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Calcium
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. 99% of the
calcium in the body is found in the bones and teeth.
What! does it do for
your body?
BONES AND TEETH - 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 normalize 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 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 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 behavioral 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.
A synthetic calcitonin nasal spray is available in the US
and offers and alternative treatment for osteoporosis for
women who cannot tolerate the estrogen therapy that is
the conventional treatment for osteoporosis. Intake of
calcium and vitamin D needs also to be adequate.
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 normalize 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 fiber 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 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.
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.
Different calcium supplements contain different amounts
of calcium. Calcium carbonate and calcium citrate contain
40% calcium. Calcium gluconate and calcium lactate, the
two most soluble forms contain 9% and 13% respectively. Bone meal 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 as aluminum inhibits calcium absorption and
sodium can raise blood pressure.
Calcium citrate is an acidified form and is therefore
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 as there may be some
reduction in absorption due to the presence in food of
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. Calcium hydroxyapatite, which is found in bone meal, may actually
restore 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 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
preeclampsia which occurs in one in every twenty pregnant
women. Symptoms of preeclampsia 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, hypoglycemia, 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.
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, oestrogens 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. Aluminum containing antacids 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 B12.
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 your phosphorus intake is too high
your body excretes the extra and calcium along with it.
Large quantities of fat, oxalic acid, (which is found in
chocolate and rhubarb) and phytic acid, which is found in
grains can prevent calcium absorption. Large quantities
of sucrose can enhance calcium excretion.
Vitamins A and C enhance the transport of calcium through
cell membranes. Vitamin B6 may enhance calcium function.
High protein diets can increase 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, mal-absorption due to lactose
intolerance and absorption disorders such as coeliac
disease.
Calcium decreases the absorption of tetracycline
antibiotics, iron and aspirin if taken at the same time.
Caffeine and fizzy drinks can lead to calcium losses thus
contributing to high blood pressure.
Cautions:
You should not take calcium supplements if you have
impaired kidney function or a history of kidney or
bladder stones or if you suffer from constipation. High
calcium intakes increase urinary excretion and increase
the chance of forming kidney stones.
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