Calcium Health Article

Calcium

Calcium is one of the most important elements in the diet because it is a structural component of bones, teeth, and soft tissues and is essential in many of the body's metabolic processes. It accounts for 1 to 2 percent of adult body weight, 99 percent of which is stored in bones and teeth. On the cellular level, calcium is used to regulate the permeability and electrical properties of biological membranes (such as cell walls), which in turn control muscle and nerve functions, glandular secretions, and blood vessel dilation and contraction. Calcium is also essential for proper blood clotting.

Because of its biological importance, calcium levels are carefully controlled in various compartments of the body. The three major regulators of blood calcium are parathyroid hormone (PTH), vitamin D, and calcitonin. PTH is normally released by the four parathyroid glands in the neck in response to low calcium levels in the bloodstream (hypocalcemia). PTH acts in three main ways: (1) It causes the gastrointestinal tract to increase calcium absorption from food, (2) it causes the bones to release some of their calcium stores, and (3) it causes the kidneys to excrete more phosphorous, which indirectly raises calcium levels.

Vitamin D works together with PTH on the bone and kidney and is necessary for intestinal absorption of calcium. Vitamin D can either be obtained from the diet or produced in the skin when it is exposed to sunlight. Insufficient vitamin D from these sources can result in rickets in children and osteomalacia in adults, conditions that result in bone deformities. Calcitonin, a hormone released by the thyroid, parathyroid, and thymus glands, lowers blood levels by promoting the deposition of calcium into bone.

Most dietary calcium is absorbed in the small intestine and transported in the bloodstream bound to albumin, a simple protein. Because of this method of transport, levels of albumin can also influence blood calcium measurements. Calcium is deposited in bone with phosphorous in a crystalline form of calcium phosphate.