Each tablet contains calcium carbonate 1250 mg (equivalent to 500 mg of elemental calcium) & colecalciferol 400 IU (equivalent to 10 micrograms vitamin D3). Calcium is needed for the formation of strong bones & healthy teeth & is involved in helping the blood to clot. Vitamin D is needed for calcium to be absorbed from the gut, & deficiency can lead to low calcium levels & subsequent weakening of bones.