Vitamin D level in patients with systemic lupus erythematosus: its relationship to disease course and bone mineral density

Abstract

Objective To determine vitamin D levels in patients with SLE and evaluate their relationship to bone mineral density (BMD) and the disease course. Methods The study included 101 patients with SLE and 29 individuals in the control group. The study participants were tested for vitamin D level, erythrocyte sedimentation rate (ESR), C reactive protein (CRP), interleukin (IL)-6, osteocalcin (OC) and collagen type I C-terminal telopeptide (CTX), and the dual-energy X-ray absorptiometry was provided to assess BMD in the lumbar spine and the hip. Results The mean serum vitamin D level was 18.98±0.88 ng/mL, and women had 25.42% lower vitamin D levels than men (p<0.05). There was no correlation between vitamin D levels and patient's age or disease course. There was a significant inverse correlation between vitamin D levels and cumulative dose of glucocorticoids (r=-0.26) and serum inflammatory markers, particularly CRP (r=-0.39), IL-6 (r=-0.37) and ESR (r=-0.15). Vitamin D level was associated with the bone turnover markers (BTMs). In women of reproductive age with vitamin D deficiency, BMD of the lumbar spine and the hip was 9.5-23.1% higher than in those with no vitamin deficiency, respectively, and the mean lumbar spine Z-score in women of reproductive age with vitamin D insufficiency and deficiency was significantly 2.0 and 2.9 times lower than in patients with normal vitamin D level. Conclusions Hypovitaminosis D is quite common in patients with SLE and is associated with high inflammatory activity (SLE Disease Activity Index, ESR, CRP, IL-6), severity of organ damage (Damage Index), cumulative dose of glucocorticoids, BTM changes (decrease in OC, increase in CTX) and BMD decline. Vitamin D status was not associated with the patient's age or disease course.