Calcium

Calcium is a chemical element and member of the alkaline-earth metals group. In its pure form, calcium is a silvery-white substance. Calcium is one of the most abundant substances on Earth, making up about 3.64 percent of the Earth's crust. It is also the fifth most abundant element in the human body. Calcium is necessary for good health. It is essential to muscle contraction and is needed for the transmission of nerve impulses, the clotting (thickening) of blood, and to maintain healthy membranes (thin layers covering cells and organs through which materials, usually liquids and gases, can pass).

Calcium also helps regulate contractions of the most important muscle in the body, the heart. This was discovered in 1882, when British physician Sydney Ringer (1835-1910) showed that a heart would continue to beat in a solution of salt, calcium, and other chemicals. Large amounts of calcium are needed for a developing baby during pregnancy and for the production of mothers' milk. Most of the calcium in the body—about 99 percent—is contained in the bones and teeth. The remaining one percent circulates in the bloodstream where, as American biochemist Elmer McCollum proved in the early 1900s, it is essential for muscle contractions. Bones get their strength and rigidity from calcium, which makes up 70 percent of their weight.

Calcium was not known as an element until the early 1800s, when chemists trying to prove the existence of unknown metals in natural compounds began using the newly discovered phenomenon of electricity to break them apart. English chemist Sir Humphry Davy, a pioneer in the field of electrochemistry, first isolated elemental calcium in 1808 by electrolyzing a mixture of lime and mercuric oxide.

Natural calcium compounds are found most frequently in rocks and minerals. Calcium carbonate is the most abundant of these, making up over 40 percent of the content of limestone. (In fact, calcium's name comes from the Latin word "calx," or limestone). Marble, dolomite, seashells, pearls, and coral also contain large amounts of calcium carbonate. Today, the compound is used in toothpastes and antacid medicines, and is also an ingredient in white paint.

Calcium Carbide

Another important compound of calcium is carbide, which was discovered by German chemist Friedrich Wohler. In 1892 American scientist T. L. Willson produced calcium carbide by combining lime with carbon and heating the mixture. The result was a hard, brittle crystal that, when exposed to water, yielded calcium hydroxide and acetylene, a flammable gas used in welding. Calcium acetate is used in the production of plastics, and calcium hypochlorite is a bleaching agent and disinfectant.

When it is deficient (lacking) in the diet, calcium is released from the bones to maintain the level needed by the rest of the body. Over time, too little calcium can cause osteoporosis, a progressive weakening of the bones. Another bone disease called rickets can occur if the body does not have enough vitamin D to aid in calcium absorption. Rickets has plagued mankind for a long time. Archaeologists have found the bones of humans dating to about 50,000 B.C. that showed evidence of rickets.

Calcium is found in most plants and animals and is necessary for their health. Calcium phosphate is often used a fertilizer to enrich calcium-poor soil. Good sources of calcium in foods are tofu, milk and other dairy products, leafy green vegetables, sesame seeds, seaweeds, beans, almonds, and canned fish that contain the bones, such as sardines and salmon.