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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 adequate 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 required to maintain bone strangth 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".
Vitamin K deficiency is associated with low bone mineral density and increased risk of bone fracture. Arterial calcification and osteoporosis occur frequently in postmenopausal women. While osteocalcin is the main target for Vit K activity, matrix Gla protein (MGP) synthesized by chondrocytes and vascular smooth muscle cells, inhibits tissue calcification, but requires carboxylationto function. Arterial calcification occurs both in the media and the intima or arterial walls. Medial calcification (Mönckeberg's arteriosclerosis) is independent of atherosclerosis. MGP is expressed at both sites. Increased MGP expression in vascular smooth muscle is a potent inhibitor of vascular calcification. Extensive arterial calcification was found in animals that do not express carboxylated MGP
Shiraki et al measured the circulating concentrations phylloquinone (K1) and menaquinones (MK-4) and (MK-7) in 396 Japanese women and related these results with osteocalcin, calcium, and phosphorus; bone-derived alkaline phosphatase activity. They found that ostocalcin activity was increased by higher K1 and MK-7 levels. The K requirement increased with age. They concluded that circulating vitamin K concentrations in elderly people should be kept higher than those in young people. Menaquinone plus vitamin D supplements reduced bone loss in another study.
Arterial calcification occurs with and without atherosclerosis. Higher vitamin K2 intake may reduce or prevent arterial calcium deposits.
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