Vitamin D3 plays an important role in the maintenance of several organ systems and its deficiency causes multiple and complex dysfunctions for the organism. Vitamin D3 has been originally described to regulate calcemia by absorbing calcium in the intestine and by increasing re-absorption of calcium in the kidneys. Recent studies have shown the important effects of Vitamin D3 on many other systems, especially as a modulator of the immune system, and its deficiency has been linked to several autoimmune and inflammatory diseases such as multiple sclerosis, inflammatory bowel disease, lupus erythematosus, rheumatoid arthritis and asthma.