Enhance Calcium Absorption Research Articles

Intestinal Absorption of Carbohydrates and Calcium: A Review

AbstractA review is given of recent publications on the absorption of carbohydrates especially in relation to calcium. Starch and sucrose are hydrolyzed in mammals by enzymes attached to the wall of the jejunum to glucose and fructose. These are rapidly absorbed via carrier mediated mechanisms in adjoining epithelial cells. Feeding relatively high levels of lactose, sugar alcohols or modified starches to rodents leads to enhanced calcium absorption in the ileum. This results in increased urinary calcium, which may lead to lesions of the kidneys and adrenals in rats or to the formation of bladder stones in mice. If not hydrolyzed to absorbable moieties in the small intestine, carbohydrates pass to the cecum where they are fermented by microbial flora. This fermentation leads to cecal enlargement, diarrhoea and a decrease in urinary pH. All these effects, mainly caused by substantially overfeeding the rodents with these carbohydrates, are of no significance to humans consuming a balanced diet.

Calcium in the Diet: Food Sources, Recommended Intakes, and Nutritional Bioavailability

Calcium nutritional status among some groups in the United States is suboptimal when judged by calcium intakes and the high prevalence of osteoporosis. Unfortunately, however, it is not clear that increases in calcium intake will have a significant impact on osteoporosis or other chronic diseases that have been linked to calcium nutriture. There is still considerable controversy surrounding the issue of calcium RDAs. The body's ability to adapt to varying levels of calcium intakes, the lack of sensitive indicators of calcium status, and the complexity and slow progression of chronic diseases such as osteoporosis make it very difficult to establish the role of diet in this regard. Great progress has been made in the study of calcium absorption. Much is known about the mechanisms involved in calcium absorption and its regulation. Thus, a rapidly advancing field and further developments will be invaluable to our understanding of the role of diet in calcium nutrition. Calcium bioavailability is affected by diet composition and the chemical form of calcium in foods. The calcium in dairy products is readily absorbed in the intestine. Lactose enhances calcium absorption efficiency under some conditions. Components of plants such as fiber, phytate, and oxalic acid may depress calcium absorption. High intakes of protein increase urinary losses of calcium but this effect may be partially offset by the phosphate association with most high-protein foods. Calcium absorption from salts used in supplement tablets is generally good. Absorption from salts such as calcium carbonate which require acid for dissolution may be poor in persons with achlorhydria unless the tablets are consumed with a meal. The practical significance of factors that may alter calcium bioavailability in normal mixed diets is difficult to assess. It may be a significant factor when calcium intakes are marginal or when absorption by the active transport, vitamin D-dependent process is impaired or not fully developed, i.e., it may be significant when vitamin D status is poor, in the elderly, and in young infants.

Increased intestinal absorption of calcium in young and adult X-linked hypophosphatemic mice after the administration of 1,25-dihydroxyvitamin D3.

We have reported that X-linked hypophosphatemic (Hyp) and normal mice respond equally to the administration of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] with uptake of 45Ca from an oral test meal as judged by the isotope remaining in the fecal samples. To determine whether this was due to specific stimulation of calcium absorption, as opposed to changes in calcium secretion or transit time, 1,25(OH)2D3 was administered to 4-week-old (young) and 13-week-old (adult) normal and Hyp mice at a dose of 0.12 micrograms/kg per day by continual infusion from an Alzet minipump. After 3 days of infusion, absorption of 45Ca from the isolated duodenum was measured in situ. Malabsorption of calcium was shown in vehicle-treated 4-week-old Hyp mice by significantly more 45Ca remaining in the intestinal segment and by significantly reduced plasma levels and reduced skeletal levels of 45Ca. Treatment of the young mice, both normal and Hyp, with 1,25(OH)2D3 resulted in increased absorption of 45Ca, increased plasma 45Ca, and increased incorporation of 45Ca into the femur. The young Hyp mice treated with 1,25(OH)2D3 showed a significant increase in femoral ash weight. At 13 weeks of age both normal and Hyp vehicle-treated mice showed equivalent absorption of calcium, and both responded to 1,25(OH)2D3 administration with enhanced calcium absorption. At both ages plasma phosphate rose in only the Hyp mice treated with 1,25(OH)2D3, whereas plasma and urine calcium were increased in only the hormone-treated normal mice. In conclusion, 1,25(OH)2D3 stimulates the absorption of calcium in the isolated duodenum of the young Hyp mouse with equal potency to that of young normal mice.

Effect of lactose hydrolysis on calcium absorption during duodenal milk perfusion.

A multi-lumen intubation system was used to study the absorption of calcium, glucose and galactose in 13 human subjects. The intubation was placed between the duodenum abdomen and proximal jejunum and the subjects were perfused with milk and lactase-supplemented milk. Lactose disappearance over a 20 cm length of intestine was used as the index of lactase activity. The subjects were assigned to one of two groups, lactase-normal and lactase-deficient. There was linear correlation between the absorption of calcium and lactose: lactase-deficient subjects absorbed less calcium than lactase-normal subjects. Perfusion with lactase-supplemented milk enhanced calcium absorption in lactase-deficient subjects but had no effect on that of normal lactase subjects. All subjects absorbed approximately the same percentage of perfused calcium (24%) when perfused with hydrolysed milk. These data indicate that the enhancement of calcium absorption is not a function of lactase per se, but of its hydrolytic products, glucose and galactose.

Tumoral Calcinosis: Clinical and Merabolic Response to Phosphorus Deprivation

Two patients with extensive tumoral calcinosis were treated with aluminium hydroxide. Initial metabolic studies showed positive calcium and phosphorus balances which became negative with aluminium hydroxide treatment. One subject, who had renal impairment, developed transient hypercalcaemia, parathyroid suppression, low levels of 1,25-dihydroxyvitamin D and calcium malabsorption during treatment with aluminium hydroxide. The second patient developed calcium malabsorption due to vitamin D deficiency. When she was replete with vitamin D there were supranormal levels of 1,25-(OH)2D in the serum and enhanced calcium absorption during treatment with aluminium hydroxide. Both subjects developed hypercalciuria and there was dissolution of many of the calcific tumours. The patient with renal impairment accumulated aluminium in the bone.

Effects of taurodeoxycholate on in vivo water and solute transport in rat jejunum in absence and presence of calcium.

Bile acids and fatty acids enhance the permeability of brush-border membrane vesicles for calcium. It has been postulated that increased influx of calcium into the enterocyte might be responsible for the fluid secretion induced by dihydroxy bile acids and fatty acids. During in vivo perfusion studies of the rat jejunum, 15 mM taurodeoxycholate induced secretion of electrolytes and water (P less than 0.001), reduced glucose absorption (P less than 0.001), and enhanced the absorption of mannitol (P less than 0.0125) and calcium (P less than 0.001). Calcium absorption continued to be enhanced during perfusion of a CaCl2-containing solution following the perfusion with taurodeoxycholate (P less than 0.05). In view of the previously demonstrated enhanced permeability of the apical brush-border membrane in the presence of bile acids, it is very likely that some calcium enters the enterocyte along the steep concentration gradient in the presence of taurodeoxycholate. In spite of enhanced calcium absorption, 15 mM CaCl2 had no effect on control absorption rates or on fluid secretion induced by taurodeoxycholate. The data indicate that the effects of bile acids on intestinal transport are not mediated by an influx of calcium into the enterocyte.

Casein phosphopeptide (CPP) enhances calcium absorption from the ligated segment of rat small intestine.

A casein phosphopeptide (CPP) was prepared from beta-casein of cow's milk and the effect of this peptide on the absorption of calcium from a ligated segment of rat small intestine was investigated. CPP injected into a ligated loop of rat small intestine enhanced absorption of calcium from the loop and augmented the deposition of calcium in the femur. Furthermore, CPP inhibited the precipitation of calcium phosphate in vitro, suggesting that this peptide enhances calcium absorption from the small intestinal lumen by increasing the concentration of soluble calcium. This new evidence confirms our previous hypothesis that CPP is an important factor in raising the availability of calcium in milk.

Effect of meal composition on calcium absorption: Enhancing effect of carbohydrate polymers

Meal components including fat, fiber, and carbohydrates can influence the intestinal absorption of calcium; such interactions may be of even greater importance in the presence of intestinal disease. This study compares intestinal absorption of 47CaCl2 administered in four ways: in water, within a standard meal, with a liquid formula (Ensure, Ross Laboratories, Columbus, Ohio), or with a glucose polymer solution (Frodex-15, Ross). Studies were carried out in 9 patients with ileal resection, 3 patients with jejunoileal bypass, and 14 controls. Fractional calcium absorption from water was lower in patients than in controls. Absorption was enhanced 1.5- to 5-fold when 47CaCl2 was administered with a liquid formula diet containing a glucose polymer or with the glucose polymer alone. Patients with the lowest calcium absorption from breakfast showed the greatest effect of calcium ingestion with formula or glucose polymer. These findings further emphasize the importance of meal composition on calcium absorption and provide a possible mechanism for enhancing calcium absorption in some patients with chronically impaired absorption.

Role of prolactin in vitamin D metabolism and calcium absorption during lactation in the rat.

Intestinal calcium absorption and plasma levels of 1,25-dihydroxycholecalciferol (1,25(OH)2D3) were measured in lactating and non-lacting rats and the effects of bromocriptine and exogenous prolactin treatment were evaluated. In lacting rats calcium absorption and plasma levels of parathyroid hormone, 1,25(OH)2D3 and alkaline phosphatase activity were significantly increased. Bromocriptine treatment significantly reduced the enhanced calcium absorption and levels of plasma 1,25(OH)2D3 and alkaline phosphatase but had no significant effect on plasma levels of parathyroid hormone. Prolactin administered with bromocriptine to lactating animals prevented all the changes observed with bromocriptine treatment alone. It was concluded that the increased plasma levels of prolacting during lactation lead to high plasma levels of 1,25(OH)2D3 which are responsible for the enhanced intestinal calcium absorption.

Calcium metabolism during lactation: enhanced intestinal calcium absorption in vitamin D-deprived, hypocalcemic rats.

Lactating rats fed a vitamin D-containing diet maintain elevated serum levels of 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] and increased intestinal net calcium absorption (as a percentage of the intake). Rts deprived of vitamin D for only 2 weeks during lactation lack elevated serum levels of 1,25-(OH)2D3 and develop marked hypocalcemia. We have now determined net absorption of Ca for a 3-day period at the end of lactation in rats suckling a second litter of 10-day-old pups. The rats were fed diets containing either no vitamin D (--D) or 5 IU vitamin D3/g diet (+D) from the sixth day of pregnancy. Net Ca absorption was at least 2-fold higher in +D-fed lactating rats than in nonlactating controls. Vitamin D-deprived lactating rats had values approximately the same as the +D-fed lactating rats, even though the former were severely hypocalcemia and lacked elevated levels of 1,25-(OH)2D3 in plasma and intestinal mucosa. The high efficiency of intestinal Ca absorption in --D lactating rats was confirmed in vitro with everted duodenal sacs which developed essentially the same high Ca concentration ratios across the intestinal wall as did sacs from +D rats. Parathyroidectomy did not significantly affect the Ca concentration ratio of sacs obtained from --D lactating rats 2 days after the operation. We conclude that during lactation, 1,25-(OH)2D3 is primarily required for calcium homeostasis, and enhanced calcium absorption does not require elevated serum and intestinal levels of 1,25-(OH)2D3.

Effects of casein and fibrin on calcium absorption and calcium homeostasis in the rat.

To test the hypothesis that individual proteins have specific effects on calcium absorption, two proteins, casein and fibrin, were pair-fed in diets to rats for 3 weeks. Each protein was fed at normal (1.2%) and low (0.02%) calcium intakes. Diets were matched in other nutrients. Calcium absorption, measured in vitro as serosal-to-mucosal concentration ratio of 45Ca developed by duodenal sacs, was the same for both protein groups when calcium intake was normal and was increased by both low-calcium diets. Comparing low-calcium diets, absorption was greater in fibrin-fed than casein-fed groups. Balance studies showed that casein- and fibrin-fed rats taking normal calcium diets excreted the same amounts of calcium and phosphorus in urine and feces. Fibrin-fed rats taking low calcium excreted twice as much calcium as casein-fed rats and had decreased serum calcium. The balance data suggest that, compared to casein, fibrin prevents absorption or promotes excretion of calcium when calcium intake is low, and the response to calcium depletion is enhanced calcium absorption. It is concluded that individual proteins can alter calcium transport through effects on overall calcium homeostasis.

The influence of phosphorylable molecules on calcium transfer in the rat ileum

Amino or hydroxylated molecules have been tested from both points of view of their effect on calcium absorption in ileal loops, and of their ability to be phosphorylated. Some molecules, very effective in enhancing calcium absorption, are also highly phosphorylable: aspartic and glutamic acids and creatine. Other molecules, virtually ineffective, are not phosphorylable: L-alanine, L-valine, asparagine and glutamine. Ileal mucosa extract induces transphosphorylation from ATP to lysine and arginine, the amino acids the most potent in increasing calcium absorption. The observation that both isomers of the same ose (D- and L-xylose) or that a non absorbable polyoside (raffinose) increase calcium absorption may be linked to the fact that all are phosphorylated in vitro by a purified ileal phosphatase. Injection of either sorbitol or creatine into an ileal loop induces formation of their phosphorylated derivatives, thereby providing circumstantial evidence for a direct relationship between the phosphorylation ability of these molecules and their involvement in calcium transfer mechanisms.

Influence of glucose, fructose, and water movement on calcium absorption in the jejunum

The first experiment demonstrated that glucose stimulated calcium absorption. Possible mechanisms include: (a) glucose stimulation of active calcium absorption, (b) glucose stimulation of water absorption with enhanced calcium absorption by solvent drag, or (c) glucose stimulation of water absorption caused an increased luminal calcium concentration with resultant increased active and/or passive calcium absorption. In a second experiment, neither glucose, fructose or water absorption stimulated calcium absorption when luminal calcium concentration was maintained at a constant level. These results suggest: (a) glucose and fructose indirectly enhance calcium absorption via an effect on water movement, (b) water absorption enhances calcium absorption by virtue of concentrating unabsorbed calcium within the intestinal lumen, not by solvent drag, and (c) bulk water movement and passive calcium ion movement take place via separate channels.

Critical appraisal of oral calcium load test for indirect assessment of intestinal calcium absorption

Two methods of oral calcium load or tolerance test for the indirect assessment of calcium absorption were compared. In 16 patients in whom the diagnosis of absorptive hypercalciuria was made independently, an exaggerated urinary total calcium excretion during four hours following calcium load, indicative of increased calcium absorption according to the method of Pak et al., was found in 15 patients. An abnormally high increment in urinary calcium during third and fourth hours post-calcium load, suggestive of enhanced calcium absorption by the criteria of Broadus et al., was encountered in 14 patients. However, an exaggerated urinary total calcium following calcium load was found in all 7 patients with renal hypercalciuria, whereas only 4 were shown to have an enhanced increment in calcium excretion. It is concluded that both methods are equally reliable in the detection of increased calcium absorption in absorptive hypercalciuria. However, the technique of Broadus et al. is probably superior to that of Pak et al. in the disclosure of increased calcium absorption in renal hypercalciuria.

Action of 1,25-dihydroxyvitamin D3 and a diphosphonate on calcium metabolism in rats.

The effect of 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) on Ca balance, 45Ca kinetics, and bone morphology has been studied in control rats and rats given disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP), 10 mg P/kg sc per day. This large dose of EHDP is known to inhibit bone mineralization and intestinal calcium absorption and to depress the endogenous production of 1,25-(OH)2D3. In conctrol rats, 1,25-(OH)2D3 increased intestinal calcium absorption. However, in contrast to the enhanced calcium absorption that results from an augmentation of dietary calcium, the 1,25(OH)2D3-induced augmentation of calcium absorption does not lead to a rise in calcium retention, the intestinal effect being matched by an increased excretion of urinary calcium. The EHDP-induced decrease of intestinal calcium absorption could be completely prevented by the concomitant administration of 1,25-(OH)2D3 but not the inhibition of bone mineralization. Therefore, in contrast to the impairment of calcium absorption, that of bone mineralization brought about by large doses of EHDP cannot be merely attributed to a decreased production of 1,25-(OH)2D3.

Effect of dietary calcium and age on jejunal calcium absorption in humans studied by intestinal perfusion.

Jejunal calcium absorption was measured from test solutions containing 1.0, 2.5, 5, and 10 mM calcium (as calcium gluconate). Absorption rates increased progressively as luminal calcium concentration was increased, although there was a tendency toward saturation of the absorptive process at the higher concentrations. Calcium absorption was higher in normal young adults than in normal subjects over age 60. In both groups a 300 mg calcium diet for 4-8 wk enhanced calcium absorption relative to absorption rates after 4-8 wk on a 2,000 mg calcium diet. This adaptation was more definite and dramatic in the young than in the old subjects. Indirect estimates suggest that adaptation to a low calcium diet and the higher absorption in young than old normal subjects are mediated by an increased V(max) rather than a decreased K(m).

Lactose and Calcium Metabolism: A Review

Four main hypotheses have been presented in the last four decades to explain the mode of action of lactose on calcium metabolism, but not one of these has been widely accepted. Three of them relate the effect of lactose to enhanced calcium absorption and one to improved calcium deposition in bone. These hypotheses listed in chronological order state that the ingested lactose improves calcium metabolism as a result: A, of providing an acidic pH in the intestinal tract which increases the solubility and the availability of calcium for absorption; B, of chelating calcium in the lumen of the small intestine as a soluble chelate which increases calcium absorption; C, of inhibiting a metabolic system which is responsible for controlling the uptake of divalent cations at the absorption sites in the small intestine and results in an increased calcium absorption; and D, of stimulating certain metabolic steps at the ossification sites which increase the deposition of calcium and improve the efficiency of calcium utilization. Findings by the authors (1,2,3,4,18) agree with hypothesis A and suggest that diet composition affects the mode of action of lactose on calcium absorption. Dietary lactose produced a more acid pH in the intestine, increased calcium retention, raised serum calcium and enhanced bone calcification. The effect on calcium retention and osteogenesis appears to be indirect as lactose-fed rats maintain a relatively younger body composition, i.e., a lower body fat with higher water, protein, ash and calcium, compared to rats receiving no lactose in their diet.

Utilisation of palm, groundnut and melon seed oils by pullets

Synopsis Three oils available locally, palm, groundnut and melon seed, were analysed; melon seed oil was found to contain the highest proportion of unsaturated fatty acids and palm oil was the most saturated. The addition of these oils either at 6 per cent or 10 per cent levels to rations improved egg production by White Plymouth Rock (WPR) pullets but not by Rhode Island Red (RIR) pullets. However, 6 per cent melon seed oil improved the size of eggs laid by RIR. Using 10 per cent melon seed oil in the experimental ration improved egg shell thickness in both breeds. For both breeds 6 per cent groundnut oil depressed calcium absorption, while 6 per cent melon seed oil reduced calcium absorption in only WPR pullets. Addition of 6 per cent and 10 per cent palm oil or 10 per cent of either groundnut oil or melon seed oil enhanced calcium absorption by both breeds. The cholesterol content of egg yolk lipid increased as the degree of unsaturation of the dietary oil increased.

The Effect of Bile Salts on Calcium Absorption

SUMMARY The influence of a series of bile salts on calcium absorption was studied in the goat. Only tauro-cholic acid increased calcium absorption. A bile sequestering agent, cholestyramine, enhanced calcium absorption in the small intestine of the goat and when the same substance was administered orally to cows calcium absorption was improved.

Bile salts and calcium absorption.

1. The study of the effect of bile salts on enhancing calcium absorption in the rachitic chick has been extended to bile salts not present in chick bile, e.g. glycine conjugates and bile alcohol sulphates. 2. Bile and bile salts cause an increase in calcium absorption from sparingly soluble calcium hydrogen phosphate when compared with a suspension of calcium hydrogen phosphate in saline. 3. If the bile ducts of normal rats are tied the absorption of calcium from calcium hydrogen phosphate decreases but can be restored by giving bile salts with the calcium salt. 4. Bile salts increase solubility in water of the sparingly soluble calcium salts, phytate and phosphate at pH values between 6 and 8. 5. Bile salts increase the solubility in lipid solvents of calcium in approximately the same proportion as they increase the absorption of calcium from the gut. 6. The physiological role of bile in calcium absorption and its mode of action are discussed.