Calcium

Calcium is an element found in the periodic table and has an atomic number of 20. It is also the most abundant mineral found in the human body; 99 percent of total body calcium is stored in the bones and teeth. Calcium is one of the most essential minerals—it is needed not only for maintaining bone health, but also for proper muscle and nerve function. Calcium is necessary for blood vessel contraction and growth, the release of hormones and enzymes, and the maintenance of the body's basic structure.

Bones are constantly reconstructed and remodeled throughout an individual's lifetime. After bone has been broken down, calcium is then restored back into it in order to increase the strength of the bones. This cycle also occurs in an individual's growing years, when bone formation occurs more frequently than bone breakdown. As an individual ages, the balance between these two phases of bone growth changes. In aging adults, especially postmenopausal women, breakdown exceeds formation, leading to bone loss.

When the body's blood levels of calcium decrease, calcium that was stored in bones is used to replenish the body's calcium. Insufficient calcium intake, a decrease in calcium uptake, or an increased loss of calcium in urine can decrease total calcium in the body, leading to osteoporosis (also known as poor bones). Osteoporosis, which strikes about 10 million Americans, is the weakening of bones caused by an imbalance of bone destruction and building. In order to provide a strong foundation for bone, calcium intake needs to be increased and maximum bone stores must be made before age 30.

Hypocalcemia is a medical condition that usually occurs not from a decrease in uptake of calcium but as a side effect of other diseases, such as kidney failure or stomach problems. Both of these organ systems are crucial to calcium absorption in the body. Diuretics, medications that cause an individual to increase urinary excretion and are taken to decrease blood pressure, can also result in a decrease in calcium. Severe cases of hypocalcemia can result in irregular heart rates and death.

The Institute of Medicine and the National Academy of Sciences are both responsible for setting a standard recommended level of calcium, also known as the Dietary Reference Intake. For calcium, the recommended intake is listed as an Adequate Intake (AI), which is a suggested average intake level based on observed or experimentally determined levels. Research has shown that adults are not meeting these calcium requirements.

There are many calcium-rich foods suggested to prevent calcium deficiency, the top three being milk, yogurt, and cheese. According to the U.S. Department of Agriculture's Food Guide Pyramid, individuals age 2 and above need two to three servings of dairy products per day. A diet rich in protein, especially from animal sources, can cause calcium loss in the body. Sulfur, [Page 332]which is found in meat, increases calcium excretion, and a diet rich in meat causes bone demineralization.

Calcium is also responsible for muscle contraction and enzyme function. Calcium levels in the blood are regulated by the parathyroid hormone and calcitonin, a hormone that lowers the calcium in blood by slowing bone breakdown. When blood calcium levels fall, more parathyroid hormone is made by the parathyroid glands; less hormone is made if blood calcium levels are high. The hormone is what stimulates the digestive tract to absorb more calcium and causes kidneys to activate vitamin D, which causes even more absorption of calcium.

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