Calcium absorption in intestine and its re-absorption in kidney involve similar processes that include both passive paracellular and active transcellular pathways.
Absorption of calcium involves an epithelial calcium channel, specifically transient receptor potential channel and the calcium-binding transport protein calbindin 9K, which binds calcium for transport into cell.
The complexity of the calcium absorbing system arises because the level of dietary calcium, and consequently of luminal calcium, can vary over very wide limits and also the level of a activity of the different mechanisms for calcium varies on passing from duodenum to jejunum and ileum.
Factors that improve calcium absorption include adequate amounts of protein, magnesium, phosphorous, and vitamin D.
Calcium is best absorbed in an acid environment. Therefore calcium is better absorbed when no consumed with antacids.
The absorption of calcium also depends on the presence of adequate amounts of vitamin D, which works with parathyroid hormones to regulate the amount of calcium in the blood.
Conditions that reduce calcium absorption include high or excessive intakes of oxalates and phytates, found in foods such as spinach and unleavened whole wheat products.
Stress also can reduce absorption of calcium.
Lack of exercise can reduce calcium absorption as well as cause an increase in calcium losses. These life habits can immobility lead to calcium deficiency. Calcium deficiency can increase risk of bone disorders such as osteoporosis.
Calcium is absorbed along the small intestine, more in the duodenum and proximal jejunum than the ileum. The absorption of calcium is completed within 4 hours after its oral intake.
Absorption process of calcium
