About this item 00 mg of Calcium, 800 IU of Vitamin D3, Plus Magnesium & Zinc Doctor recommended Caltrate is the No 1 selling brand of calcium supplements. Among the top most clinically studied calcium brands in the world One tablet contains 6 mg of Calcium, 8 IU of Vitamin D3 and Magnesium for bone health. Includes Zinc and other minerals to help support collagen production for stronger, more resilient bones.