Adequate Ca Intake Research Articles

Effect of different calcium and phosphorus content in Mexican diets on rat femur bone growth and composition

Mexican diets are high in Phosphorus (P) with Ca/P ratios higher than recommended for optimum bone development. Beans and tortillas are the principal energy sources in the typical Mexican diet and these items are also the contributors of Calcium (Ca) and P. In the typical Mexican diet (vegetable diet of this study), beans contribute substantial quantities of Ca (129 mg/d) and P (266 mg/d) and 274 mg Ca/d and 200 mg P/d for corn tortillas. When milk is included (mixed diet), milk provides, 447 mg Ca/d and 350 mg P/d. The objective of this study was to investigate the effect of different Ca and P content typically found in Mexican diets on the growth and composition of rat femurs. Weanling rats were fed diets with different Ca and P content for 30 days, their femurs were extracted, weighed and the Ca and P content analyzed. Dietary Ca affects bone mass and Ca bone deposition (r=0.96;P<0.05) to a much greater extent than dietary P (r=0.71;P<0.05). Even though the P was higher than Ca in the diets, the femurs had equal molar ratios of Ca and P. Ca and P content in the femur of rats fed both test diets increased but to a much lesser extent than when the animals were fed control diets. The animals fed the negative control diet or a diet deficient in Ca and P, showed a significant loss of both Ca and P in the bone when compared to the initial values (P<0.05). On diets high in Ca, final size was larger and bone weights were larger. The rats fed the test diets had significantly (P<0.05) smaller femurs. The femur weight of the rats fed the vegetable diet did not differ in weight from those animals fed a diet deficient in Ca and P. Populations like Mexicans, who depend on beans and tortillas as their primary source of energy, as well as sources of Ca, in the diet, need to find ways to improve dietary Ca intake. Maintaining adequate Ca intake appears to be more important than Ca:P molar ratios.

Lifetime calcium intake and physical activity habits: independent and combined effects on the radial bone of healthy premenopausal Caucasian women

Lifetime calcium intake and lifetime physical activity (PA) habits of 181 healthy premenopausal Caucasian women (aged 20-50) were studied. Nondominant arm was measured by single-photon absorptiometry at the distal (Dis) or 5-mm site and the midshaft (Mid) or two-thirds site of the radius. Values of bone mineral content (BMC), bone width (BW), and bone mineral density (BMD) were obtained. An intermediate or high lifetime Ca (greater than 500 mg/d) was significantly associated with a greater DisBMC (p = 0.0031), DisBMD (p = 0.0031), MidBMC (p = 0.0015), and MidBMD (p = 0.0015) when adjusted for PA. Similarly, with Ca adjusted for, a high lifetime PA (greater than or equal to 45 min of moderate to strenuous activity four times a week) was significantly associated with greater DisBMC (p = 0.0032), DisBMD (p = 0.0022), MidBMC (p = 0.0012), MidBW (p = 0.0173), and MidBMD (p = 0.0546). These findings suggest important roles for both adequate Ca intake and PA habits in enhancing peak adult skeletal mass and a trade-off between these two variables, when each was intermediate or higher.

Phosphorus and calcium metabolism in growing calves with special emphasis on phosphorus homoeostasis: 1. Studies of the effect of changes in the dietary phosphorus intake on phosphorus and calcium metabolism

SummaryCalves were fed continuously at 4 h intervals a low P basal diet with or without P supplementation to give three levels of dietary P intake: one was deficient in P (2·5 g/day), the second adequate (6·0 g/day) and the third contained an excess of P (10·0 g/ day) according to Agricultural Research Council (1980) recommendations. Once steadystate conditions were achieved (after 2–3 weeks on the diet)32P and46Ca kinetic studies were carried out, together with measurements of P flow rates at the reticulorumen and P and Ca balances. With increased dietary P intake, the amount of dietary P absorbed increased as initially did the efficiency of P absorption. Both the serum P concentration and the rate of P retention increased in direct relation to increased P intake and increased P absorption. Salivary secretion of P increased with increased P absorption and in direct relation to serum P concentration. Endogenous faecal losses of P were also directly related to P intake and P absorption and results suggest that increased loss with increased P intake is inevitable.Despite a constant and adequate Ca intake, the rate and efficiency of Ca absorption, which was low on the low-P diet, increased significantly on the adequate and high-P diets. Similarly, Ca retention increased substantially on the higher P diets, showing that Ca metabolism can be controlled according to P status.

Hormonal alterations in experimental diabetes: role of a primary disturbance in calcium homeostasis.

Chronic diabetes mellitus in the rat is attended by a reduced bone turnover and growth arrest, decreased circulating immunoreactive parathyroid hormone (iPTH), and hypercorticosteronism. Since chronic insulin deficiency in the rat is associated with intestinal hyperabsorption of calcium and a positive calcium balance that may account for the decreased iPTH, as well as other hormonal alterations observed in these animals, we studied the effect of long-term (5 week) dietary calcium restriction (0.1% Ca, 0.8% P) in control and streptozotocin-induced diabetic rats. Chronic diabetic rats reared on a normal calcium (1.2% Ca) diet had increased serum calcium and phosphate (Pi) concentrations and were markedly hypercalciuric and phosphaturic compared with controls. Serum corticosterone was increased and iPTH markedly decreased in the diabetic animals. Dietary Ca restriction (0.1% Ca) decreased urinary calcium excretion and resulted in a comparable phosphaturic response in both control and diabetic rats. Moreover, although Ca restriction in diabetic animals had no appreciable effect on serum insulin, serum glucose, or urinary glucose excretion, it was associated with a marked increase in circulating iPTH; this resulted in serum concentrations comparable with that observed in control animals reared on the low Ca diet. These results support the hypothesis that the decreased circulating iPTH observed in chronic diabetic rats results predominantly from their intestinal hyperabsorption of Ca. In contrast to control animals, diabetic rats reared on a low Ca diet failed to maintain their serum Ca despite the marked increase in serum iPTH and striking decrease in calciuria, thus underscoring the reliance of these animals on intestinal hyperabsorption of Ca to maintain Ca balance under conditions of adequate Ca intake. Serum corticosterone was insignificantly altered by dietary Ca restriction in control rats; hypercorticosteronism, characteristically observed in diabetic rats, was normalized by Ca restriction. We conclude that a primary disturbance in Ca homeostasis may contribute, in part, to hormonal alterations observed in chronic experimental diabetes.

An examination of the calcium and phosphorus nutrition of thoroughbred racehorses.

The calcium and phosphorus nutrition of thoroughbred racehorses was assessed by analysis of serum and urine samples collected from 90 horses in 1975 and 139 horses in 1980-81 at racetracks in Melbourne. Horses that were excreting greater than 15 mumole Ca/mosmole and which had a calcium to creatinine clearance ratio greater tha 2.5% were considered to have adequate Ca intake. Horses that were excreting greater than 15 mumole P/mosmole and which had a phosphorus to creatinine clearance ratio greater than 4% were considered to have excessive phosphorus intake. Sixty-percent of the horses sampled had adequate Ca intake, and 44% had excessive intakes of P. Twenty-five percent of the horses were excreting more P in urine than Ca. This would indicate these horses were subjected to nutritional secondary hyperparathyroidism, and horses entered in races by 53 of 99 trainers were in this category. It may be concluded that a high proportion (40%) of thoroughbred racehorses receive inadequate calcium nutrition while they are fed high-grain diets during racing.

Adaptations in the calcium and phosphorus metabolism of sheep in response to an intravenous infusion of Ca.

1. The effect on calcium and phosphorus metabolism of a high rate of Ca infused directly into the blood of Ca -deficient wethers, already receiving an adequate Ca intake, has been studied by a combination of balance and radioisotope techniques. 2. The rate of Ca retention, which was already high, increased only slightly during the infusion before it reached a maximum. The surplus Ca was compensated for by a decrease in the rate of absorption and an increase in the rate of urinary Ca excretion. 3. These findings support the theory that at maximum retention the rate of Ca absorption becomes regulated according to the rate at which Ca can be stored in bone. 4. results suggest that the decreased absorption was due to a decrease in the rate of active absorption and that the low rate remaining was due to diffusion. 5. The rate of P retention was increased by the Ca infusion, possibly as a result of the increased Ca retention.

The effect of dietary calcium intake of ewes in pregnancy on their Ca and phosphorus metabolism in lactation.

1. A combination of a mineral balance and a radioactive technique has been used to study the effect of the dietary calcium intake of ewes in pregnancy on their Ca and phosphorus metabolism in lactation.2. Ewes which had received a Ca-deficient diet in pregnancy absorbed Ca at a greater rate and with a greater efficiency in early lactation than did the control animals, which had received an adequate Ca intake in pregnancy. The apparent absorption of P was also higher in the Ca-deficient sheep.3. Since both groups of sheep received the same high Ca intake in lactation, the increased rate of absorption of Ca must have resulted from an increased rate of active transport rather than an increased rate of diffusion.4. Retention of both Ca and P was positive in the Ca-deficient ewes but negative in the control ewes. This difference in retention reflected a difference in bone metabolism.5. The maximum rate of absorption possible, which is equal to the rate of irreversible loss of Ca from the rapidly exchangeable pool, was much greater in the Ca-deficient lactating ewes than was previously found in Ca-deficient wethers. This difference is due to the additional pathway of loss of Ca in the milk of the lactating animals.6. The relationship between these findings and the prevention of milk fever in dairy cows by manipulation of the dietary Ca intake is discussed.

The effect of changes of dietary calcium concentration on calcium metabolism in sheep.

1. The effect of changes of dietary calcium concentration on Ca metabolism in eight adult wethers has been studied by the use of balance and radioactive techniques.2. Animals receiving an adequate Ca intake absorbed sufficient Ca to supply their maintenance requirements only; a change in intake resulted in a corresponding change in the rate of absorption and disturbed this Ca balance. The new rate of absorption appeared to be determinded by the Ca concentration of the new diet and the efficiency of absorption of Ca from the previous diet.3. Provided the new diet contained sufficient available Ca, animals quickly altered their efficiency of absorption of Ca until they were again absorbing enough for maintenance only.4. When a lack of available Ca in the diet made it impossible for them to meet their maintenance requirements, they slowly reduced faecal endogenous excretion of Ca.5. Ca-deficient animals absorbed Ca at a very high rate when given a diet plentiful in Ca, and absorption decreased only when all the previous losses had been restored.6. Ca-deficient animals also mobilized Ca reserves more readily in response to a severe loss of blood Ca than did animals which were not deficient.7. Retention of Ca was directly related to the rate of absorption of Ca and inversely related to the rate of resorption of Ca from bone.8. The results indicate that resorption of Ca from bone is the major process involved in Ca homoeostasis and that Ca absorption is responsible for the long-term control of Ca metabolism and in particular for maintaining body Ca reserves.