Calcium (Ca) is a mineral that makes up the main part of the structure of bones. Two percent (2%) of the weight of the body is due to calcium, with half in the bones and half in solution in the blood and other bodily fluids. The level of calcium in the bones and blood is controlled by two hormones, parathormone (which raises blood calcium) and calcitonin (which lowers blood calcium), that are produced in the parathyroid glands in the neck. It is essential for the production of many enzymes, in muscle contraction, and electrical conduction in nerves, as well as bone structure.
The absorption of calcium from the gut is dependent on vitamin D, which is obtained by sun irradiation of cholesterol in the skin. It is found mainly in dairy products (eg: cheese, milk, yoghurt), bony fish (eg: sardines, salmon); and to a lesser extent in peas, beans, broccoli, almonds and whole grain cereals. Calcium in various forms is found in numerous nutritional supplements and antacids. Taking vitamin D supplements with calcium improves the uptake of the calcium into the body.
Calcium supplements are safe in pregnancy, breastfeeding and children, but must be used with caution in patients with kidney stones, kidney disease and diabetes. Do not take these supplements if you suffering from severe kidney disease or hypercalcaemia (high blood calcium). The side effects of calcium supplements may include constipation, hot flushes, sweating, low blood pressure and rarely kidney stones (severe loin pain). Interactions are possible with iron, digoxin, tetracycline, fluoride and calcium channel blockers.
The recommended daily dietary intake is 300 mg. in infants, 800 mg. in children, 800 mg. in adults and 1000 mg. in the elderly.