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Blood calcium concentration is closely regulated by intake control at the
bowel wall, active deposits and withdrawals from bone, and close monitoring of
the amount the kidney excretes. Calcium absorption from GI tract is regulated by
vitamin D and parathyroid hormones. Without parathormone, you cannot actively
transport calcium through GI tract. Each mineral works best in proportion to
other minerals. Vitamin D and calcium intake recommendations must
therefore take into account the kind of calcium, the amount of vitamin D in the
diet, the amount of sun exposure, the activity of parathormone, the dietary
intake of binding substances like Phytic acid, and competition of calcium with
phosphorus, magnesium and other minerals.
If blood calcium drops even marginally, a state of nervous and muscular
hyperactivity - tetany - quickly appears. You can induce tetany in a few minutes
by hyperventilating. The increased gas exchange in the lung lowers blood carbon
dioxide (as dissolved bicarbonate), raises the blood pH, lowers the calcium
concentration, and you are shaky, anxious, with hand muscle cramps drawing your
fingers into a clenched fist. You may wake up at night after hyperventilating in
your sleep with cramps and muscle spasm from abruptly falling serum calcium
concentration. Taking extra calcium may not correct the tetany of
hyperventilation (especially at night) because the blood pH change is a sudden
and powerful controller of calcium concentration, and oral intake of calcium the
previous day is not. The solution for hyperventilation tetany is to rebreathe in
a paper bag, since this causes rapid re-accumulation of blood carbon dioxide,
normalization of the pH and calcium concentration.
Osteomalacia or Osteoporosis ?
Bone stores 99% of body calcium and calcium salts, laid down in a soft
protein matrix , are responsible for the hardness of bones. Long-term calcium
deficiency leads to bone thinning or osteomalacia. Osteomalacia refers to the
reduction of the mineralization of bone. The problem of demineralization of bone
is confused with loss of whole bone tissue (osteoporosis.)
An adaquate calcium intake and adequate Vitamin D will promote optimal bone
mineralization in youth and decrease the rate of bone-mineral loss in the later
postmenopausal period. Lack of Vitamin D in children leads to Rickets -soft,
poorly mineralized bone that bends easily. In older women, a high plasma level
of vitamin D enhances calcium absorption, whereas high sodium, protein, alcohol
and caffeine intakes will cause increased urinary losses and negative calcium
balance. Other regulatory changes and/or vitamin D deficiency may alter the
balance between calcium absorption from the bowel and excretion from the kidney.
The term "Osteoporosis" refers to a loss of total bone mass and not just bone
thinning due to calcium deficiency. Bone loss in adults increases the risk of
bone fractures and may contribute to the loss of teeth in healthy postmenopausal
women. Low bone mass in women is attributed to heredity, estrogen deficiency and
lack of regular physical activity.
Osteoporosis is more a problem of disuse atrophy, with age-related reduction
of bone growth-factors than of calcium deficiency. Women, fearing the stooped
posture of old age, are eager to take milk or calcium supplements. TV ads,
promoting calcium ingestion, show the degenerating profiles of an aging woman
and are deceptive. Women over 50 years of age show the most bone thinning
because of deficiency of anabolic sex hormone production, especially estrogen
and declining physical activity. In early menopause, estrogen replacement is
effective therapy for conserving bone mass in women. Daily,
weight-bearing exercise is the best method of maintaining bone-growth at any age.
Postmenopausal women given calcium alone show progressive bone
de-mineralization.
Measuring Bone Mineral Density is "a poor way of predicating which
woman will suffer from a hip or spinal fracture..." according to Dr. Ken Basset
of the B.C. Office of Health technology assessment. An English study ( Law et al
Br. Med J,1991:303:453-9) showed that low bone density measurements only
identified 6% of women who later suffered fractures. The lifetime risk of hip
fracture in women is about 18% and the incidence increases with age. One
of the reasons for doing a bone density measurement is to focus attention
the need for preventive strategies in postmenopausal women. The test can be
replaced by a policy that states that all postmenopausal women need preventive
strategies, starting with daily exercise and proper nutrition.
Calcium supplements vary. The cheapest, common supplement is Calcium
Carbonate ("Tums"), made from limestone, or oyster shells. The range of
absorption efficiency is great, 7% to 68% in one study. There are problems with
this calcium supplement in large amounts over a long period of time. Calcium
carbonate is an antacid which reduces stomach acidity and may interfere with the
digestion of food. It causes "rebound" hyperacidity after it leaves the stomach.
It blocks its own absorption. It may be poorly absorbed, and bind other minerals
and vitamins. Excess calcium is likely to appear as kidney or gall-bladder
stones. More soluble calcium compounds are better, but are usually more
expensive. Calcium citrate is not soluble. Calcium glycerophosphate is a
soluble compound used in Alpha Nutrition Formulas
Calcium intake recommendations, to be realistic and effective will have to
take into account the type of calcium chosen and the variables of absorption in
each individual. Calcium absorption from GIT is regulated by vitamin D and
parathyroid hormones. Without parathormone you cannot actively transport calcium
through GIT. In normal circumstances less than 1.0 grams of calcium per day is
adequate, but without parathormone, 4-6 grams (calcium citrate) per day may be
required along with excessively high doses of vitamin D, up to 50,000 IU per day
- 250 times the RDA!
Each mineral works best in proportion to other minerals. Calcium is usually
referred to magnesium; and the ratio range should be about 2-1; Ca/Mg. Calcium
intake recommendations must therefore take into account the kind of calcium, the
amount of vitamin D in the diet, the amount of sun exposure, the activity of
parathormone, the dietary intake of binding substances like phytic acid, and
competition of calcium with phosphorus, magnesium and other minerals. Deciding
calcium intake recommendations, is not simple. There is likely to be a wide
margin of error in any general "recommended daily allowance".
From Nutrition Notes
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