Calcium Requirement

Calcium is the most abundant mineral in the human body.  Of the body's total calcium, about 99% is in the bones and teeth where it plays a structural role.  The remaining 1% is present in body tissues and fluids where it is essential for cell metabolism, muscle contraction and nerve impulse transmission. The main function of calcium is structural.  The skeleton of a young adult male contains about 1.2kg of calcium.  There is continuous movement of calcium between the skeleton and blood and other parts of the body.  This is finely controlled by hormones.  Metabolites of Vitamin D are important in this, increasing reabsorption of calcium by bones.

Calcium also plays a role in cell biology.  Calcium can bind to a wide range of proteins altering their biological activity.  This is important in nerve impulse transmission and muscle contraction.  Calcium is also needed for blood clotting and activating clotting factors.

Contributing Risk Factors

Some research has indicated that vegetarian women are at less risk of osteoporosis than are omnivorous women.  This is thought to be due to animal protein increasing calcium loss from bones.  However, other research has found no difference between vegetarians and omnivores.

Signs and Symptoms

A low level of calcium in the blood and tissues can cause hypocalcemia.  This involves sensations of tingling and numbness and muscle twitches.  In severe cases muscle spasms may occur, called tetany.  It is more likely to be due to a hormonal imbalance in the regulation of calcium rather than a dietary deficiency.

Excess calcium in the blood can cause nausea, vomiting and calcium deposition in the heart and kidneys.  This usually results from excessive doses of vitamin D and can be fatal in infants.

Treatment and Prevention

People aged 19 to 50 should be getting 1000mg of calcium per day in the form of low oxalate greens, fortified foods or dairy products.  Put another way, if you are aged 19-50 and are not drinking three cups of calcium-fortified soy milk, orange juice or milk, or eating three cups of greens every day then you should consider taking calcium supplements.

During pregnancy, calcium absorption from the gut increases and no additional calcium is generally needed.  Pregnant adolescents are an exception to this, having particularly high calcium needs.  Breastfeeding women need an extra 550mg of calcium daily; a lactating woman can lose up to 300mg per day in breast milk.

The NIH recommends a calcium intake of 1000mg per day for pre-menopausal women and post-menopausal women on estrogen replacement therapy (ERT).  If post-menopausal women are not on ERT, their calcium intake should be 1500mg per day.

Calcium absorption decreases with age so it is important that the elderly receive adequate dietary calcium.

Additional Tips:

• Calcium should ideally be obtained through our diet.  Dairy products are particularly high in calcium and a glass of milk contains about 300mg calcium.
• However, if women are unwilling or unable to obtain enough calcium in their diet, they might consider calcium supplements.
• There are a large variety of calcium supplements available, and if you are searching for one, you should keep in mind the following:
   
  
  • Look for supplements that contain calcium carbonate because they contain the highest percentage of calcium per tablet, are cheaper, and are more widely available.
  • Beware of supplements made of dolomite (limestone) or bone meal because they may be contaminated with lead.
  • There is no advantage in taking supplements that are chelated (bound) with protein.
  • The vitamin D in some supplements is usually not necessary because we normally get enough vitamin D from sunlight, fortified milk and eggs.
• Try to keep total calcium consumption under 2000mg per day.  At higher amounts, there is an increased risk of developing kidney stones.
• To increase the absorption of calcium take smaller amounts more often, such as at meal-times, ratheer than taking one big dose.
• Beware that calcium supplements can decrease the amount of iron you absorb.

Complications

Vitamin D is needed for absorption of dietary calcium and so calcium deficiency may be linked to rickets in children.  In adults, calcium deficiency may lead to osteomalacia (softening of the bones).  This may be related to repeated pregnancy with lengthy breast feeding.

Osteoporosis can be due to calcium deficiency.  This involves loss of calcium from the bones and reduced bone density.  This causes bones to be brittle and liable to fracture.  Bone loss occurs with age in all individuals.  This usually occurs after 35-40 years and involves the shrinking of the skeleton.  Bone loss is greatest in women following the menopause.  This is due to reduced levels of the hormone, estrogen.  Postmenopausal women are particularly at risk from osteoporosis.