Structural component of bones and teeth; role in intracellular and hormonal secretion regulation, muscle contraction, and activation of some enzyme systems.
Calcium is maintained relatively high concentration in the blood and extracellular fluids, where it is needed to facilitate such functions as blood coagulation and intercellular communications. Blood calcium levels are rigorously controlled so that if blood levels drop the body will rapidly respond by stimulating bone resorption, thereby releasing stored calcium into the blood.
Calcium also enables human blood to clot normally and regulates our muscle contractions, including heartbeat
The most well-known calcium function is to build and strengthen bones and teeth. The calcium in bones serves as a reservoir for calcium that is needed throughout the body. Calcium helps human bones to grow strong until the age of 20-25, when bone density reaches its peak. About 99% of the body’s calcium is stored in bones, and the remaining 1% is found in blood, muscle, and other tissues.
Calcium also is the key factor in normal transmission of nerve impulses. Calcium binds to vesicles that contain neurotransmitters, causing a release into the neural synapses (junction between nerve cells). This allows the flow of ions in and out of nerve cells. If calcium is lacking, nerve-cell function will fail.
Calcium is a key component of the cell membrane and controls cell permeability and electrical properties.
In order to perform daily functions, the body works to keep a steady amount of calcium in the blood and tissues. If calcium levels drop too low in the blood, parathyroid hormone (PTH) will signal the bones to release calcium into the bloodstream.
Deficiency symptoms
A low calcium intake during the growing years limits the bones’ ability to reach their optimal mass and density.
The symptoms of calcium deficiency include rickets, osteomalacia, osteoporosis, scurvy, tetany, parathyroid hyperplasia, stunted growth, laryngospasm.
Deficiency of calcium in young girls causes late puberty, irregular menstruation, excessive bleeding with crampy pain during this period, anemia and lowered state of body resistance against infection.
A more serious deficiency of calcium, called hypocalcemia, results from diseases such as kidney failure, surgeries of the digestive tract like gastric bypass, or medications like diuretics that interfere with absorption.
Food sources
Calcium is found in milk, milk products, sardines, clams, oysters, cheese and dairy foods, dark green vegetables (turnip greens, broccoli, legumes), dried fruits and nuts.
Calcium is classically associated with dairy products: milk, yoghurt and cheeses are rich sources of calcium, providing the major share of calcium from foods in the general diet in the United States and Canada.
When substantial amounts of grains are consumed, for like breads or as maize, these can be important sources, although the calcium in cereals tends to be less bioavailable than that in dairy products.
Function, deficiency and food sources of calcium
