Vitamin D status in systemic lupus erythematosus patients and its association with selected clinical and laboratory parameters

Objectives: To identify relationships between vitamin D serum levels and the presence of autoantibodies directed against vitamin D and levels of interleukin(IL)-17 and IL-23 in patients with systemic lupus erythematosus (SLE). Methods: The study included 49 patients with SLE. Serum concentrations of 25(OH)D₃ were measured with electrochemiluminescence immunoassay (ECLIA). Enzyme-linked immunosorbent assays (ELISA) were used to determine antibodies directed against 1,25(OH)₂D₃ and levels of IL-17 and IL-23 in serum of SLE patients. In evaluation of vitamin D status, the control group consisted of 49 age and gender matched healthy individuals, whereas in assessment of anti-vitamin D antibodies the control group comprised 30 sera from blood donors. Results: Serum concentration of 25(OH)D₃ in SLE patients during the warm season was 18.47 ± 9.14 ng/ml, which was significantly decreased as compared with that of the control group – 31.27 ± 12.65 ng/ml (p = 0.0005). During the cold season a trend toward lower concentration of 25(OH)D₃ in SLE patients was revealed; however, it did not reach statistical significance (11.71 ± 7.21 ng/ml vs. 16.01 ± 8.46 ng/ml; p = 0.054). Results within the recommended range for vitamin D (30–80 ng/ml; 70–200 nmol/l) were observed only in three patients. The 25(OH)D₃ concentration was decreased in SLE patients with renal disease or leucopenia as compared with the levels in patients who did not have either problem (p = 0.006 and p = 0.047, respectively). The cold season was found to be a risk factor for vitamin D deficiency (<20 ng/ml) (odds ratio = 9.25; p = 0.005). Autoantibodies directed against 1,25(OH)₂D₃ were detected in three SLE patients. No significant difference in 25(OH)D₃ serum concentrations was found between SLE patients with and without these autoantibodies. No link was shown between the existence of autoantibodies against 1,25(OH)₂D₃ and clinical or laboratory findings, including IL-17 and IL-23 levels. However, serum concentrations of IL-23 were lower in patients with vitamin D deficiency (p = 0.037). Conclusions: SLE patients, especially those with leucopenia or renal involvement, are at high risk of vitamin D deficiency and require vitamin D supplementation. Some SLE patient sera contained 1,25(OH)₂D₃ antibodies, but these antibodies do not appear to affect vitamin D levels.