Calcium is a mineral that helps build strong bones and teeth and regulates muscle contraction. Milk and dairy products have long been held as an important source of calcium. In addition to calcium, Vitamin D is important because it helps the body absorb and retain calcium in the bones, making them strong. Similarly, sufficient exercise is now seen as another vital factor in maintaining healthy bone structure and density. Concerns have been voiced that a lack of exercise in growing children will have a detrimental effect on their bones. Calcium can continue strengthening your bones until the age of 20 to 25 when peak bone mass is reached. After this point, your bones can only maintain or lose their density and grow weaker as a natural part of the ageing process. Inadequate dietary calcium intake before this age can increase the risk of brittle bone disease, as calcium is drawn from the bones as a reserve.