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Chapter: Biochemistry: Minerals


About 99% of the body calcium is found in the bones and teeth where it is combined with phosphorus and other elements to give rigidity to the bone.



·           About 99% of the body calcium is found in the bones and teeth where it is combined with phosphorus and other elements to give rigidity to the bone.

·           The bones also serve as the store house for calcium which is needed for a number of cellular functions.

·           Calcium is required for the complex process of blood coagulation.

·           Together with other elements it regulates the passage of ions into and out of cells.

·           It controls the transmission of nerve impulses, brings about the normal contraction of muscles, including the heart.

·           It also activate certain enzymes like adenosine triphosphatases, succinate dehydrogenase etc.

Distribution of calcium

Calcium is distributed in the body as follows:

Serum - 9-11 mg/100 ml

C.S.F - 4.5-5 mg/100 ml

Muscle - 70 mg/100 gm

Nerve - 15 mg / 100 gm

Calcium content of blood

The calcium content of plasma is fairly constant ranging from 9-11 mg/100 ml. This level is maintained constant in healthy individuals by the following factors: (i) the amount of calcium absorbed from food through the intestine and (ii) the secretion of parathyroid hormone which controls the level of calcium in blood.


Milk and cheese are rich sources of calcium. Egg yolk, cabbage, beans and cauliflower are good sources.


Growing children require more amount of calcium, because of the increased rate of growth.

Infants - 0.36-0.54 g/day

Children - 0.8-1.2 g/day.

Adults - 0.8 g/day.

During pregnancy and lactation - 1.5 g/day

Absorption and excretion

Calcium is taken in the diet as calcium salts of phosphate, carbonate, tartrate and oxalate. Calcium is actively absorbed in the upper small intestine. Calcium is excreted in the urine, bile and digestive secretions.

Factors affecting calcium absorption

Some of the factors which influence the absorption of the calcium in the intestine are:

Vitamin D

Vitamin D promotes absorption of calcium.


High level of proteins in the diet helps to increase the absorption of calcium.


Acidic environment in intestine favours calcium absorption.


Lactose in chief increase the absorption of calcium. The beneficial effect of lactose is due to increased acidity (lactic acid) of the intestinal content which leads to increased calcium absorption.


Excess of phosphate in diet lowers the calcium absorption. The ratio of calcium and phosphorus in the diet should be 1:1.

Fats and fatty acids

Faulty absorption of fats leads to the presence of large amounts of fatty acids in the intestine were interferes with calcium absorption, as fatty acids form insoluble salt with calcium which are excreted in the feces.

Oxalic acid

Oxalic acid present in certain food forms insoluble calcium oxalate which is excreted in the feces and interfere with the calcium absorption.

Calcium balance

Dietary calcium which is not absorbed in the intestine is excreted in the feces. A small part of the absorbed calcium is excreted in urine. The calcium balance i.e. the difference between the quantity of calcium ingested and that excreted in urine and feces.


Calcium deficiency becomes evident only after a long period of inadequate intake. A dietary deficiency does not lower the blood calcium since the bones will supply the amount required. Rickets (in children) is a disease more directly related to vitamin D deficiency, but calcium and phophorus metabolism are also involved. Tetany and osteomalacia (in adults) are the diseases result from the deficiency of calcium.


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