Calcium is the most abundant mineral in the body. An average man contains about three pounds of calcium and an average woman about two pounds. Ninety-nine percent (99%) of the calcium in the body is found in the bones and teeth.

Those at risk of calcium deficiency include the elderly, people who don’t eat dairy products, those on high protein or high fiber diets and those who drink a lot of alcohol. People on weight-reducing diets are also at risk as foods containing calcium are often high in calories. Athletes and premenopausal 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.

What does it do for your body?

Bones and Teeth - Calcium is essential in 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. Calcium also aids in the release of neurotransmitters which carry messages between nerve cells.

Blood Pressure - Calcium interacts with sodium, potassium and magnesium to help regulate blood pressure. It has been found that people whose diets are low in calcium have a higher incidence of 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.

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 supports normal blood cholesterol levels and overall heart health.

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.

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 and stomach acid. 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 (a process called 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. 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 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 intestine, 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 estrogens 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 as strong as possible 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 in addition to behavioral and hormonal factors. Body weight is the factor most frequently linked to bone mineral density and in women, body fat may be at least as important as muscle in maintaining bone mineral content. 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 support of osteoporosis.

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

A synthetic calcitonin nasal spray is available in the U.S. and offers and alternative support for osteoporosis for women who cannot tolerate the estrogen therapy that is the conventional support for osteoporosis. Intake of calcium and vitamin D needs also to be adequate.

Digestive System - Calcium may also play a role in colon health but further studies are necessary to confirm the link. Researchers have found that people who eat a lot of foods containing calcium are less likely to develop colon problems than those who eat small amounts. Calcium may exert its protective effects by binding to certain colon irritants. Calcium may also normalize the growth of cells in the intestinal wall thus protecting the colon.

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 since 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's role in tooth development and health are well documented.

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 support normal 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 normalizing blood pressure.

Different calcium supplements contain different amounts of calcium. Carbonate contains 40% calcium, but citrate contain 21% calcium. Calcium gluconate and calcium lactate, the two most soluble forms contain 9% and 13% respectively. Bonemeal and dolomite are common sources of calcium supplements but they may contain lead and cadmium which can be toxic. Antacids are also good sources of calcium but those containing aluminum or sodium should be avoided, since aluminum inhibits calcium absorption and sodium can raise blood pressure. Calcium citrate is an acidified form and may be absorbed better in older people who often have low stomach acid.

Calcium carbonate can be taken in divided doses with meals in order to avoid side effects such as nausea, gas and constipation. Absorption of calcium carbonate may be increased with food while other supplements may be best absorbed if taken between meals, since there may be some reduction in absorption due to the presence in foods containing certain fats and fiber. Another form of calcium supplement, calcium hydroxyapatite, is a naturally occurring calcium phosphorus protein bonded matrix of bone and is the actual protein calcium matrix found in bone.

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 in the evening 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 menstrual muscle tension and stress associated with premenstrual syndrome. Use of calcium supplements during pregnancy may support normal blood pressure and normal delivery.  During pregnancy, the fetus will take calcium at the expense of maternal bones.  Adequate calcium is therefore extremely important during this time.

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. Calcium may also be of benefit in the support of allergies, normal mood and sleep, muscle and joint health.

Interactions

Calcium is regulated by several things: vitamin D, which helps the body absorb calcium and deposit it in the bones; calcitonin, which enhances the ability of the bones to store calcium by transferring calcium from the blood to the bones and inhibiting release; parathyroid hormone, which regulates the transfer of calcium from the bones to the blood; estrogens which help retain calcium in the bones; and thyroid and growth hormones.
In the absence of vitamin D less than 10% of dietary calcium may be absorbed.

Lead absorption is blocked by calcium in the intestines. Boron supplementation may reduce the excretion of calcium. Antacids containing aluminum can inhibit calcium absorption. Excessive calcium can interfere with the absorption of copper, iron, magnesium, manganese and zinc.

Calcium helps in the absorption of vitamin B-12. Calcium and magnesium and calcium and potassium are related in that high levels of one can produce low levels of the other. Excessive potassium can lower calcium levels. Calcium and phosphorus work together to form healthy bones and teeth. If a person's phosphorus intake is too high the body excretes the extra phosphorus and calcium along with it. Vitamins A and C enhance the transport of calcium through cell membranes. Vitamin B-6 may enhance calcium function. High protein diets can increase calcium excretion.

Large quantities of fat, oxalic acid (which is found in chocolate, rhubarb and many dark green leafy vegetables) and phytic acid (which is found in grains) can prevent calcium absorption. Large quantities of sucrose can enhance calcium excretion. The contraceptive pill, anti-epileptic drugs, diuretic drugs, corticosteroid drugs for rheumatoid arthritis, asthma and IBD and some antidepressants can lead to deficiency as can smoking, malabsorption due to lactose intolerance and absorption disorders such as celiac disease. Calcium decreases the absorption of tetracycline antibiotics, iron and aspirin if taken at the same time.

Caffeine and carbonated drinks can lead to calcium losses thus contributing to high blood pressure.

Caution: You should not take calcium supplements if you have impaired kidney function or if you suffer from constipation. 

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