Determinants of Vitamin D Levels in Children, Adolescents, and Young Adults with Juvenile Idiopathic Arthritis

Objective. Deficiency of 25-hydroxyvitamin D [25(OH) D] is reported to be common in patients with rheumatoid arthritis (RA); data in patients with juvenile idiopathic arthritis (JIA) are inconsistent. We assessed serum 25(OH) D in children, adolescents and young adults with JIA, in order to identify the risk factors for vitamin D deficiency in patients with JIA. Methods. We evaluated 152 patients with JIA: 115 female, 37 male, mean age 16.2 +/- 7.4 yrs; evaluated by onset type, 96 had oligoarticular, 35 polyarticular, 7 systemic, and 14 enthesitis-related arthritis (ERA). Patients were compared with a control group matched for sex and age. All patients and controls underwent laboratory tests of plasma 25(OH) D, parathyroid hormone (PTH), calcium, phosphorus, and bone alkaline phosphatase levels, and dual-energy x-ray absorptiometry examination. Results. Patients with JIA showed significantly reduced 25(OH) D levels compared to controls (p < 0.001), even divided into subtypes (oligoarticular, p < 0.05; polyarticular, p < 0.005; systemic, p < 0.001; ERA, p < 0.005). Patients with active disease and/or frequent relapses had significantly reduced 25(OH) D levels compared to patients with no active disease and no frequent flares (p < 0.005, respectively). Nevertheless, JIA patients had significantly higher PTH levels compared to controls (p < 0.0001). JIA patients with 25(OH) D deficiency showed a significantly lower bone mineral apparent density than those with normal 25(OH) D levels (p < 0.001). Conclusion. JIA patients have reduced 25(OH) D and higher PTH values. This may explain at least in part why JIA patients, despite more effective current drugs, do not achieve bone-normal condition over time. JIA patients with more severe disease could require higher supplementation of vitamin D to maintain normal 25(OH) D serum levels. Longterm studies are needed to investigate the relationship between serum 25(OH) D levels and disease activity in JIA.