Absorption of calcium

Absorption of calcium
The amount of calcium in food items that we eat is absorbed differently. Like the calcium in spinach and calcium in milk is absorbed to the blood differently. The absorbability of calcium from spinach was compared with the absorbability of Ca from milk in healthy adults. Absorption was higher from milk in every case, with the mean absorption from milk averaging 27.6% and from spinach, 5.1%.

Thus, spinach Ca is much less readily available than milk Ca.

The presence of lactose (milk sugar), lactase (the enzyme that breaks down lactose), and the acidic amino acids, lysine and arginine, are all factors that improve calcium absorption.

Decreased absorption is associated with diets high in fiber. Foods such as whole grains and spinach are high in phytates and oxalates, compounds known to bind with calcium and reduce absorption.

Vitamin D intake is a second factor, as active calcium transport is directly and proportionally dependent on the presence in the intestinal cell of calbindin D9k, the biosynthesis of which is totally vitamin D dependent. 

Absorption in jejunum and ileum is the major absorptive process when calcium intake is adequate. No more than 10% of total calcium absorption takes place in the large intestine.

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