Factors Affecting Calcium Absorption

Calcium (Ca) is absorbed in inorganic form. The absorption occurs mostly in the proximal parts of the small intestines. 150 to 200 mg Ca is absorbed per day. Many factors affect the absorption of Ca as given below:

1. Vitamin D: It greatly increases the absorption of Ca by increasing the amount of the specific transport protein responsible for active transport of Ca in the intestinal wall.
   
   
2. Parathyroid Hormone: It increases Ca absorption but the effect is less marked than that of vitamin D.
   
   
3. Ca:P ration in the food: For an optimum Ca absorption this ratio should be within the limits of 1:2 to 2:1. Excess of phosphates in the gastrointestinal tract decreases Ca absorption.
   
   
4. Presence of free Fatty acids: When fat absorption is impaired, then the unabsorbed fatty acids react with free Ca to form insoluble Ca soaps. Ca absorption is thus interfered with. For the same reason excessive intake of fats (free from vitamin D) decreases Ca absorption.
   
   
5. Presence of Anions: Oxalates, carbonates, sulfates and phosphates inhibit Ca absorption because Ca salts of these anions are insoluble. Excess of phytic acid which is abundantly found in unrefined cereal foods has the same effect. The Ca of soluble salts, e.g. chloride, gluconate and lactate is absorbed to a greater extent.
   
   
6. Proteins in diet: These facilitate Ca absorption because amino acid salts of Ca are more soluble in aqueous solution of amino acids.
   
   
7. Intestinal pH: If less (i.e. acidic), it favors Ca absorption because Ca salts are more soluble in an acid medium. Lactose facilitates Ca absorption by increasing acidity of the intestinal tract because some of it forms lactic acid.
   
   
8. Ca deficiency: If the body is deficient in Ca, its absorption is increased. This probably mediated through an increased parathyroid activity.
   
   
9. Intake of a Ca-deficient diet: If the diet has been deficient in Ca, then the absorption Ca increases. This is a type of body’s adaptation to a low Ca diet.