Calcium has a structural role in bones and teeth. Calcium is essential for the cellular structure, muscle contraction, nerve transmission, enzyme activation and hormone function. Bone density increases in the first 30 years of life, reaching its peak at about the age of 30. Afterwards bone density declines, and the decline increases more rapidly in women after menopause.Vitamin D is essential for promoting the absorption and utilisation of calcium and phosphorus and normal calcification of the skeleton.