Thus the plasma and interstitial fluids have a normal calcium ion concentration of about 1.2 mmol/litre. This ionic calcium is the calcium form that is important for the effect of calcium on the heart, the nervous system and bone formation.
Calcium is readily available from many sources. By far the best natural sources are milk and milk products e.g. cheese, curd, eggs and fish.
A liter of cow’s milk provides about 1200 mg of calcium and human milk about 300-mg. calcium occurs in milk as calcium caseinogenate, which is readily assimilated by the body.
The cheapest dietary sources are green leafy vegetables, cereals and millets. The limiting factor in the complete absorption of calcium from green leafy vegetables is the presence of oxalic acid with which calcium forms an insoluble compound; calcium oxalate, which interferes with the absorption of calcium Ragi, is a rich source of calcium. Rice is very deficient in calcium. The bioavailability of calcium from cereals is poor because of the presence of phytic acid, which forms an insoluble compound with calcium, calcium phytate.
Other sources of calcium are peas, beans, soybeans, lentils, and potatoes.
An additional source of calcium is drinking water, which may provide up to 200 mg/day. Some fruits e.g. Sitaphal contain good amount of calcium.
In other words, any well balanced diet usually has sufficient calcium to meet our needs. People who are well supplied with calcium during their childhood years not only live longer but also are less likely to develop some of the more serious disease of later life.
However, calcium cannot be absorbed unless we have an adequate supply of vitamin D in the diet.
Benefits of calcium
Ionized calcium in the plasma has many important functions including formation of bones and teeth, coagulation of blood, contraction of muscles, cardiac action, milk production, relay of electrical and chemical messages that arrive at a cell’s membrane to the biochemical machinery within the cell, keeping the membranes of the cell intact and in the metabolism of enzymes and hormones.
It also plays a crucial role in the transformation of light to electrical impulses in the retina.
In the bones, two minerals, calcium and phosphorus, are combined to give strength and firmness to the skeleton or bony structure of the body. Many chemical reactions of the body require both calcium and phosphorus. Hence there is a constant interchange of these minerals between the bones and the blood stream.
Young mothers need extra calcium, particularly during pregnancy and the nursing period.
Calcium is important for children and young people whose bones are growing rapidly.
It acts best with
In the body there is a close chemical relationship between calcium, phosphorus and vitamin D. a deficiency of any of these may produce a serious disturbance in the framework of the body. In children this disease is known as rickets. In adults it is called as osteomalacia.
Overall, about 20-30 percent of dietary calcium is normally absorbed. Absorption of calcium is increased by vitamin D and decreased by the presence of phytates, oxalates and fatty acids in the diet. Calcium absorption is regulated to some extent by the body’s need
No clear-cut disease due to calcium deficiency has ever been observed even under conditions of low intake. It has been established that if the intake of vitamin D is adequate, the problems of rickets and osteomalacia do not arise even with low calcium intake.
When the calcium level in the body drops below a safe level, the nerves become extremely irritable and the muscles go into spasms.
Crampy pains may be felt in various parts of the body, particularly in the larger muscles of the legs.
When the calcium is reduced in the blood stream, the heart quickly loses its power, becomes irregular, and may even stop beating altogether.
Infants with rickets are restless at night and tend to sleep poorly. The constant movement of the head on the pillow may wear off the hair. If this disease continues, the child’s normal development is retarded. He suffers from marked weakness in the bones, and there is considerable delay in his sitting up, crawling and walking.
The weight of his body may bend the bones and joints out of shape, causing such deformities as bowlegs, pigeon breast, and knock-knees.
Deficiency of calcium also results in a disease known as tetany. It also causes seizures because of its action of increasing excitability in the brain.
A daily intake of 400 to 500 mg of calcium has been suggested for adults.
The physiological requirements are higher in children, expectant and nursing mothers.
Effects of excessive intake of calcium
When the level of calcium in the body fluids rises above normal, the nervous system is depressed, and reflex activities of the central nervous system can become sluggish. Also increased calcium ion concentration decreases the QT interval of the heart and causes constipation and lack of appetite, probably because of the depressed contractility of the muscle walls of the gastrointestinal tract.