Association between vitamin D, oestradiol and interferon-gamma in female patients with inactive systemic lupus erythematosus: A cross-sectional study.

Objectives To investigate possible associations between 25-hydroxyvitamin D (25(OH)D), oestradiol (E) and IFN-gamma (IFNγ) in female patients with inactive systemic lupus erythematosus (SLE). Methods Female patients with inactive SLE and age-matched healthy controls were recruited into this cross-sectional study. Serum concentrations of 25(OH)D E and IFNγ were measured by radioimmunoassay with gamma-counters and enzyme-linked immunosorbent assay. Results 36 patients and 37 controls were enrolled. In patients with SLE, the concentration of 25(OH)D was lower and E was higher compared with controls. In vitamin D deficient (i.e., 25(OH)D≤20 ng/ml) patients, IFNγ was 150% higher compared with patients with 25(OH)D>20 ng/ml and controls. The concentration of E was higher in all patients compared with controls independently of the vitamin D level. A difference was found between patients and controls in the correlation of 25(OH)D with E and a positive correlation was found between E and IFNγ in all participants. Conclusions Our results suggest that E may have a strong modulating effect on vitamin D function which is significant only at low concentration of E.