Vitamin D is extremely important in helping maintain the balance of calcium in our bodies. In fact, that's all that vitamin D does! Vitamin D has a direct effect on the intestines and encourages the intestines to absorb calcium from the food that you have eaten (this is why most milks are fortified with vitamin D). Vitamin D also has an effect on the kidneys and tells the kidneys to not let any calcium escape into the urine. Therefore, it is possible for a person to take too much vitamin D so that they absorb too much calcium from their diet and hold on to too much calcium in their kidneys... and their calcium goes high.
Prednisone is a commonly prescribed corticosteroid (steroid, for short). These drugs have also been called "glucocorticoids" because of their effects on glucose metabolism: Increases in blood glucose are common among people taking prednisone and other steroids. Prednisone is a synthetic steroid that is used to treat a wide variety of inflammatory conditions, such as bursitis and arthritis in the joints. It's also prescribed for its immunosuppressive properties: for allergic reactions, acute flare-ups of asthma, autoimmune conditions, anti-rejection treatment after transplant surgery, and cancer chemotherapy, among many other uses.