Out of approximately 1200 gram of calcium present in the adult body, 99% is in the bones and teeth and remaining 1% is widely distributed in body fluids where it fulfils many functions.
- Calcium together with phosphorus and other elements give rigidity to bones and teeth. This characteristic makes it possible for the bones to support the body. Bone forms protective cavities for vital organs- the heart and lungs in the chest cavity, the brain in cranial cavity.
- Calcium acts as a catalyst for the conversion of prothrombin to thrombin, this being one of the several steps in the clotting of blood.
- It activates the permeability of the cell membrane (regulating the passage of substances into and out of cells).
- It activates the number of enzymes including lipase, adenosine triphosphate and some proteolytic enzymes.
- It has a role in the transmission of nerve impulses (conveying message from one nerve cell to another).
- It is directly related to muscle contraction. In the absence of calcium, muscles lose their ability to contract.
- It aids in the absorption of vitamin B12 from the ileum.
Milk and milk products are excellent sources of calcium. Certain green leafy vegetables such as mustard green, turnip greens, mint, spinach, carrot leaves rank next to dairy products in their calcium content. Citrus fruits, legumes, meats, grains and nuts provide the least calcium.
A deficiency of calcium in the diet results in retarded calcification of bones and teeth in the young. Due to the deficiency of calcium bones start bending and there is enlargement of ankle and wrist. In children, the deficiency disease is known as Rickets and in adults, as Osteomalacia. Repeated pregnancies coupled with inadequate dietary intake can also give rise to the deficiency of calcium.