Vitamin D deficiency is implicated in several medical conditions and has several beneficial physiological effects. The adequate daily intake of vitamin D is between 2000-4000 IU. Nowadays, vitamin D deficiency became a phenomenon among people in Taif. Therefore, to what extent vitamin D deficiency is associated with epidemics and immune system efficiency. A total of 101 (59 males) and (42 females) were recruited in this study. Sera were extracted on the first day to estimate vitamin D3, immunoglobulins, cytokines, complement proteins, rheumatoid factor and C-reactive protein as a baseline. Participants were given 4000 IU/day of vitamin D3 orally for twenty days. On the twentieth day, sera were extracted for same parameters evaluation. After twenty days of supplementation serum vitamin D3 levels increased by approximately four folds in most subjects. This increment was accompanied with a significant IgM levels increase (31% in females) and (28% in males) in which P values <0.05 corresponding to baseline, and a slight increase in IgA, C4 and C3. Inversely, serum levels of IgG significantly decreased in female subjects in which p value was 0.05< corresponding to baseline. Moreover, both interleukine-7 and tumour necrosis factor-α levels decreased for about 50% in both female and male participants. In conclusion, twenty days of 4000 IU/day of oral vitamin D3 supplementation can change vitamin D status from deficient to normal levels in individuals that assumed to be healthy. Vitamin D improves both innate and adaptive immunity and can prevent autoimmune reaction, and might serve as anti-inflammatory agent.