Calcium (Ca) forms about 1.5% of adult body weight. Normal serum or plasma Ca level is 9 to 11mg per 100 ml. The red blood cells contain very little Ca. More than 99% of Ca in the body occurs in bones as its phosphate and carbonate. The bone Ca is constantly exchanged with the Ca of interstitial fluid and this process is regulated by the parathyroid harmone.

   Plasma or Serum Calcium (Ca)

The Ca of Plasma or serum occurs in two forms:

  1. Non-diffusible: This fraction of serum Ca cannot be dialyzed out because it is in firm combination with plasma proteins especially albumin. Its level is 3.0 to 4.4 mg per 100 ml; it will be low in hypoproteinemia.
  2. Diffusible: This fraction can be dialyzed out. It consists of two sub-fractions which are given below:
    Ionized Ca: Its level is 5.45 to 6.23 mg per 100 ml. This is the physiologically active form of Ca. It is increased in hyperparathyroidism and decreased in hypoparathyroidism. Tetany occurs if the level of ionized Ca falls below 4.3 mg per 100 ml.
    Complexed Ca: Its level is less than 0.6 mg per 100 ml. It is in complex form with plasma anions such as citrate and phosphate.

   Dietary Sources of Ca

Milk (120 mg%) and milk products are the best dietary sources of Ca. Other good sources are egg yolk, beans, leafy vegetable and hard drinking water. In spite of their high Ca content some vegetable foods such as spinach contain also oxalates and benzoate and are a poor source of Ca because calcium oxalate and benzoate thus formed are insoluble and are not absorbed. Ca is also ingested as Ca(OH)2 on betel leaves.