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All About Calcium

Facts About Calcium
Calcium Absorption into the body

Osteoporosis
How Hormones Control Calcium In Bones
Types of bone
Too thin or Too much exercise?

How much calcium?
Sources Of Calcium

Facts About Calcium

The body needs a constant level of calcium in the blood for the normal action of nerves and muscles. A hormone released from the parathyroid gland controls this level by balancing calcium from the diet with stores in bones. If there is not enough in the diet, the parathyroid hormone stimulates the release of calcium from the bones. If there is more calcium than is needed to keep the blood level constant, the excess can be deposited in bones. Greater withdrawals than deposits result in the bones gradually becoming less and less dense until they are so chalky that they fracture from a slight fall, or just with the effort of standing. The loss of calcium happens so slowly that it is many years before weakness and chalkiness eventuate. There are no symptoms before the final straw causes a fracture to occur.
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Calcium Absorption into the body

A number of factors govern calcium absorption into the bones. The positive factors which are essen­tial for its occurrence, include:-

  • Calcium in the daily diet .
  • Normal levels of hormones (these are vital for calcium to be retained by bones).
  • Weight-bearing exercise (cal­cium goes into bones when muscles exert a pull on the bone during physical activity) .
  • Vitamin D. (Usually from sun­light on the skin).

Some factors also work against calcium retention. These include: -

  • Too much salt (increases loss of calcium in urine) .
  • Too much protein (reduces retention of calcium.
  • Nicotine from cigarette and cigar smoking.
  • Very high levels of caffeine or alcohol. (Small quantities are not a problem).

The chemical form of calcium may also be important. For ex­ample, we know that the type of calcium in milk and in dairy products is well absorbed. We do not yet know if the calcium in products such as soy milks is ab­sorbed to the same extent.

Small, lightweight women have a lack of body weight and always have less pull of muscle on bone with weight-bearing exercise. They are more prone to weak, porous bones.

Blood tests are of little use in determining calcium levels in the bones, because, the body keeps its levels of blood calcium normal by withdrawing calcium from the bone. Blood tests are therefore; normal, even when bones are dangerously thin. A special type of X-ray machine is needed to measure bone density. Such tests are expensive but are recom­mended for women with a family history of fragile bones or spinal or hip problems.
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Osteoporosis

The condition of porous bones is called osteoporosis. It is very com­mon in older women and is re­lated to the fall in oestrogen levels that usually occurs at menopause, accompanied with a low-calcium diet, a lack of weight-bearing exercise and smoking. At the beginning of the 20th cen­tury, life expectancy for women was about 50 years, so few women lived long enough to develop osteoporosis. Over the past 20 or 30 years, many women have stopped working hard physi­cally, no longer make a daily walk to the shops and carry home their food supplies and have less cal­cium in their daily diet.

Among women, one in five can expect to be hospitalized for a severe fracture to the hip or spine between the ages of 50 and 70. This is a great expense for the community and an enormous bur­den for the many women who must endure the pain of such calamities. As many as 40 per cent of all women can also expect to fracture wrists, ankles and other bones as a result of a slight fall at some stage in their life. Os­teoporosis is also the reason why many older people become stooped, have back problems and appear to shrink with age. “Dowager’s hump” is often the first sign of osteoporosis.
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How Hormones Control Calcium In Bones

In growing children, growth hor­mone ensures that calcium is deposited into bones. In adults, the sex hormones take over this role. At menopause, when the oestrogen levels fall, calcium is no longer retained by the body. This may also occur in younger women and in female athletes if they lose so much body fat that their hor­mone levels change and their periods stop.

Osteoporosis also occurs in men, although the much slower loss of hormones and shorter life expectancy make it more rare. Women at greatest risk of os­teoporosis are those who:-

  • Have had a low calcium in­take throughout their life.
  • Are small and/or light.
  • Have had little weight-bearing exercise.

To maintain bone density in women, most experts now recom­mend that those at risk of os­teoporosis ask their doctor for hormone replacement therapy (HRT). This will cause their periods to continue past the usual menopause age but as they will be slight and regular, many women find it is worth the inconvenience to maintain their bone density.
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Types of bone

There are two types of bone to consider in osteoporosis. Cortical bone in the long bones of the arms and legs is lost when there is insuf­ficient calcium in the blood and the parathyroid hormone causes it to be withdrawn from the bone. Cor­tical bone is also lost if we are lacking in vitamin D (from the sun). Trabecular bone is spongy bone, which is found in areas such as the spine. It is lost when hor­mone levels change and when the diet contains too much salt. Over a lifetime, women lose half their trabecular bone and one third of their cortical bone.
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Too thin or Too much exercise?

Dieting disturbs the hormone balance. Losing body fat often causes periods to stop. When this occurs, trabecular bone from the spine is lost. Strenuous exercise can have the same effect.

This does not mean that women should stay fat and not exercise. Sensible, moderate dieting and in­creased exercise have a positive ef­fect on health.

Girls and women with anorexia nervosa lose substantial amounts of bone and are at high risk of crushed vertebrae and other spinal problems and fractures. There is no evidence that a change to a better diet can undo the damage caused by periods of such intense dieting.
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How much calcium?

The amount of calcium recom­mended varies. In most countries, dietary intake levels of 800-1200 mg are recommended.

Many people think calcium is only important while children are growing. However, calcium con­tinues to be absorbed into bones and peak bone density is not achieved until age 30-35 years. Women have so many bone problems after menopause that all young women and teenage girls should make sure they have plenty of calcium, some weight-bearing exercise and normal hormonal levels. Women should not become so thin that their periods stop.

 

General Recommendations for 
Calcium Intake

Age Group

Calcium  (mg)

Infants (0-6 months)

Breast fed

300

Bottle fed

500

Infants, 7-12 months

550

Children

1-3 years

700

4-7 years

800

Boys

 

8-11 years

800

12-15 years

1200

16-18 years

1000

Girls

8-11 years

900

12-15 years

1000

16-18 years

800

Men, all ages

800

Women

Upto menopause

800

After menopause

1000

During pregnancy

1100


 

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