Net Ca Retention Research Articles

Dietary sodium as a risk factor for osteoporosis: where is the evidence?

Na-induced calciuria has been well documented and provides a physiological basis for the proposed role of dietary Na (or salt) as a risk factor for osteoporosis. However, the evidence is based primarily on acute salt-loading studies, and there are insufficient data on the effects of high salt intake on net Ca retention to predict long-term effects on bone health. Results of investigations on salt and bone turnover, as assessed by bone biomarkers, are inconsistent, but the large variations in inter-individual response to acute and chronic Na loading may be related to salt sensitivity. Results of cross-sectional and prospective investigations on high salt intake and long-term bone health are inconclusive, probably reflecting the difficulty of conducting such studies in free-living populations. However, the mean urinary Ca loss of 1 mmol/100 mmol Na suggests that chronic changes in salt intake may have large effects on Ca and bone balance, especially in individuals with a reduced capacity to compensate for Na-induced Ca loss. Investigating the relationship between salt intake and bone health requires a greater focus on whole diets (including components such as K, Mg, P and protein), reliable measures of salt intake, appropriate bone health outcome measures, and improved subject characterisation (e.g. salt sensitivity). The reasons for inter-individual variability should be explored using post-genomic techniques.

Requirement of calcium for commercial broilers and white leghorn layers at low dietary phosphorus levels

Two experiments were conducted to study the requirements of calcium (Ca) for commercial broilers (1–35 day of age) and White Leghorn (WL) layers (196–336 day of age) at a constant levels of phosphorus (P) recommended in the literature. In the first experiment, four levels of Ca (7, 8, 9 and 10 g kg −1) were tested in a maize–soya bean meal and de-oiled rice bran based diets at a constant level of non-phytin phosphorus (NPP) (3.5 g kg −1) with commercial broiler housed in stainless steel battery brooders. The experimental diets were fed ad libitum to 16 replicate groups of six broilers (three males and three female) in each replicate. Level of Ca in the diet significantly influenced the body weight gain ( P≤0.05), serum Ca level, tibia ash contents ( P≤0.01) and retention ( P≤0.05) of Ca and P. The level of Ca in diet did not affect the feed intake, feed per gain, leg abnormality score, net Ca retention and serum P content. The predicted requirements of Ca for maximum weight gain, serum Ca content and tibia ash content were 7.56, 9.72 and 9.83 g kg −1 diet, respectively. In the second experiment, six levels of Ca (32.5, 35, 37.5, 40, 42.5 and 45 g kg −1) were tested in a maize–soya bean meal–sunflower–de-oiled rice bran based diets containing a constant level of NPP (2.8 g kg −1) with layers. The experimental diets were fed ad libitum to six replicate groups (six layers in each replicate) housed in individual cages. Hen day egg production, feed intake, feed egg per mass, shell quality (shell thickness and shell weight), tibia ash content, tibia breaking strength and concentration of Ca and P in serum were not influenced by the level of Ca in the diet. The retention of Ca and P in the broiler experiment and the activity of serum alkaline phosphatase in the layer experiment were inversely related to the level of Ca in the diet. Based on the results, it can be concluded that the requirements of Ca for commercial broilers (1–35 day of age) and WL layers (196–336 day of age) are 7.56 and 32.5 g kg −1 diet, respectively. However, considering the trend seen with serum Ca concentration and tibia ash content in broilers and the activity of serum alkaline phosphatase in layers, it may be desirable to provide 8 and 35 g Ca kg −1 in broiler and layer diets, respectively.

Downward movements of dolomite, kieserite or a mixture of CaCO3 and kieserite through the upper layers of an acid forest soil

Liming and fertilization are important tools for improving the chemical status of acid, base poor forest soils. The downward movement of dolomite, kieserite and a mixture of CaCO3 and kieserite was investigated by monitoring the leachates and exchangeable cation composition from single and combined horizon columns, reconstructed from an acid brown forest soil profile (0-15 cm). Upon entering the soil, Mg ions from kieserite displaced base cations and acidity (H and Al ions) from exchange sites, which subsequently moved down with the mobile SO42- anions. Total leaching during the initial SO42- pulse was similar with the CaCO3 + kieserite mixture. Compared to the single kieserite treatment, the joint application of CaCO3 greatly increased the proportion of Ca in the leachates from all horizons. It also decreased the leaching of acidity from the surface Oe horizon and prevented pH from dropping under this layer. With both treatments, the redistribution of magnesium with SO42- anions resulted in a rapid increase in exchangeable Mg contents throughout the studied columns. Due to the important charge increase in the Oe horizon and to kinetic restraints imposed on dissolution, downward movement of Ca and Mg ions from dolomite was very limited. Mg was however much more mobile than Ca. In the CaCO3 + kieserite and dolomite treatments, the migration of alkalinity and base cations with time was associated with a decrease in exchangeable acidity and an increase in ECEC in the two upper soil layers. By the end of the monitoring period, overall net Mg retention in the 0-15 cm columns increased in the order kieserite < CaCO3 + kieserite << dolomite with respectively 20, 35 and 85% of cumulated inputs remaining in the columns. The corresponding net Ca retention amounted to 82 and 96% of cumulated inputs for the CaCO3 + kieserite and dolomite treatments, respectively. Results from this study complement those obtained in the field by clearly demonstrating the mechanisms involved in the downward movement of some fertilizers commonly used to increase the base saturation of acid forest soils.

Dual Tracer Stable Isotopic Assessment of Calcium Absorption and Endogenous Fecal Excretion in Low Birth Weight Infants

Using a dual tracer (44Ca orally and 46Ca i.v.) stable isotope technique, true dietary Ca absorption, endogenous fecal Ca excretion, and net Ca retention were measured in 12 low birth weight (1426 +/- 260 g) infants fed a high Ca-containing formula. Endogenous fecal Ca excretion averaged 7.2 +/- 4.1% of intake, and exceeded 10% of intake in three infants. Net Ca retention, 103 +/- 38 mg/kg/d, was consistent with previous studies of Ca retention obtained using mass balance techniques and correlated closely (r = 0.98, p less than 0.001) with true Ca absorption but not with endogenous fecal excretion (r = -0.40, p = 0.19). Although endogenous fecal excretion may represent a significant source of Ca loss for some low birth weight infants, these data suggest that net Ca retention in low birth weight infants fed a high Ca-containing formula is primarily determined by the total dietary Ca absorbed.

191 IMPAIRED ABSORPTION OF CALCIUM IN TERM BABIES ON LACTOSE FREE FORMULA (LFF) WITH VITAMIN D REPLETION

Vitamin D independent paracellular and non saturable, mechanism is important for intestinal calcium absorption and decreases in lactose free diets. Ten normal term babies with identical repletion levels of 25-hydroxyvitamin D (25D) were fed sequentially with the same starting formula manufactured under two carbohydrate sources: lactose (SF) and polycose (LFF). A 3-day balance was performed after 6-8 days of adaptation to the new diet. Fecal excretion was significantly higher in LFF; urinary calcium was 2.4(1.5) and 2.1(1.5) mg/Kg/d in both periods. There were no differences in Pi absorption despite calcium changes. Mg retention was not affected by lactose absence. Bowel frequency was 3.3 and 3.0 stool/day in both periods. In plasma only Alk p-ases were slightly raised, but 25D was respectively 20.6(10.1) and 21.3(8.1) ng/mL in both periods. Formulae with polycose as a unique carbohydrate source can reduce in 20% the net retention of Ca, thus promoting osteopenia.

Mineral balance studies in very low birth weight infants fed human milk

Mineral homeostasis often is disrupted in the very low birth weight (VLBW) infant fed either human milk or commercial formula that contains insufficient quantities of available calcium (Ca) and phosphorus (P). Alterations in mineral homeostasis include abnormal patterns of serum (Ca and P concentrations and alkaline phosphatase activity) and urine (Ca and P) biochemical markers, low net Ca and P retentions in comparison with intrauterine estimates of mineral accretion, and decreased bone mineral content. A two-phase study was conducted in our laboratory to test for these alterations in mineral homeostasis. In phase 1, VLBW infants fed a preparation of fortified human milk (either human milk-derived fortifier I or II or cow milk-derived fortifier) or cow milk-based formula specially designed for VLBW infants were evaluated during their hospitalization. In phase 2, after hospitalization, these infants were evaluated during the first 6 months of life when fed either their mother's milk or routine formula exclusively. The bioavailability of Ca and P from the tested preparations varied widely. Although the fortification of human milk resulted in both an improved biochemical pattern and net retention of Ca and P, optimal intrauterine mineral accretion was not achieved in any group tested. Longitudinal assessments of bone mineralization, by single photon absorptiometry, demonstrated that human milk-fed former VLBW infants had reduced bone mineral content. These investigations suggest that former VLBW infants fed human milk exclusively may be at risk for Ca and P deficiencies.

726 BIOAVAILABILITIES OF CALCIUM (CA) AND PHOSPHORUS (P) ARE HIGHER IN FORTIFIED MOTHER'S MILK COMPARED TO COMMERCIAL FORMULA

Bioavailabilities of Ca and P in human milk and commercial formula preparations have not been assessed at similar levels of nutrient intakes. In this study, the utilization of Ca and P was compared during the first two postnatal mo in 2 groups of preterm infants fed either fresh mother's milk fortified with lyophiiized human milk skim fractions and added Ca lactate and P salts (Group FM, birthweight, 1088 ± 53 g; gestation 28 ± 0.3 wk, Mean ± SEM) or a commercial formula designed for preterm infants (Group CM, 1057 ± 49 g; 29 ± 0.2 wk). Two 96-h balance studies were conducted at wk 3 and 7. Similar daily intakes were maintained in both groups: Ca 112 ± 2, P 68 ± 3, and nitrogen 486 ± 6 mg/kg and energy 129 ± 1 kcal/kg. Net Ca retention and absorptions of Ca and P were higher for group FM. The ratio and absolute values of Ca/P retention observed in Group FM approximated estimates of fetal retention more closely than those in Group CM. These results indicate that despite similar levels of intake for both groups, the bioavailability of Ca and P in FM was higher than in CM and that Ca and P adequacy can be maintained in preterm infants for two months when they are fed FM.

The effect of 1-alpha-hydroxycholecalciferol on calcium and phosphorus metabolism in the lactating ewe.

1. The effect of 1-alpha-hydroxycholecalciferol (1 alpha-OH-D3) on calcium and phosphorus metabolism has been studied in ewes at peak lactation by a combination of a mineral balance and a radioisotope technique. 2. The rate of Ca absorption was substantially higher in the treated ewes than in controls. The rates of endogenous loss of Ca into urine, faces and milk, however, were only slightly higher. 3. In consequence, the net retention of Ca was increased and the loss of skeletal reserves of Ca normally associated with peak lactation, prevented. 4. Although the rate of bone accretion increased slightly, the increase in skeletal retention of Ca resulted mainly from a decrease in the rate of bone resorption. 5. This finding conflicts with the generally held belief that bone resorption is increased by cholecalciferol treatment. 6. The rates of apparent absorption and retention of P were increased by the treatment probably as a result of a direct effect of the 1 alpha-OH-D3 on P absorption. 7. These results provide a possible explanationof the beneficial effect of 1 alpha-OH-D3 in preventing parturient paresis (milk fever) in the dairy cow.

Effect of synthetic vitamin D derivatives on calcium and phosphate metabolism in intact vitamin O-replete rats

The effect of various synthetic vitamin D derivatives on calcium and phosphorous metabolism was examined in intact vitamin D-replete rats. 1,25(OH) 2D 3 at 26 pmol/day i.p. increases intestinal Ca and P absorption and urinary Ca excretion but has no significant effect on Ca balance and bone turnover. 24,25(OH) 2D 3 has no effect up to 2,600 pmol/day. 1,24(R),25(OH) 3D 3 at 260 pmol/day has the same effect on Ca metabolism as 2,6 pmol/day 1,25(OH) 2D 3, but has no effect on Pi metabolism. 1,24(S),25-(OH) 3D 3 at 260 pmol/day only increases urine calcium. 260 pmol/day of 1,25(OCOCH 3) 2D 3 has a similar effect as that dose of 1,24(R),25(OH) 3D 3 . while 250H-trans-D 3 at 260 pmol/day has no effect. None of the compounds induced a significant increase in net Ca retention, although 1,25(OH) 2D 3, showed a trend in this direction.

The influence of dietary concentration of calcium and phosphorus on their retention in the body of the growing pig

SUMMARYThree gilts and three castrated males weighing 23 kg live weight were given four semi-synthetic diets containing increasing amounts of Ca and P. The Ca and P contents (% dry basis) and Ca:P ratios for the four diets were A, 0·30, 0·38, 1:1·27; B, 0·58, 0·68, 1:1·17; C, 0·94, 1·13, l:l·20; D, 1·16, 1·47, 1:1·27. Each animal was slaughtered at 41 kg live weight and the whole body contents of Ca and P determined. Six pigs were slaughtered at 23 kg live weight and their bodies also analysed for Ca and P contents. Dietary concentration of Ca and P did not influence rate or efficiency of live weight gain nor carcass characteristics. Net retention of Ca and P increased with increasing dietary concentration of these elements. Analyses of isolated femurs suggested that optimal mineralization of the bone was associated with a net retention of 8·2 g Ca/kg live weight gain. The data were used to calculate a value of 32·9 mg/kg live weight/day for the endogenous loss of Ca in pigs of 23–41 kg body weight. The values have been used to compute a mineral requirement of dietary calcium which is in excellent agreement with that derived from estimates in the literature.

The treatment of osteoporosis with calcium infusions: Clinical studies

An increase in the serum calcium (Ca) concentration normally suppresses parathyroid function and stimulates the secretion of thyrocalcitonin. Hypercalcemia resulting from intravenous administration of Ca should therefore lead to a net retention of Ca. This hypothesis was tested in six patients with osteoporosis. After twelve Ca infusions, four patients showed clinical improvement, net Ca retention, enhanced bone formation and reduced bone resorption and an increase in the gastrointestinal absorption of Ca. These effects persisted for many months after Ca infusions were stopped. If calcium given in this way leads to a prolonged suppression of parathyroid function and a comparably enhanced stimulation of thyrocalcitonin secretion, it may reverse the metabolic errors that constitute osteoporosis.