Calcium dietary sources

Vitamin D is not strictly a vitamin since it can be synthesized in the skin, and under most conditions that is its major source. Only when sunlight is inadequate is a dietary source required. The main function of vitamin D is in the regulation of calcium absorption and homeostasis most of its actions are mediated by way of nuclear receptors that regulate gene expression. Deficiency—leading to rickets in children and osteomalacia in adults—continues to be a problem in northern latitudes, where sunlight exposure is poor. 

The final mechanism of action of PTH involves the activation of vitamin D3 through the stimulation of la-hydroxylase in the kidney. In the gastrointestinal tract, vitamin D3 is essential for the absorption of calcium. Enhanced absorption of calcium from dietary sources serves to further increase the concentration of calcium in the blood. Many foods, in particular, dairy products, which are rich in calcium, are fortified with vitamin D. The release of PTH from the parathyroid glands is regulated by plasma calcium levels through negative feedback. A decrease in the level of calcium in the blood stimulates the secretion of PTH and an increase in the calcium level in the blood inhibits it. 

All individuals should have a balanced diet with adequate intake of calcium and vitamin D (Table 3-1). Table 3-2 lists dietary sources of calcium and vitamin D. If adequate dietary intake cannot be achieved, calcium supplements are necessary. 

Lead—calcium—tin alloys beer as dietary source of, 3 588 chemical reactions, 4 525—526 in coal, 6 718... 

Figure 8. Calcium values in vertebrate bone and soft tissue samples versus 6 Ca in dietary source (Skulan and DePaolo 1999). Bone values are systematically about 1.3%o lower than source values. Soft tissue values are more variable. All of the values are hypothesized to reflect the balance between Ca dietary intake and exchange with bone calcium (Fig. 9). The soft tissue values are variable largely because the residence time of Ca in the tissues is short. The high value of the egg white reflects Rayleigh-type distillation the egg white loses light Ca to the shell as the shell forms. The small amount of Ca left in the egg white is highly fractionated. The low 6 Ca value of the seal muscle is interpreted as a sign of distress the seal may have had a dietary Ca deficiency for several days or longer before it died, and hence was deriving most of its Ca from bone dissolution.

Milk is one of the best dietary sources of calcium, not only because of the significant quantity of the mineral present but also because of (1) its calcium-to-phosphorus ratio (1.3 1), which is conducive to optimal skeletal growth, and (2) the presence of nutrients such as lactose and vitamin D in vitamin D-fortified milk, which promote calcium absorption (Ziegler and Fomon 1983 Schaafsma 1983 Renner 1983). 

Certain human populations depend on dietary sources of vitamin D because of insufficient biosynthesis of the vitamin due to inadequate skin exposure to sunlight. The classic symptoms of vitamin D deficiency are rickets in children and osteomalacia in adults. 25-Hydroxyvitamin D3 is the major circulating metabolite in the blood, but the hormonally active form of the vitamin is 1,25-dihydroxyvitamin D3. The latter metabolite stimulates the intestine to absorb calcium and phosphate by two independent mechanisms and acts with parathyroid hormone to mobilize calcium, accompanied by phosphate, from the bone fluid compartment into the bloodstream. 1,25-dihydroxyvitamin D 3 is also involved in the formation of osteoclasts—giant cells that are solely responsible for the resorption of bone matrix (33). Resorption is an essential process for the development, growth, maintenance, and repair of bone. 

Vitamin D. Vitamin D is a steroidlike hormone that can be obtained from dietary sources or synthesized in the skin from cholesterol derivatives in the presence of ultraviolet light. Vitamin D produces several metabolites that are important in bone mineral homeostasis.27,31 In general, vitamin D derivatives such as 1,25 dihydroxyvitamin D3 increase serum calcium and phosphate levels by increasing intestinal calcium and phosphate absorption and by decreasing renal calcium and phosphate excretion.27,46... 

The primary roles and the recommended daily intake of major and trace minerals are listed in Table 38-3. Similar to vitamins, these minerals are typically obtained from dietary sources. Specific minerals may likewise be included in various multivitamins and other dietary supplements, with the intent that these minerals will promote good health and prevent disease. Again, there is generally no need for mineral supplements for most people eating a reasonably balanced diet. On the other hand, mineral supplements can be helpful in specific situations where the body s need for a mineral may exceed dietary supply. Some examples of appropriate supplementation include calcium supplements for people with osteoporosis (see Chapter 31), potassium supplements for people on diuretics (see Chapter 21), and iron supplements for people with certain anemias. Hence, mineral supplements may be helpful in certain individuals, but the dose and type of supplement should be adjusted carefully. 

Nolan CR, DeGoes JJ, Alfrey AC. 1994. Aluminum and lead absorption from dietary sources in women ingesting calcium citrate. South Med J 87 894-898. 

Both the active and passive modes of calcium transport are increased during pregnancy and lactation. This is probably due to the increase in calbindin and serum PTH and 1,25-dihydroxyvitamin D concentrations that occur during normal pregnancy. Intestinal calcium absorption is also dependent on age, with a 0.2% per year decline in absorption efficiency starting in midlife. The fractional absorption of calcium depends on the form and dietary source. Absorption rates are 29% for the calcium in cow s milk, 35% for calcium citrate, 27% for calcium carbonate, and 25% for tricalcium phosphate. Other factors that limit the bioavailability of calcium in the intestine are oxalates and phy-tates, which are found in high quantities in vegetarian diets and which chelate calcium. 

Dietary sources of calcium are dairy products, eggs, green leafy vegetables, broccoli, legumes, nuts, and whole grains. (Less than 30% of calcium in food is absorbed.) Calcium is absorbed in the small intestine. The amount of absorption depends on the serum calcium level and availability of vitamin D. There is reduced absorption of calcium if there is a high serum calcium level or a low vitamin D level. 

A healthy human body maintains a proper acid—alkaline balance primarily by doing two things expelling excess acid through the detoxification organs and neutralizing acid with alkaline substances, such as calcium or magnesium, that have been stored in the body and are derived from dietary sources. 

Oxalate is an end product of metabolism, predominantly derived from breakdown of glyoxylate and glycine. Plasma concentration of oxalate is 1,0 to 2.4mg/L (11 to 27fxmol/L) and it is excreted in the urine at a rate of 17.5 to 35.1 mg/24 hours (200 to 400pmol/24 hours). Only 10% to 15% of urinary oxalate is derived directly from dietary sources. Intestinal oxalate absorption is increased when the availability of calcium in the intestine is reduced. Hyperoxaluria is... 

When there is adequate sunlight, no dietary source of the vitamin is required. Indeed, an argument can be made that the calciferols are not normal components of the diet. In the United States, it is added to milk, other dairy products, and dairy substitutes. Fish is about the only natural food source. Cholecal-ciferol is produced in the body from endogenously synthesized 7-dehydrocholecalciferol (Fig. 8.10). Consistent with a hormone model, excess amounts of cholecalcdferol can result in excess calcium uptake from the intestinal tract, leading to calcification of soft tissues. 

Major dietary sources of calcium are milk and dairy products, such as cheese and yogurt. Cow s milk contains 120 mg of Ca + per deciliter (30 mmol/L) and is now usually supplemented with vitamin D. Sardines (and other small fish whose bones are consumed) and soybean products can provide significant amounts of calcium. Soybean curd, known as tofu and eaten widely in China and Japan, contains 128 mg of Ca " " per 100 g. Dark green leafy vegetables, legumes, nuts, and whole-grain cereal products contribute to dietary calcium. 

Many adnlts who have a lactase deficiency develop the ability to ingest small amonnts of lactose in dairy products without experiencing symptoms. This adaptation probably involves an increase in the population of colonic bacteria that can cleave lactose and not a recovery or induction of hnman lactase synthesis. For many individuals, dairy products are the major dietary source of calcium, and their complete elimination from the diet can lead to osteoporosis. 

Cheese is an important dietary source of several minerals, in particular calcium, phosphorus, and magnesium (Table XV). A 100-g serving of hard cheese provides ca. 800 mg Ca, which represents the Recommended Daily Allowance for most adults (Food and Nutrition Board, 1980). However, acid-coagulated cheeses, e.g.. Cottage, contain considerably lower levels of calcium than rennet-coagulated varieties (Renner, 1987). 

Patient education should include information about dietary sources of calcium, the need to maintain physical activity to avoid bone loss, avoid ovemse of antacids, and chronic use of laxatives. Patients should be taught to use fruits and fiber for improving bowel elimination. Take oral supplements with meals or after meals to increase absorption. 

Uses Foods (dietary supplement, mineral supplement) pharmaceuticals (tablet diluent excipient abrasive in dentifrices calcium/phosphorus source in multivitamins) stabilizer migrating from food pkg. 

Dietary sources of calcium should be reviewed with the patient. 

Dietary sources of calcium should remain a part of the patient s diet even if he or she is taking a calcium supplement. The patient also should have an adequate intake of vitamin D and magnesium. 

Availability values for calcium and phosphorus used by TCORN 6 are constant, at 0.68 and 0.58. This has been criticised as not reflecting differences in availability according to dietary source. For example, NRC (2001) assumes an availability of calcium and phosphorus in forages of 0.30 and 0.64 and concentrates of 0.60 and 0.70 respectively, although data supporting these coefficients are limited. 

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