Calcium and phosphorus are some of the nutrients most key to bodily function. In mineral form, they help compose bone, and they play major roles in metabolic activity. Hormones tightly regulate their levels in the body -- partly a choreography of maintaining a balance between the two.
Nutrients
Calcium ranks as the most common of the body’s minerals, while phosphorus is the next most abundant. Most of these nutrients -- 99 percent of calcium and 85 percent of phosphorus -- is in the bones and teeth of the skeleton. The rest is bound up in fluids, blood and tissues. In addition to their structural contribution to bone, both calcium and phosphorus are critical for metabolic function. Dietary sources of phosphorus include foods rich in protein, such as milk, eggs and meat; calcium is similarly available in a range of foods, particularly dairy products.
In the Skeleton
In combination as calcium-phosphate crystals, calcium and phosphorus constitute the main mineralized component of the skeleton. Chief among these crystal structures are hydroxyapatites. Calcium-phosphate makes bones hard and strong, while cartilaginous fibers of collagen ensure a suppleness that otherwise would result in a brittle skeleton that easily shattered. As a person develops from embryo to maturity, a skeleton dominated by cartilage gradually hardens as more mineral substance develops.
Regulation
Calcium and phosphorus cycle between different parts of the body as needed -- a dance from bone to fluid and tissue and back again that is regulated by hormones. A decrease in blood-calcium concentrations -- registered by the parathyroid glands -- provokes a release of parathyroid hormone, which then changes vitamin D in the kidneys into calcitriol. This in turn enhances calcium absorption in the small intestine, where dietary calcium and phosphorus are taken in by the body; collaborating with parathyroid hormone, this stimulates special cells called osteoclasts that transfer calcium and phosphorus from the skeletal reservoir into the body. Parathyroid hormone also suppresses the release of calcium and increases the release of phosphorus in the urine.
Interactions
Scientists continue to research the connection between phosphorus and calcium levels in the blood. Diets overly rich in phosphorus and deficient in calcium – as when soft drinks are consumed at the expense of milk – may disrupt the nutrient balance, as excess phosphorus tends to suppress the transformation of vitamin D into calcitriol, one of the routes by which the body maintains calcium levels. This is one reason why the normal regulatory actions set in effect by parathyroid hormone to combat lowered calcium concentration involve upping the urinary loss of phosphorus.
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