Background: Observational studies in humans suggest an association between vitamin D deficiency and many
rheumatologic disorders. Pathophysiological investigations confirm that severe hypovitaminosis D, in genetically predisposed subjects, can impair self tolerance and immune responses by compromising the regulation of dendrite cells, regulatory Tlymphocytes, Th1 cells and B cell function. Objectives: The aim of our work was to assess Vit D level in patients with RA, SLE and Behcet's disease and to evaluate its relation to various parameters of the disease and its activity. Results: Ninety patients (20 RA, 54 SLE and 16 Behcet's disease) were included in this work. They were 42 (46.7%) males and 48 (53.3%) females, their
age ranged from 20-50 years in males, and 20-45 years in females with mean (44.4±2.4) years. Twenty apparently healthy person, age and sex matched to the patients were included as a control group. Comparison between the groups of SLE patients, RA patients and controls as regards titer of auto antibodies (LA, RO, SM, anti-DNA, ANA) showed statistically significant differences between SLE patients and both RA patients and controls (p<0.001). Vitamin D level was found to be lower than normal in all patients groups. It was lower in RA patients 7.62±1.58 than in SLE 12.81±1.92 and in Behcet's disease 13.68±1.99,
comparing vitamin D level in patients and controls showed that it was significantly lower in patients group than controls (p<0.001).Vitamin D level showed a significant negative correlation with various markers of disease activities of the studied groups, where p value was <0.001 with DAS28 in RA patients and with SLEDIA in SLE patients while it was 0.009 with BDCAF in Behcet's disease. Conclusion: The current study stressed the high prevalence of vitamin D deficiency in patients with autoimmune and inflammatory diseases including RA, SLE and Behcet's disease. Correlation between this defiecincy and indices of disease activity suggest the major role of vitamin D in modulation of immunological etiopathogenesis of these diseases.