis.² Narrowband UVB treatment with light sources that peak at 311 to 313 nm have been used with high efficacy and a low side-effect profile, becoming the standard phototherapy method for chronic plaque-type psoriasis.³

More than 90% of vitamin D synthesis is formed in the skin following UV exposure, and the wavelengths and the solar spectrum that stimulate vitamin D synthesis have been a focus of research.⁴ 7-Dehydrocholesterol (provitamin D₃) is first converted to previtamin D₃. Although the necessary UV wavelength for previtamin D₃ synthesis is 295 to 300 nm, it is known that production stops below 260 nm and above 315 nm.^4-6 Previtamin D₃ is unstable and is quickly converted to vitamin D₃ in the skinand then to the biologically active form of 1,25-dihydroxyvitamin D₃ (calcitriol) following hydroxylation in the liver and kidneys. Calcitriol shows its effect by binding to the special nuclear receptor for vitamin D.⁷ Many tissues including the keratinocytes, dendritic cells, melanocytes, and sebocytes in the skin have been shown to possess the enzymatic mechanism necessary for 1,25-dihydroxyvitamin D₃ production. Vitamin D also is known to have paracrine, autocrine, and intracrine effects on immunomodulation, cell proliferation, differentiation, and apoptosis, in addition to its role in calcium metabolism.^5-9 Topical vitamin D and its analogues are used effectively and safely in psoriasis treatment with these effects.¹⁰ A correlation between low serum vitamin D levels and chronic inflammation severity has been shown in psoriasis patients in some studies.^11,12

In this study, we sought to evaluate the effect of NB-UVB on vitamin D status and related metabolic markers in patients with psoriasis.

Methods

This prospective, single-center study included patients living in or around Eskisehir, Turkey, who were 18 years of age or older and had been diagnosed with chronic plaque psoriasis with a psoriasis area and severity index (PASI) score of 5 or higher. Permission was granted by the local ethics committee. Patients provided written informed consent prior to enrollment. Patients were excluded if they were younger than 18 years; were pregnant or breastfeeding; stayed in open environments for more than 2 hours per day during the summer months (May through September); used drugs affecting calcium metabolism in the last 8 weeks (eg, barbiturates, anticonvulsants, corticosteroids, vitamin D supplements, bisphosphonates); used systemic treatment for psoriasis in the last 8 weeks; used phototherapy or sunbathing in the last 8 weeks; used topical vitamin D analogues in the last 4 weeks; or had a history of psoriatic arthritis and other inflammatory disorders, renal disease, known calcium metabolism disorders, granulomatous disorders, thyroid disease, diabetes mellitus, skin cancer, or abnormal photosensitivity and known lack of response or hypersensitivity to phototherapy.

Clinical Evaluation and Laboratory Studies
The participants’ age, gender, Fitzpatrick skin type, disease duration, dairy intake and vitamin supplement levels, hours of sun exposure per week, detailed medical history, and medications were obtained and documented in the medical records.

Serum 25(OH)D levels were measured using high-performance liquid chromatography/mass spectrometry, serum calcium and phosphorus levels using colorimetric analysis, serum alkaline phosphatase (ALP) levels using the enzymatic colorimetric method, and serum parathyroid hormone (PTH) levels using electrochemiluminescence at baseline and after PASI 75 was achieved with treatment. Vitamin D levels were classified in 3 groups: (1) deficient (<20 ng/mL); (2) inadequate (20–30 ng/mL); and (3) adequate (>30 ng/mL). The PASI scores at baseline and posttreatment were calculated by the same dermatologist (S.S.).

Treatment Protocol and Patient Follow-up
Narrowband UVB treatment was started at 70% of the minimal erythema dose (MED). Phototherapy was administered 3 times weekly for 6 months or until PASI 75 response was achieved. An increase of 20% to 30% from the prior dose was made according to the participants’ clinical status at each treatment session, and the dose was stabilized once the maximum dose was achieved according to skin type—up to 2000 mJ/cm² for Fitzpatrick skin types I and II, 3000 mJ/cm² for skin types III and IV, and 5000 mJ/cm² for skin types V and VI. Participants were allowed to use low- and moderate-potency topical corticosteroids and moisturizers containing urea during the course of treatment. The study physician (S.S.) clinically evaluated participants every 4 weeks for 6 months or until PASI 75 was achieved, and the clinical improvement was calculated as the percentage decrease in PASI score.

Statistical Analysis
The Shapiro-Wilk normalcy test was used for the continuous variables in the study. Variables with a normal distribution were analyzed with the paired t test and 1-way analysis of variance test and presented as mean (SD). Variables without a normal distribution were analyzed with the Wilcoxon t test and the Kruskal-Wallis test and presented as the median and 25th and 75th quartiles. The serum 25(OH)D levels were evaluated according to the seasons with the Kruskal-Wallis test. Categorical variables were expressed as frequency and percentages. The Pearson and Spearman correlation analysis and regression analysis were used to show the relationship between the variables (ie, age, Fitzpatrick skin type, PASI score, maximum NB-UVB dose, and number of sessions). The statistical significance level was set at P≤.05. Statistical analyses were performed using SPSS software version 21.