The main function of calcium is the development and maintenance of healthy bones and teeth. Bone is made up of cells and fiber embedded in a mineral matrix, which is mostly crystals of calcium phosphate. One form of bone calcium is bound tightly within the bone and the other is easily removed to maintain blood levels. Calcium is removed from the tightly bound part of the bone only when the more mobile stores are exhausted and dietary intake is inadequate. Bones are constantly being replaced with 20% of an adult’s bone calcium reabsorbed and replaced every year.

NERVE AND MUSCLE CONTRACTION - Calcium is essential for muscle contraction, including that of the heart muscle and for nerve impulse conduction. Increasing calcium may normalise heart rhythm in arrhythmia sufferers. Calcium also aids in the release of neurotransmitters which carry messages between nerve cells.

BLOOD PRESSURE - Calcium interacts with sodium, potassium and magnesium to regulate blood pressure. It has been found that people whose diets are low in calcium are more likely to suffer from high blood pressure. The effects of a mother’s high calcium diet during pregnancy may also be passed on to her children who will be less likely to suffer from high blood pressure. major class of drugs used to lower high blood pressure blocks the channels which transport calcium across muscle cell membranes. There is currently an ongoing debate as to whether these calcium channel blockers increase the risk of heart attacks.

BLOOD - Calcium in the blood is essential for clotting by activating vitamin K (prothrombin) which is the first stage in wound healing.

It is also involved in the control of blood cholesterol levels. Increased calcium may lower blood cholesterol levels and reduce the risk of developing premature heart disease.

IMMUNE FUNCTION - Calcium in milk has been shown to enhance resistance to salmonella in rats.

METABOLISM - Calcium is essential for the production and activity of many enzymes and hormones that are involved in digestion, energy and fat metabolism and the production of saliva. Diabetics often have increased levels of calcium in their cells and the resulting disturbance in metabolism may play a role in some of the complications of diabetes such as heart disease and cataracts.

CELL MEMBRANES - Calcium is involved in the transport of nutrients and other substances across cell membranes and aids in the maintenance of connective tissue which holds cells together.

Absorption: Between 10 -40% of dietary calcium intake is absorbed although women after menopause may only absorb 7%. Calcium from milk and milk products is absorbed more easily than that from vegetables. Absorption is enhanced by vitamin D, proteins, lactose, phosphorus, stomach acid and magnesium.

Lactation increases the ability of women to absorb calcium after weaning or the resumption of menstrual periods. Deficiency and moderate exercise also increase absorption and the efficiency of absorption decreases as intake increases.

Dietary calcium must be made soluble in the stomach and then pass to the small intestine where it combines with a calcium binding molecule so it can be absorbed (chelation). Calcium competes with zinc, manganese, magnesium, copper and iron for absorption in the intestine and a high intake of one can reduce absorption of the others.

Adults excrete 400-600mg of calcium daily.

Deficiency: Signs of severe calcium deficiency include abnormal heartbeat, muscle pains and cramps, numbness, stiffness and tingling of the hands and feet and dementia. Children can suffer from rickets, with symptoms of excessive sweating of the head, slowness in sitting, crawling and walking, insomnia and bow legs. In adults deficiency can lead to osteomalacia with symptoms of bone pain, muscle weakness and delayed healing of fractures.

Blood levels of calcium are tightly regulated by hormones, including calcitonin and vitamin D. These hormones control absorption from the gut, excretion from the kidney and the rate of bone formation and breakdown. If there is a calcium deficiency calcium is extracted from the bones to maintain blood levels.

BONES - Osteoporosis, which literally means ‘porous bones’ is the result of calcium deficiency and in some cases, can be so severe as to cause the bones to break under the weight of the body. Particularly badly affected bones include the spinal vertebrae, the thigh bone and the radius (shorter arm bone). The symptoms of osteoporosis may be absent until fractures occur although in some cases there may be back pain.

Postmenopausal women are especially prone to osteoporosis although the problem occurs in a similar way in men. Most of the bone loss seen in osteoporosis occurs in the first 5-6 years after menopause due to a decline in circulating oestrogens and an age related reduction in vitamin D production.

Getting enough calcium early in life is vital for bones to reach their maximum density so that they are strong enough to support the body even when they lose density later in life. Studies show that calcium intake in the 11-24 age group is often below the recommended levels with serious consequences for later life. It is never too late to slow the bone loss seen in osteoporosis and early postmenopausal years are an important time to ensure optimal intake.

There may be a genetic component in osteoporosis but behavioural and hormonal factors. Body weight is the factor most linked to bone mineral density and in women, body fat may be at least as important as muscle in maintaining bone mineral content. Oestrogen replacement therapy, weight bearing exercise, adequate lifelong calcium intake and moderate alcohol intake all play important roles in preventing osteoporosis.

Bone loss is found to be up to 11% greater during the night. Calcium levels are also lowest during the night and may be affected by the concentration of the hormone cortisol. These findings may offer new hope for the treatment of osteoporosis.

DIGESTIVE SYSTEM - Calcium deficiency may also play a role in colon cancer but further studies are necessary to confirm the link. Researchers have found that people who eat a lot of calcium containing foods are less likely to develop colon cancer than those who eat small amounts. Calcium may exert its protective effects by binding to cancer causing bile acids produced in the colon so reducing irritation. Calcium may also normalise the growth of cells in the intestinal wall thus protecting against cancerous changes.

BLOOD PRESSURE - Calcium deficiency can lead to high blood pressure. Increasing intake has been shown to lower blood pressure in cases where there are deficiencies. Whether calcium can lower blood pressure in cases where there are no apparent deficiencies is controversial.

MUSCLES - When calcium levels drop below normal, muscle cramps can occur as low levels of calcium in the blood can increase the sensitivity of the nerves and cause muscles to go into spasm. Pregnant women whose diets are deficient in calcium are at greatest risk of muscle cramps.

TEETH - Calcium deficiency can lead to periodontal disease.

Those at risk of calcium deficiency include the elderly, people who don’t eat dairy products, those on high protein or high fibre diets and those who drink a lot of alcohol. People on weight reducing diets are also at risk as calcium containing foods are often high in calories. Athletes and pre-menopausal women whose menstrual periods have stopped may also be at increased risk of deficiency which can lead to stress fractures, shin splints, weak bones, poor bone healing and eventually osteoporosis.

Studies have shown that calcium is deficient in the diets of may women with around 35% of women suffering from osteoporosis after menopause. The average daily intake in the US is 600mg and in many countries calcium is the mineral we are most likely to be deficient in. Hip fractures cost $10 billion in the US and $175 million per year in Australia.

Supplements:

Pregnant and breastfeeding women, postmenopausal women and vegans may benefit from supplements. Some research shows that taking calcium supplements later in life can slow the bone loss associated with osteoporosis.

Some studies have shown that calcium supplements lower blood pressure in mildly hypertensive patients although the results are controversial. It is possible that supplements can be mainly of benefit in cases where calcium intake is insufficient, which may be relatively common. Increasing calcium intake may increase the excretion of sodium thus reducing blood pressure.

Some calcium supplements can interfere with iron absorption and iron and calcium supplements should be taken at different times although calcium citrate and calcium ascorbate may enhance iron absorption as they are acidic. When taken with magnesium supplements the ratio should be 2:1 calcium to magnesium.

As bone loses calcium at night some experts recommend taking supplements then to maintain blood calcium levels.

Therapeutic uses:

Calcium can be used to control the incidence of leg cramps in pregnant women. It has also been shown to reduce the incidence of menstrual cramps and symptoms associated with premenstrual syndrome.

Use of calcium supplements during pregnancy may lower a woman’s blood pressure and lower the risk of pre-eclampsia which occurs in one in every twenty pregnant women. Symptoms of pre-eclampsia are high blood pressure, headache, blurred vision and anxiety. This can lead to eclampsia, a seizure disorder which can cause complications with pregnancy and even death. Many pregnant women do not consume enough calcium to ensure optimal blood pressure regulation.

Calcium may be of benefit in the treatment of allergy complaints, for depression, insomnia, panic attacks, arthritis, hypoglycaemia, muscle and joint pains.

Recent studies have shown that slow release calcium fluoride therapy can reduce bone fractures and increase bone density in postmenopausal women although other researchers have found that fluoride therapy can lead to calcium deficiency despite calcium supplementation.