Calcium is a major mineral element of the body. It constitutes 1.5-2% of the body weight of an adult human. An average adult body contains about 1200gram of calcium of which over 98% is found in the bones. The level of calcium in the blood is usually about 10mg/dl. The developing fetus requires about 30 gram of calcium. There is a dynamic equilibrium between the calcium in the blood and in the skeleton and this interaction is maintained by the interaction of vitamin D, parathyroid hormone, and calcitonin.
Calcium is readily available from many sources.
- Animal Sources: The most important and the natural sources are milk and milk products e.g. cheese, curd, skimmed milk and buttermilk, eggs, and fish. A liter of cows milk provide 1100mg of calcium and human milk about 300 mg. Calcium occurs in milk as calcium caseinogenate which is readily assimilated by the body. It is also present in egg yolk.
- Plant Sources: it is also obtained from green leafy vegetables such as spinach, amaranth and the limiting factor in the complete absorption of calcium is the oxalic acid. It is present in cereals and the millet especially ragi. Some fruits contain a good amount of calcium such as Stiaphal.
An additional source of calcium is drinking water which may provide 200 mg of calcium per day.
Ionized calcium in the plasma has many vital functions. These areas follow:
- It is helpful in the formation of bones and teeth. Sufficient supply of calcium must be ensured in early life to build up the skeletal reserves. If this is not done, then there occurs an increased incidence of osteoporosis in old age.
- It is needed in coagulation or clotting of blood.
- By causing regulation of the membrane permeability, calcium ions control the excitability of the nerves. If plasma ionized calcium level falls markedly, tetany results in which spasm of various muscles groups occurs.
- Calcium ions act as a cofactor or activators of various enzymes in our body. A protein known as calmodulin is present within cells which can bind calcium. The calmodulin-calcium complex becomes attached to certain enzymes which are activated. This mechanism is important for the release of acetylcholine at the neuromuscular junctions.
- It takes part in the contraction of muscle including heart muscles and is also involved in the excitation and contraction coupling mechanism. These calcium ions can potentiate the effects of cardiac glycosides and therefore should not be given to patients who are using these drugs.
- Calcium ions are responsible for initiating contraction in the vascular and other smooth muscles. Calcium ions enter through specific channels just as is the case with cardiac muscles.
- It is essential for maintaining the integrity of the capillary wall.
- Calcium ions are also involved in the exocytosis process and thus have an important role in stimulus-secretion coupling in most exocrine and endocrine glands.
- Some hormones exert their effects through Calcium.
- It exerts profound effects on excitable tissues.
In young age, its deficient supply may lead to rickets in children and in adults it may lead to osteomalacia. Low levels also cause an increase in contraction of muscles. But otherwise, no clear-cut disease due to calcium deficiency has ever been observed, even under the condition of low intake.
Increase levels may affect the heart and lead to heart stops in systole and decrease conduction of cardiac impulses occur and thus can produce a heart attack. It may lead to weakness, fatigue and constipation and depression of central nervous system. But again overall its use is safe.