Compare Active Ingredients OS•CAL® Extra D3† Calcium Supplement Support for Bone Health Easy to Swallow 500 mg Calcium 600 IU Vitamin D3 Laboratory Tested Guaranteed Quality Calcium is an important mineral for supporting bone health. Calcium aslo works to support muscle and nerve function. Vitamin D3 is added to assist with Calcium absorption and as support for immune function. Adequate Calcium and Vitamin D3 as part of a healthful diet, along with physical activity, may reduce the risk of osteoporosis in later life.