Vitamin d from dietary intake or sun exposure requires two activation steps in the body. The first activation occurs in the liver, while the second activation occurs in the kidneys, allowing for regulation of calcium metabolism. However, vitamin d receptors are present throughout the body, in tissue such as the skin, cartilage, heart, prostate, bones and intestines. Thus, the second activation step also takes place in local tissues. Recent discoveries have highlighted the important modulatory effects of vitamin d on various cells of the immune system.vitamin d enhances and regulates immune function. It is known that various cells of the immune system, such as t lymphocytes and antigen presenting cells, express the vitamin d receptor on their surface when activated. Recently, it has been found that treatment of these immune cells with vitamin d influences their expression of cytokines, which are chemical messengers of the immune system. The immune modulating effects of vitamin d extend to monocytes and dendritic cells of the immune system as well. Dendritic cells are important antigen-processing cells of the immune system that function to initiate the immune response. Vitamin d may prevent overactivity of the immune response and keep the immune system in a normal healthy state of vigilance.vitamin d supports optimal cardiovascular function. Research has uncovered the role vitamin d plays in supporting cardiac function. Heart myocytes (cells) express the vitamin d receptor, as do smooth muscle cells of blood vessels. The benefits of vitamin d on the heart are potentially far-reaching. Studies on mice heart cells have shown that vitamin d administration impacts their growth and proliferation. In these cells, vitamin d inhibited the release of a protein that could be detrimental to the function of these cells, displaying cardioprotective properties. It has also been shown that vitamin d has a modulatory effect on heart rhythm.