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Calcium absorption in humans is regulated by a biological control system that depends on the following: a balance between calcium made available from bone resorption, intestinal absorption, and kidney reabsorption. When calcium intake is high, passive absorption occurs through the middle section of the small intestine. A small amount of calcium absorption takes place in the large intestine by both active and passive processes.
Milk and dairy products are the major source of calcium for most people. Other good sources are broccoli, dark green leafy vegetables, legumes, nuts, and whole grains.
Calcium is the most abundant mineral found with in the human body. It is widely known for its important role in the development of bones and teeth in children and teenagers, but it is very important to men and woman of all ages. An average healthy male contains about 2.5 to 3 pounds of calcium while a female contain about 2 pounds. Approximately 99 percent of calcium is present in the bones and teeth, which leaves one percent in cells and body fluids. Although only a small amount of calcium is in the blood, the body goes to great lengths to maintain blood-calcium levels. Three regulatory mechanisms control blood-calcium. If levels drop too low, intestinal calcium absorption can increase, calcium can be released from bones, and/or the kidneys reduce calcium excretion.
Toxicities & Precautions
Large doses of calcium are efficiently excreted by the body and do not usually produce toxic effects unless the individual has a history of kidney stones.
Functions in the Body
Involved in multiple steps of the blood clotting process.
Bones and Teeth
Most important function is in the development and maintenance of healthy bones and teeth. Greatest need for calcium is during childhood, pregnancy, and lactation.
Activates multiple enzyme systems responsible for fat digestion, muscle contraction, and protein metabolism.
Helps to initiate muscle contractions. Calcium plays a vital role in the contraction-relaxation cycle that regulates a normal heartbeat.
Plays a role in the regulation and transmission of nerve impulses.
Symptoms & Causes of Deficiency
The following are skeletal diseases associated with calcium deficiency. Rickets is the classical calcium deficiency disease. It occurs in children and causes a variety of bone deformities. When this condition develops in adults, it is called osteomalacia (ŏs'tē-ō-mə-lā'shə, -shē-ə). Osteoporosis is associated with a lack of vitamin D, which causes a reduction in the absorption of calcium. The symptoms of calcium deficiency include back and leg pains, brittle or soft bones, heart palpitations, high blood pressure, insomnia, muscle cramps, nervous disorders, and tooth decay. Osteoporosis and osteomalacia are the two main adult conditions caused by calcium deficiency. Bone deformities and fractures are the result. Magnesium deficiency causes various abnormalities in calcium metabolism. Ingestion of foods high in phosphorus (animal protein and soft drinks) advances the urinary loss of calcium. Intestinal inflammatory conditions can decrease calcium absorption. Other significant factors that can negatively influence calcium levels include caffeine, excess dietary fat and fiber, and lack of exercise.