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Milk and milk products are the richest dietary sources of
calcium (parmesan, mozzarella, cheddar, Swiss, blue, ricotta,
cottage, ice cream, milk: skim, low fat, whole, yogurt, and
buttermilk). Lesser amounts of calcium are found in
shellfish, egg yolk, canned sardines and salmon (with bones),
soybeans and certain green leafy vegetables such as turnip
and mustard greens, broccoli, collard greens, bock choy,
and kale. Other sources are Brazil nuts, sunflower seeds,
almonds, and red kidney beans. Calcium is also found in
such foods as spinach and rhubarb; however, the presence
of oxalic acid in these foods may bind with calcium
rendering it unavailable for absorption. As a result of
fortification, infant cereals are excellent sources of
calcium. More recently, the fortification of foods such
as cereals, orange juice and flour, as well as the use of
calcium in antacids like Tums and Rolaids, have become
additional sources of calcium in the diet. In hard
water areas,drinking water may also be a significant
What is known to be good for:
Calcium has been found to help weight loss. When dietary
intake of calcium increases, there is also an increase in the
breakdown of fat and a decrease in
the production of fat, and as a result, body fat is lot.
Other functions of Calcium:
Nutritional data also indicate that increased consumption of calcium-containing foods is associated with a reduced incidence of colon cancer. Increasing the dietary calcium intake of these individuals to between 1200 and 1500 mg per day tends to lower their blood pressure.
Lack of Calcium:
The symptoms of calcium deficiency may include: bone pain, pins and needles in the hands and feet, muscle cramps and twitching, convulsions, and osteoporosis.
Low dietary calcium intake may produce rickets in children. Severe calcium deficiency in children may also result in stunted growth, muscle weakness, parathyroid hyperplasia, hyperirritability, tetany and death. In adults a calcium deficiency will exacerbate
osteomalacia caused by vitamin D deficiency. Insufficient dietary calcium is thought to be a factor contributing to osteoporosis. Osteoporosis is characterized by a significant reduction in bone density causing bone fragility and susceptibility to fracture. Osteoporosis is a prevalent disease among older women and, to a lesser extent, older men. To reduce the risk of osteoporosis individuals are advised to ascertain the recommended calcium intake from adolescence and to increase intake after
menopause. As well, physical activity tends to reduce the risk of osteoporosis.
Skeletal demineralization occurs with prolonged immobilization and bed rest, due to large losses of calcium and phosphorus in the urine.
Excess of Calcium can:
Hypercalcemia is usually due to hyperparathyroidism or excess vitamin D. It is also associated with patients having neoplasms with metastases leading to deposition of calcium in the kidneys. Hypercalcemia may result in muscle rigidity, dehydration, lethargy, nausea, vomiting, anorexia and ultimately coma and death.
Do you know where you find Calcium in your body?
More than ninety-nine percent of the calcium is present in bones and teeth as a component of hydroxyapatite crystals-Ca10(PO4)6(OH)2 and amorphous calcium phosphate. The remaining 1% of total body calcium is necessary for a variety of metabolic processes including enzyme activation, hormone function, nerve transmission, muscle contraction, blood clotting and membrane transport. Calcium is present in the blood in several forms. Ionized calcium accounts for 50% of the total plasma calcium and is the physiologically active form of calcium. The remaining calcium is bound to serum proteins (40-45 percent of total plasma levels) or complexed with citrate, bicarbonate or phosphate.
Absorption, Storage and Excretion
Absorption of calcium from the gut is influenced by a number of factors. One of the most important factors is the individual's need for calcium. The body can adapt to a wide range of intakes by altering the efficiency of absorption and excretion. The efficiency of calcium absorption in the gut decreases with age. Calcium absorption is enhanced by an acid pH which keeps calcium in solution. Vitamin D, lactose and certain amino acids such as lysine and arginine, also enhance calcium absorption. Calcium absorption is decreased by foods containing large amounts of phytates or oxalates both of which will form an insoluble calcium salt which is unavailable for absorption. However, this reaction is considered to be of little biological significance if calcium intake is liberal. Excess fat in the diet or impaired digestion of fat may reduce calcium absorption through the formation of insoluble calcium soaps. Increasing dietary protein will increase urinary calcium excretion if phosphorus intake is held constant.
Sources:HEINZ HANDBOOK of Nutrition, 9th. EDITION, Edited by David L.
Yeung, Ph.D. and Idamarie Laquatra, Ph.D., R.D. and
Nutrition for Life, The no-fad, no-nonsense approach to eating well and reaching your healthy weight, LisaHark, PhD, RD and Darwin Deen, MD.
Adapted by Editorial Staff, December 2007
Last update, August 2008
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