Background Vitamin D is a crucial factor in the regulation of calcium homeostasis and in the maintenance of skeletal health. There is mounting evidence that vitamin D also plays an important role in the modulation of the immune system.

Objectives The aim of this study was to assess bone mineral density (BMD), bone turnover markers and vitamin D levels in psoriatic arthritis (PsA) patients and to investigate the relationship between 25-hydroxyvitamin D (25OHD) levels and disease activity.

Methods Fifty PsA patients were recruited. Those with axial involvement were excluded.

Serum calcium, phosphorus, 25OHD, parathyroid hormone (PTH), P1NP and βCTX were measured as bone turnover markers in all patients. BMD was measured at the lumbar spine and the hip by dual X-ray absorptiometry (DXA). Disease activity was assessed using Disease Activity Score-28 (DAS-28), Bath Ankylosing Spondilitys Disease Activity Index (BASDAI) scores, C-reactive protein (CPR) as well as erythrocyte sedimentation rate (ESR) levels. The Health Assessment Questionnaire (HAQ) was applied to determine the degree of functional impairment.

Results Fifty patients were included: 12 premenopausal women, 22 postmenopausal women and 16 men. The clinical forms of PsA were: 32% oligoarticular and 54% polyarticular.

Mean disease duration was 111±108 months, mean 25OHD levels were 28,91±13,3 ng/dl, mean DAS 28 1,61±0,70 and BASDAI 3,24±1.99.

Vitamin D insufficiency (<30ng/dl) was found in 16 patients (32%). Frequency of osteoporosis was 14% and of osteopenia was 49%, being higher in postmenopausal women (75%) as compared to men (29,4%) or premenopausal women (25%). 32% of patients presented insufficient vitamin D levels (25OHD <30ng/ml) and 22% showed deficient levels (25OHD <20ng/ml). Bone remodeling markers were within normal values: P1NP 38,9 (14-72) ng/ml and βCTX 341,2 (142-866) pg/ml. Six fractures were registered.

We found inverse correlation between vitamin D levels and disease activity (ESR, CPR) and HAQ. Mean values of ESR, CPR and HAQ were 10,9±11,41 mm/h, 5,38±0,86 mg/L and 0,33±0,48 respectively, in patients with normal vitamin D levels; whereas patients with low vitamin D levels presented higher values (ESR, CPR and HAQ mean values of 12,1±9,82 mm/h, 6,48±5,38 mg/L and 0,37±0,56). Our results are not statistically significant due to low sample population.

Conclusions High prevalence of 25OHD insufficiency was found in PsA patients, despite sunlight exposure recommendations for psoriasis. Almost 63% of these patients have decreased bone mass. PsA patients presented an inverse correlation between vitamin D levels and disease activity and functional impairment. These results indicate that there is a relationship between high disease activity in PsA and vitamin D metabolism and increased bone resorption.

Disclosure of Interest None declared