If you are taking Prednisone you need supplemental vitamin D and calcium

Calcium and Vitamin D - There is a reduction in the body's ability to activate Vitamin D when taking corticosteroids, thus increasing the risk of bone loss as well as cataracts. The list of other possible benefits of Calcium and Vitamin D is extensive ranging from cancer prevention to heart disease to mental conditions. People taking corticosteroids on a long term basis (2 or more weeks) should ask their health care provider to be tested for vitamin D deficiency and to possibly be put on calcium and vitamin D supplements. Note: Calcium is an essential nutrient that is obtainable only from foods and supplements.