calcium

What is it?

Calcium, the most abundant mineral in the body, makes up about 1.5% to 2% of the body weight and 39% of the total body minerals. 

Approximately 99% of the calcium exists in the bones and teeth. The remaining 1% of calcium is in the blood and extracellular fluids and within cells of tissues, where it regulates many important metabolic functions, which are essential for life and health.

Functions - what does it do?

Bones and teeth. Calcium is used for building bones and teeth and in maintaining bone strength. Adequate calcium is necessary in the diet to allow for optimal gains in bone mass and density, before puberty and during adolescence. This period is when girls retain the greatest amount of calcium, which is especially important, as they should develop bones that would provide additional protection against osteoporosis in later years after menopause.  

Postmenopausal women need to obtain sufficient amounts of calcium to maintain bone health and to suppress PTH (parathyroid hormone). PTH causes the calcium from bones to be resorbed into the blood when blood calcium levels are low.  

Increased calcium intakes are recommended during pregnancy and lactation to meet increased needs.  

Other functions

Calcium is also required for: -

• muscle contraction (e.g. regulation of the heart muscle contractions)

• nerve transmission, blood clotting, and maintenance of cell membranes.

Requirements - How much do we need?

Sources - Where is it found?

Supplementation

Calcium supplementation can be used when dietary intake is insufficient. Since there are several different types of calcium supplements available, which contain differing amounts of elemental calcium, one should discuss the choice of such supplements with the doctor.

Example: A calcium carbonate supplement contains only 40% of its weight in elemental calcium; therefore, if 500 mg of elemental calcium is required then at least 1250 mg of calcium carbonate needs to be taken, i.e. 40% of 1250 mg = 500 mg.

Calcium carbonate, commonly found in calcium-based antacid tablets, is the most common supplement used.

Deficiency - When you have too little

The bones are in a constant state of remodelling, with calcium being resorbed into the blood and new bone being formed constantly, with about 4% of surfaces involved at any given time. The calcium in your diet spares and maintains the calcium in your bones. However during periods of inadequate calcium intake your bones release calcium into the blood to balance the shortage and make calcium available for the body’s functions. Continued inadequate calcium intake, together with other nutrients could lead to osteoporosis.

What is osteoporosis?

Osteoporosis (from the Greek "porous bones") is a decrease in bone mass and strength to the point that the skeleton is unable to sustain ordinary stresses causing it to fracture more easily. The bones can become so brittle that the slightest knock can cause a fracture or break in the bone, usually the hip, spine or wrist. Osteoporosis is the major cause of bone fractures in older people, especially postmenopausal women.

The cause

During the mid-30’s everyone begins to lose very small amounts of bone and there is a normal decline in bone production and therefore bone density. This happens because more bone is being removed than replaced. Bone loss accelerates at menopause, with some women losing up to 30% of bone mass in the first five years after the menopause.

What role does calcium play?

The best treatment for osteoporosis is prevention. Calcium in an essential nutrient and together with phosphorous, vitamin D, and other nutrients, is needed in adequate amounts to develop healthy bones. Large amounts of calcium are needed for the development of the skeleton and therefore it is essential that adequate amounts of calcium be provided in the diet at all ages, but especially before puberty and through adolescence, to develop peak bone mass. The intake of adequate amounts of calcium and vitamin D for healthy bones is also essential throughout adulthood. Weight-bearing exercise during adolescence into adulthood also plays a role in increasing peak bone mass, which can lower the risk of fractures in later years.  

Tetany

A faulty calcium metabolism can cause the blood calcium level to fall below a critical point causing an abnormal body condition called tetany. During tetany, the muscle contracts sharply and fails to relax thus causing the body to stiffen. It sometimes occurs during pregnancy in women who have consumed too little calcium or too much phosphorous, which causes a decrease in calcium absorption. Newborn infants fed undiluted cow’s milk may also experience tetany because of its high phosphorous content compared to calcium.

Toxicity - When you have too much

A very high intake of calcium especially in the presence of high blood levels of vitamin D, is a potential cause of hypercalcaemia (i.e. an abnormally high concentration of calcium in the blood). This may lead to excessive calcification (i.e. hardening caused by the deposition of calcium salts) in the bone and soft tissue.