VITAMIN D STATUS AND ITS ASSOCIATION WITH MUSCLE MASS AND PHYSICAL ACTIVITY IN YOUNG ADULTS WITH JUVENILE IDIOPATHIC ARTHRITIS

Introduction. Vitamin D may serve as an indicator of general health, and a reliable relationship has been determined between its deficiency not only with bone metabolism and disease activity in patients with autoimmune disorders but also with muscle health, pain, fatigue, and reduced physical activity. Aim. To assess vitamin D status in young adults with juvenile idiopathic arthritis (JIA) and to elucidate its associations with disease activity, physical activity, and muscle-related indicators. Methods. The study included 70 young adults with JIA, with an average age of 20.0 [18.0–25.0] years. A questionnaire assessing fatigue and physical activity was administered, and dual-energy X-ray absorptiometry (DXA) was used to evaluate bone mineral density (BMD) and muscle-related indicators. The relationship between vitamin D levels and anamnesis, clinical and laboratory data, and DXA results was analyzed. The analysis was performed using the Mann–Whitney U test and the χ² test, logistic regression analysis, utilizing the R program. Results. The average vitamin D level was 44.4 ± 18.9 nmol/L. Deficiency was detected in 63% (44/70 patients) and insufficiency – in 31% of young adults with JIA (22/70 patients). Patients with low 25(OH)D level had higher disease activity according to Disease Activity Score (DAS28) and clinical Juvenile Arthritis Disease Activity Score (cJADAS27) and lower muscle-related indicators; at the same time, no differences were found depending on age, sex, erythrocyte sedimentation rate, and C-reactive protein. Low vitamin D level was associated with lower body mass index (BMI) (OR 0.81; 95% CI 0.69–0.93; р = 0.005), higher disease activity by cJADAS27 (OR 1.15; 95 % CI 1.06–1.28; р = 0.002), and lower appendicular lean mass and physical activity (OR 0.87; 95 % CI 0.78–0.96; р = 0.008; OR 0.98; 95 % CI 0.97–0.99; р < 0.001, respectively). Conclusions. Vitamin D deficiency was observed in 63% of patients with JIA. Low vitamin D levels were significantly associated with increased disease activity, decreased muscle mass indicators, and physical activity.