Calcium plays an important role in several body functions, including muscle contractions, enzyme function, and nerve conduction. Calcium is stored in the bones. Calcium levels in the blood are regulated by two hormones (parathyroid hormone and calcitonin) produced by the four parathyroid glands, located adjacent to the thyroid gland in the neck. These hormones include the following: High calcium in the blood may cause constipation, bone pain, kidney stones, or psychiatric diseases (including depression and confusion). This can be due to several reasons, the commonest being overproduction of parathyroid hormone or some form of cancer. Low calcium in the blood leads to pins and needle sensation over the extremities of hands and feet, muscle cramps and is usually due to low levels of parathyroid hormone. Other metabolic disorders are osteoporosis (brittle bones which may cause fractures, particularly in women after menopause), and Paget’s disease, which is associated with enlarged and deformed bones in older individuals.