Low levels of vitamin D have been associated with several autoimmune disorders including multiple sclerosis, rheumatoid arthritis, type 1 diabetes and systemic lupus erythematosus (SLE). The major source of vitamin D is sunlight but exposure of SLE patients to UV rays has been shown to exacerbate disease pathology. Studies in various populations have shown an association between low vitamin D levels and higher SLE disease activity.
We enrolled 129 patients who fulfilled American College of Rheumatology criteria in the study. There were 79 treatment-naïve cases and 50 patients who were under treatment for underlying SLE. There were 100 healthy subjects from similar geographical areas included as controls. Plasma 25-OH vitamin D₃ and interferon (IFN)-α levels were quantified by enzyme-linked immunosorbent assay (ELISA). The gene expression level of IFN-α was determined by quantitative real-time reverse transcriptase polymerase chain reaction (RT-PCR).
Plasma 25-OH vitamin D₃ significantly correlated in an inverse manner with systemic lupus erythematosus disease activity index (SLEDAI) scores (P <0.0001, r = -0.42), anti-dsDNA (P <0.0001, r = -0.39), plasma IFN-α (P <0.0001, r = -0.43) and levels of IFN-α gene expression (P = 0.0009, r = -0.45). Further, plasma levels of IFN-α positively correlated with gene expression of IFN-α (P <0.0001, r = 0.84). Treatment-naïve SLE patients displayed significantly higher plasma levels of IFN-α compared to patients under treatment (P <0.001) and controls (P <0.001).
These results suggest an important role of vitamin D in regulating disease activity in SLE patients and the need to supplement vitamin D in their treatment.