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(3) (25(OH)D(3)), oestradiol (E(2)) 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(3,) E(2) 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(3) was lower and E(2) was higher compared with controls. In vitamin D deficient (i.e., 25(OH)D(3)≤20 ng/ml) patients, IFNγ was 150% higher compared with patients with 25(OH)D(3)>20 ng/ml and controls. The concentration of E(2) 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(3) with E(2) and a positive correlation was found between E(2) and IFNγ in all participants. CONCLUSIONS: Our results suggest that E(2) may have a strong modulating effect on vitamin D function which is significant only at low concentration of E(2).