Abstract and Introduction
Background Vitamin D could have important immunomodulatory effects in psoriasis.
Objectives To measure 25-hydroxyvitamin D [25(OH)D], parathyroid hormone (PTH) and calcium serum levels in patients with psoriasis and the associations with some relevant clinical features.
Methods A cross-sectional study was conducted over 1 year including 145 patients with chronic plaque psoriasis, 112 patients with rheumatoid arthritis (RA) and 141 healthy controls. 25(OH)D, PTH and calcium serum levels were measured in a centralized laboratory. Demography, comorbidities, disease severity and exposure time to sunlight (which was derived by questionnaire) were collected.
Results The prevalence of vitamin D deficiency [25(OH)D levels < 20 ng mL−1] in patients with psoriasis was 57·8% vs. 37·5% in patients with RA and 29·7% in healthy controls (P < 0·001). In winter, the prevalence of vitamin D deficiency rose to 80·9% in patients with psoriasis, to 41·3% in those with RA and to 30·3% in healthy controls (P < 0·001). Patients with psoriasis or psoriatic arthritis did not differ in 25(OH)D serum levels nor in the prevalence of vitamin D deficiency. In the logistic regression analysis, vitamin D deficiency was associated with psoriasis independently of age, sex, body mass index, calcium, PTH levels and season of blood sampling. A limitation is that the study design does not allow a causal or temporal relationship between vitamin D deficiency and psoriasis to be established.
Conclusions Vitamin D deficiency may be common in patients with psoriasis, especially in winter.
Much debate has taken place over the definition of vitamin D deficiency. Most agree that a serum level of 25-hydroxyvitamin D [25(OH)D] below 20 ng mL−1 (or 50 nmol L−1) is an indication of vitamin D deficiency, which has long been recognized as a pathological condition characterized by muscle weakness, rickets or osteomalacia. Vitamin D insufficiency, characterized as a serum level of 25(OH)D ranging from 10 to 30 ng mL−1 (25–75 nmol L−1) and without overt clinical symptoms, has recently become an important medical concern. Vitamin D insufficiency is extremely common in the U.S.A. and Europe where its prevalence is estimated to be as high as 50–80% in the general population.[2–4] Defining a level of serum 25(OH)D as low or insufficient depends on the level that is defined as normal. Health authorities used different cut-offs for their definitions of sufficient and optimal status. The Institute of Medicine Committee found 20 ng mL−1 to be the level that is needed for good bone health for all individuals. Substantial evidence suggests that vitamin D plays a pivotal role in modulating dendritic cell function and regulating keratinocytes and T-cell proliferation.[6,7] Epidemiological data have also confirmed that vitamin D deficiency may be a risk for development of autoimmune diseases including rheumatoid arthritis (RA), multiple sclerosis, systemic lupus erythematosus and Crohn disease.[8–11]
In this study we estimate the prevalence of vitamin D deficiency in patients with chronic plaque psoriasis and analyse the association of vitamin D with clinical features. The results show that vitamin D deficiency may be common in patients with psoriasis, especially in winter time.
The British Journal of Dermatology. 2012;166(3):505-510. © 2012 Blackwell Publishing