Calcium is essential to the human body. It is required for normal nerve, cell, muscle, and bone function. Vitamin D aids in the absorption of calcium and phosphorus by the body. Getting enough vitamin D, calcium, and phosphorus is essential for building and maintaining strong bones. This combination medication is used to prevent or treat low blood calcium levels in people who do not consume enough calcium. It may be used to treat bone loss (osteoporosis), weak bones (osteomalacia), and a certain muscle disease caused by low calcium levels. It may also be used in certain patients to make sure they are getting enough calcium (including women who are pregnant, nursing, or postmenopausal, people taking certain medications.