Calcium is an essential mineral required by the human body. 99% of bodily calcium is present in the bones & teeth, where it plays a structural role. The major benefit of calcium relates to reducing the risk of developing osteoporosis. Absorption of calcium is affected by factors including age, diet, pregnancy and being post-menopausal. Vitamin D is required for calcium absorption, whilst vitamin K is essential for ensuring the absorbed calcium is used for the calcification of bone. Excessive intakes of calcium supplements may promote constipation.