Calcium dietary recommendations

The mean dietary intake of soy isoflavones in Asian populations consuming soy-based diets ranges from 20-40 mg isoflavones/day, with upper percentile consumer intakes of 70 mg/day (corresponding to around 1 mg/kg body weight). In the six month intervention studies in Western postmenopausal women, the effective dose for improved BMD was around 80-90 mg/day, while in the one year, randomized, double-blind, placebo controlled clinical trial, the effective dose was 54 mg/day. Overall, the dietary recommendation is to consume 50 mg isoflavones/day in combination with standard nutritional requirements for calcium and vitamin D. 

Calcium carbonate is the salt of choice because it contains the highest amount of elemental calcium and is the least expensive (see Table 88-5). The fraction of calcium absorbed is dose-limited, so maximum single doses of 600 mg or less of elemental calcium are recommended. Calcium carbonate tablets should be taken with meals to enhance absorption. Calcium citrate absorption is acid-independent and need not be administered with meals. Although tricalcium phosphate contains 39% calcium, nonabsorbable calcium-phosphorus complexes may limit overall calcium absorption compared to other products. This product may be required for up to 10% of seniors with hypophosphatemia that cannot be resolved with increased dietary intake. Disintegration and dissolution rates vary significantly between products and lots. Products with good disintegration and dissolution rates and lead contents of less than 1 mcg/day should be recommended. 

The diet of rheumatoid arthritis patients should be rich in proteins, minerals, and vitamins all vital to tissue resistance and repair. This calls for plenty of meat, fish, and dairy products, fruits, and vegetables. Liberal amounts of milk and other sources of calcium are recommended. The extra supply of dietary calcium helps avoid the adverse effects of the disease on (1) tissue repair and growth, and (2) bone metabolism and such a diet helps fortify the body against the general debilitation and possible anemia that may accompany rheumatoid arthritis. 

Vitamins, minerals, and electrolytes— Studies have shown that during moderate to severe stresses, more zinc, copper, magnesium, and calcium are lost in the urine. Furthermore, stress results in altered blood levels of vitamins A and C, and of zinc and iron. Also, part of the response to stress includes water and sodium retention, via veisopressin and aldosterone secretion. As for the water-soluble vitamins—thiamin, riboflavin, niacin, pyridoxine (B-6), pantothenic acid, folic acid, and vitamin C stress increases their requirement. However, no dietary recommendations are made for these nutrients for individuals under stressful situations. Still, it seems wise to supply some supplementation before deficiency symptoms appear. 

Nutritional surveys indicate that children of low-income groups consume less than recommended dietary allowances of calcium and iron. Dietary deficiencies of these two minerals have been shown to potentiate the toxicity of lead (Johnson and Tenuta 1979 Yip et al. 1981 Ziegler et al. 1978). Thus, nutrient deficiencies in conjunction with a developmental predisposition to absorb lead makes this subset of children at a substantially elevated risk. More information on children s susceptibility to lead is presented in Section 2.6. 

Dietary intake data for calcium, phytate and phytate/calcium ratio are summarized in Table II. Mean calcium intake for HS-I was about 300 mg greater than the recommended dietary allowance (RDA) of 800 mg established for adults by the National Research Council (8) and for HS-II just slightly less than the RDA. The range of calcium intakes, because of different caloric needs was from 927 to 1490... 

In the studies on humans there appeared to be decreased calcium balances when 200 g or more of spinach per day was included in the diet. In two of the studies in which women were fed spinach, calcium intakes were below the Recommended Dietary Allowance of 800 mg/day (37). Some studies were conducted for short period of a week or less, which may not be sufficient time to adjust to a change in diet. From measurement of calcium excretion in urine after a test meal, it was shown that the calcium in oxalate-containing vegetables was less well-absorbed than that of milk or of vegetables not containing oxalic acid. However, this would not necessarily affect calcium balance, since the total amount of calcium in the diet would have to be considered. The effect of a combination of oxalic acid and fiber on calcium bioavailability should be further investigated. 

It has been well established that the ingestion of high dietary protein levels results in hypercalciuria in man, and that hypercalciuria is frequently accompanied by negative calcium balance (1-3). In a summary of data from nutritional surveys in the U.S., Pao (4J showed that dietary protein intake was well above the Recommended Dietary Allowances (RDA) for both men and women regardless of age (1). Although dietary calcium intakes are generally at the RDA for men, women below the age of 50 yr consume only 75% of the RDA (4J. Women above the age of 50 yr consume only two-thirds of the RDA for calcium (4). These low consumptions become critical when we consider the reduced ability for calcium absorption demonstrated in both men and women over the age of 60 yr (6). 

The recommended dietary allowance, RDA, for calcium In the United States Is 800 mg per day (1) However, this amount of calcium may not be adequate throughout adult life for maintaining the normal skeletal structure and for preventing bone loss with aging, particularly In females Recent studies Indicate that this amount of calcium may not be adequate for maintaining the optimal bone mass which reaches Its peak at the age of 30 to 35 years (2) and decreases thereafter Even If the calcium Intake Is adequate, one has to consider to which extent this amount of calcium Is utilized There may be a decrease In the Intestinal absorption of calcium (3) or the... 

Calcium has earned a reputation as one of the most at-risk nutrients (Foote et ah, 2004) and in 2005 the Dietary Guidelines Advisory Committee classified Ca as a shortfall nutrient because average Ca intake often falls to <60% of the recommended intake in subsets of the population (Kennedy and Meyers, 2005). The pressing need to improve the Ca status of Americans has been highlighted by the Healthy People 2010 Objective, an initiative that endeavors to increase, to at least 75%, the number of US individuals 2 years or older that meet current Ca recommendations (Looker, 2003). The general population requires ongoing education to more fully appreciate the relevance of Ca in relation to current and future health, the imminent risks associated with habitual inadequate intakes, and practical means by which to achieve recommended intakes. 

Looker, A. C. (2006). Dietary calcium Recommendations and intakes around the world. In "Calcium in Human Health" (C. M. Weaver and R. P. Heaney, eds.), pp. 105-127. Humana Press Inc., Totowa, NJ. 

A potential concern has been the dietary ratio of calcium to phosphorus (Ca P) in relation to bone health. Based on data from animal studies and on the relative calcium content in bone, a dietary Ca P ratio of 1 1 to 2 1 is recommended as beneficial for bone mineralization in humans (NAS 1980A Chinn 1981 Linkswiler and Zemel 1979). The Ca P ratio in cow s milk (1.3 1) closely approximates that found in bones. The average American diet is estimated to contain a Ca P ratio of 1 1.6 (Chinn 1981 Greger and Krystofiak 1982) to 1 3 (Linkswiler and Zemel 1979), and if no dairy foods are consumed, it may be as low as 1 4. 

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. 

In mild forms of malabsorption, vitamin D (25,000-50,000 units three times per week) should suffice to raise serum levels of 25(OH)D into the normal range. Many patients with severe disease do not respond to vitamin D. Clinical experience with the other metabolites is limited, but both calcitriol and calcifediol have been used successfully in doses similar to those recommended for treatment of renal osteodystrophy. Theoretically, calcifediol should be the drug of choice under these conditions, since no impairment of the renal metabolism of 25(OH)D to l,25(OH)2D and 24,25(OH)2D exists in these patients. Both calcitriol and 24,25(OH)2D may be of importance in reversing the bone disease. As in the other diseases discussed, treatment of intestinal osteodystrophy with vitamin D and its metabolites should be accompanied by appropriate dietary calcium supplementation and monitoring of serum calcium and phosphate levels. 

Inadequate amounts of dietary calcium contribute to loss of bone mineral density and increased rates of fracture observed in osteoporosis, a disease which afflicts over 40% of postmenopausal women in the developed nations. The primary source of dietary calcium is dairy products (Table 3). The preparation of com meal using calcium hydroxide fortifies this grain. Because the intake of dairy products by adult females is low, their average calcium consumption (550 mg) is well below the recommended 1000 1200 mg. Supplementation with various forms of calcium is pmdent. Fortification of fhiit juices and soft drinks with calcium complexed with citric and malic acids has been achieved. 

The dietary calcium/phosphorus ratio is important for the maintenance of kidney health. Where there is too much phosphate, mineral deposits may develop in the kidneys, in a process called nephiocalcinasis. Female rats are especially prone to nephiocalcinosis, which occurs when the calcium/phosphorus ratio is under 1/0.. For this reason, a recommended Ca/P ratio is 1.66 (the same as 1/0.6) Reeves, 1997). 

Dietary phosphate intake is usually 1.2 to 1.4 g (39 to 45 mmoi)/day, nearly twice the recommended intake, of which approximately 60% to 70% is absorbed, principally in the jejunum. As with calcium, both passive and active transport systems exist 1,25(OH)2D is the prmcipal regulator of the active transport of phosphate. PTH-stimulated synthesis of 1,25(0H)2D thus offsets the phosphaturic effect of PTH. The prevailing serum phosphate concentration also modulates renal 25(0H)D-la-hydroxylase. Phosphate depletion or hypophosphatemia stimulates formation of l,25(OH)2D by the kidneys. In general, at pharmacological concentrations, calcitonin has the opposite effect of PTH. It is unclear, however, if calcitonm has any physiological role in mineral homeostasis in adult humans. 

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