Calcium and Phosphorus: Functions, Food sources, Absorption and utilisation

Calcium and Phosphorus: Functions, Food sources, Absorption and utilisation

Of all the minerals found in our body calcium and phosphorus are by far present in the largest amount. Together these two minerals account for 75 percent of the total mineral content of the body. The human body contains approximately 1200g of calcium, most of which is present in bones and teeth and the remaining in soft tissues and in the body fluids. On the other hand, only 400-700g of phosphorus is contained in the body. Like calcium most of it is also present in bones and teeth and the remaining in soft tissues and body fluids.


Calcium and phosphorus basically serve two important functions in the body one relating to the development of bones and teeth and the other to the regulation of body processes.

  • Development of bones and teeth: Calcium and phosphorus are mainly present in bones and teeth. The ratio of calcium and phosphorus in the bones is roughly 2:1. Calcium in the bone combines with phosphorus, some other minerals and water to form a compound. It is this compound which provides rigidity and firmness to the bones. Teeth, like the bones, also require calcium for their proper development. It is for this reason that the need for calcium is the most during the growing years.

  • Regulation of body processes: Apart from building bones and teeth, calcium and phosphorus perform regulatory functions as well.

  • Calcium Helps In:

    • Regulating the contraction and relaxatation of muscles especially that of the heart,

    • Regulating the passage of substances into and out of the cells,

    • Conveying messages from one nerve cell to another and

    • Clotting of blood.

  • Phosphorus, also performs several important functions.

It is required for the:

    • Formation of a substance which aids in transport of fat in the blood,

    • Synthesis of certain coenzymes which play a crucial role in metabolism,

    • Formation of certain basic, genetic material. This genetic material is involved in passing on of specific characteristics from to children and

    • Capture and storage of vital energy in the cells of many tissues by forming a high-energy compound. Muscle tissue is a prominent example where phosphorus helps in energy storage and thus fuels muscle contraction.

Food Sources of Calcium

Milk and milk products like curd, khoa, channa (cottage cheese) are excellent sources of calcium. Foods like fish (e.g. chingri, chela) especially dried fish and other sea foods (e.g. crab, shrimp) provide substantial quantities of calcium.

Among the plant sources, ragi (a millet grown in South India) is particularly rich in calcium. Pulses like bengal gram, black gram, green gram, moth beans, rajmah, soyabean contribute substantial amounts of calcium. Green leafy vegetables (like amaranth leaves, colocasia leaves, fenugreek leaves, mustard leaves) also contain good amounts. Among nuts and oilseeds, gingelly (til) seed is particularly rich in calcium. Others like coconut, almonds, walnuts have a fairly good amount of calcium.

Food Sources of Phosphorus

As for the sources of phosphorus, a diet that furnishes enough protein and calcium would normally provide sufficient phosphorus. Eggs, milk, poultry, fish are excellent sources of phosphorus. Cereals too are rich sources of this mineral.

Absorption and Utilization

Calcium is absorbed chiefly from the upper part of the intestine. Normally it is seen that from an average Indian diet only 20-30 per cent of calcium gets absorbed. The rest is excreted in the faeces. The absorbed calcium is then used to perform various functions as has been discussed earlier. Part of the absorbed calcium is also excreted in the urine but the amount is very small.

Only a small proportion of the calcium in the diet is absorbed. What are the reasons for this? You will find the answer as you read about the factors influencing calcium absorption. Let us now study these factors and try to understand how they influence calcium absorption.

The factors include:

  • Body need: The efficiency of absorption of calcium increases during periods  of rapid growth i.e. infancy, childhood, pregnancy, lactation. When the body's demand for calcium increases the absorption of calcium also increases to meet this increased demand.

  • Nutrients in the diet: Certain nutrients like Vitamin D, Protein and Carbohydrate present in the diet help to improve absorption of calcium.

Another nutrient that influences calcium absorption is phosphorus. In fact, the proportion of calcium and phosphorus in the diet affects calcium absorption. Excess phosphorus tends to lower calcium absorption.

  • Inhibitors: Inhibitors are substances present in food which hinder calcium absorption. You have learnt earlier that cereals and green leafy vegetables are rich in calcium. But all the calcium present in these foods is not available to the body. This is because these food items have some substances (such as phytates 'in cereals and oxalates in green leafy vegetables) present in them which bind calcium and inhibit its absorption.

So far you have read about absorption and excretion of calcium. Let us now study about absorption and excretion of phosphorus. As in the case of calcium, absorption of phosphorus also takes place from the upper part of the small intestine. However, a considerable amount of phosphorus in cereals, pulses and nuts exists in a bound form which is not absorbed. The body takes in only the free form. The absorbed phosphorus then gets used in the body and performs
various functions.

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