Calcium Deficiency
When calcium absorption is chronically low, because of low intakes, poor bioavailability, or conditions that impair intestinal absorption, there is a decrease in the serum ionized calcium concentration.
This in turn stimulates the release of PTH, which returns serum calcium to normal by increasing renal calcium reabsorption, stimulating the renal production of 1,25(OH)2D3, and inducing bone reabsorption.
The result of long-term calcium deficiency is accelerated bone loss in older individuals or the inability to fully achieve peak bone mass in younger individuals.
Dietary sources
The majority of dietary calcium in industrialized countries comes from milk products; one serving (i.e., 250 ml milk or yogurt or 40 g cheese) contains approximately 7.5 mmol (300 mg).
Nondairy sources (fruits, vegetables, and grain products) supply approximately 25% of total calcium. When substantial amounts of grains are consumed, for example, in breads or as maize products, these can be important sources, although the calcium in cereals tends to be less bioavailable than that in dairy products.
Other foods high in calcium include tofu set with a calcium salt, kale (cabbage), broccoli, and, increasingly, calcium-fortified juices and cereals.
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