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At least 145 records · Page 8Linked to original sources
PubMed2005

Calcium fortification systems differ in bioavailability.

The objective of this study was to compare the bioavailability of calcium from two fortification systems used in orange juice. The design was randomized crossover, within-subject. The subjects were 25 healthy premenopausal women in an academic health sciences center. Two commercially marketed calcium-fortified orange juices, ingested in an amount providing 500 mg calcium, were taken at breakfast after an overnight fast. The two fortification systems tested were calcium citrate malate and a combination of tricalcium phosphate and calcium lactate (tricalcium phosphate/calcium lactate). The main outcome measure was the area under the curve (AUC) for the increase in serum calcium from 0 to 9 hours after ingesting the test calcium source. Statistical analyses performed were repeated measures analysis of variance, testing source, and sequence. AUC 9 was 48% greater for calcium citrate malate than for tricalcium phosphate/calcium lactate ( P < .001); absorbed calcium calculated from AUC 9 values (mean+/-standard error of the mean) was 148+/-9.0 mg and 100+/-8.9 mg for calcium citrate malate and tricalcium phosphate/calcium lactate, respectively. The results indicate that equivalent calcium contents on a nutritional label do not guarantee equivalent nutritional value. Nutritionists and dietetics professionals should encourage manufacturers of fortified products to provide information on bioavailability.

Adult↗
PubMed1994

Cica clamp evaluation of parathyroid responsiveness in chronic hypoparathyroidism: a sequential citrate and calcium clamp study.

The objective of this study was to examine if the Cica clamp technique, sequential citrate and calcium administration sufficient to promote steady-state-blood-ionized calcium concentrations (B-Ca2+) of about 0.20 mmol/l below and above the individual baseline concentrations, was able to produce reciprocal changes in serum intact parathyroid hormone [S-PTH(1-84)] in chronic surgical hypoparathyroidism (HP; n = 10) and chronic idiopathic HP (n = 2). The calcium set point according to Brown [J Clin Endocrinol Metab 1993;56:572-581] was calculated when possible. Data from 22 controls were included for comparison. Within 5-10 min B-Ca2+ lowering in responding patients with surgical HP (n = 7) and controls demonstrated transient S-PTH(1-84) peaks from 1.3 +/- 0.7 to 3.5 +/- 3.2 pmol/l (p < 0.05) and from 3.4 +/- 1.2 to 19.1 +/- 6.7 pmol/l (p < 0.001), respectively. Subsequently S-PTH(1-84) declined to steady-state hypersecretion levels of about 1.9 +/- 1.2 and 8.6 +/- 2.6 pmol/l, respectively. An increase of B-Ca2+ made S-PTH(1-84) unmeasurable in all HP responders except one, while S-PTH(1-84) remained measurable, 0.9 +/- 0.4 pmol/l, in all controls. In responding patients with surgical HP and controls the respective calcium set points averaged 1.05 +/- 0.06 and 1.13 +/- 0.04 mmol/l, respectively (p < 0.001). The remaining nonresponders with surgical and idiopathic HP did not respond at all. To summarize, 7 out of 10 patients with surgical HP demonstrated a normal pattern of parathyroid response to sequential B-Ca2+ decreases and increases.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Gastric acidity, atrophic gastritis, and calcium absorption.

The deleterious effects of increased gastric pH on calcium absorption from calcium carbonate supplements were observed about 25 years ago. Increasing use of calcium supplements, especially by the elderly, has raised questions about bioavailability from various calcium sources. Decreased gastric acidity is common in the elderly and in patients taking antiulcer medications. A critical review of the available human studies that have investigated the role of gastric acidity in calcium bioavailability suggests that the effects of increased gastric pH are only apparent when poorly soluble calcium salts are taken after an overnight fast. Soluble calcium sources, such as calcium citrate and calcium from milk, are absorbed normally in elderly subjects with atrophic gastritis. Moreover, calcium carbonate, a relatively insoluble calcium salt, is well absorbed in atrophic gastritis patients if administered with a meal. In order to maximize calcium bioavailability, elderly subjects should increase their calcium intakes to at least recommended levels, preferably by increasing milk consumption. When calcium supplements are used to augment dietary calcium sources, a highly soluble source should be of benefit or calcium carbonate may be taken with a meal.

Absorption↗
PubMedDate not supplied

Osteomalacia secondary to renal tubular acidosis in a patient with primary Sjögren's syndrome.

We report a case of a 41-year-old woman whose disease manifested as osteomalacia and whose etiological investigation revealed renal tubular acidosis secondary to primary Sjögren's syndrome. Proximal tubular dysfunction was also present and was documented by increased urinary excretion of beta-2-microglobulin and retinol-binding protein. The patient showed clinical and laboratory improvement after treatment with oral potassium citrate, calcium supplements and steroids.

Acidosis, Renal Tubular↗
PubMed1989

[Reduction of urinary oxalate excretion by administration of calcium and citrate].

Oxalic acid seems to be more important for the formation of calcium oxalate stone than calcium. Three grams of calcium lactate and 3 g of uraly U were administered to 35 urolithiasis patients, whose stones were mainly composed of calcium oxalate. Urinary oxalate level was reduced significantly without raising urinary calcium level by the administration of the two drugs for two weeks. The reduction of oxalic acid was particularly remarkable in patients without hypercalciuria. The mechanism of action of these drugs and the relation to dietary management were discussed.

Adult↗
PubMed1983

Raising urinary citrate lowers calcium oxalate and calcium phosphate crystal formation in whole urine.

Crystal formation in whole urine was studied by the technique of rapid evaporation to 1,250 mosmol/l with and without raising citrate concentration by 40-50%. The added citrate reduced calcium oxalate crystal formation at pH 5.3 by about 25% and reduced calcium phosphate crystal formation at pH 6.8 by some 42%. These results support the view that citrate is important in maintaining calcium in solution in whole urine, and that raising the urinary citrate could be effective treatment for calcium oxalate/phosphate urolithiasis.

Calcium Oxalate↗
PubMed1994

Urinary acidification and urinary excretion of calcium and citrate in women with bilateral medullary sponge kidney.

Urinary acidification ability, acid-base status and urinary excretion of calcium and citrate were evaluated in 10 women with bilateral medullary sponge kidney (MSK) and in 10 healthy women. Patients with MSK had higher fasting urine pH compared to normal controls (p < 0.01). Four patients had incomplete renal tubular acidiosis (iRTA), 3 had hypercalciuria, and 5 patients had hypocitraturia. The 24-hour urinary excretion of calcium was increased in the females with MSK (5.23 +/- 0.78 mmol) compared to the healthy females (3.49 +/- 0.29 mmol) (p < 0.02), and increased in MSK patients with iRTA (7.32 +/- 1.45 mmol) compared to patients with normal urinary acidification (3.83 +/- 0.12 mmol) (p < 0.01). The patients with iRTA had reduced levels of plasma standard bicarbonate (20.5 +/- 1.0) after fasting compared to patients with normal urinary acidification (23.8 +/- 0.8) and healthy women (22.7 +/- 0.6) (p < 0.01), and reduced levels of 24-hour urinary excretion of citrate (0.93 +/- 0.25 mmol) compared to patients with normal urinary acidification (3.58 +/- 0.51) and healthy women (2.78 +/- 0.49) (p < 0.005). A positive correlation was found between the degree of acidosis during ammonium chloride loading and urinary excretion of calcium (r = 0.71, p = 0.02), and a negative correlation between the degree of acidosis during ammonium chloride loading and urinary citrate excretion (r = 0.87, p = 0.001). The results suggest that defective urinary acidification might play an important role in the mechanism of hypercalciuria and hypocitraturia in patients with medullary sponge kidney.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis, Renal Tubular↗
PubMed1990

On the relation between citrate and calcium in normal and stone-former subjects.

The aim of this work is to evaluate citrate in a group of patients with calcium oxalate urolithiasis and in a control group for detecting possible differences between the two groups. The mean urinary concentration in the stone-formers was found significantly lower than in the controls. Particularly interesting was the correlation study between citrate and calcium. It was found that patients with hypocitraturia have hypercalciuria. Thus, it is particularly interesting to point out the importance of citrate in preventing the risk of lithiasis in the group of stone-formers studied by us.

Adult↗
PubMed1994

Risk factors for low urinary citrate in calcium nephrolithiasis: low vegetable fibre intake and low urine volume to be added to the list.

Risk factors for low urinary citrate excretion were assessed in 34 consecutive male recurrent idiopathic calcium stone formers (RCSF) who collected two 24-h urines while on free-choice diet. Overt hypocitraturia (hypo-cit) was defined as UCit x V < 1.70 mmol/day, and 'low' citraturia (low-cit) as UCit x V between 1.70 and 2.11 mmol/day. Twenty-three RCSF had normocitraturia (normo-cit), six low-cit and five hypo-cit. UCit x V positively correlated with urine volume (VOLUME, r = 0.44, P = 0.009), vegetable fibre intake (fibers, r = 0.46, P = 0.009) and GI-alkali absorption (alkali, r = 0.47, P = 0.006), and volume, fibres and alkali tended to be lower among RCSF with low-/hypo-cit. A 3-day NH4Cl loading test (0.95 mEq/kg BW daily in 3 doses) was performed in RCSF as well as in 14 age-matched healthy male controls (C). On a plot of urine pH versus serum bicarbonate, 10 of 11 RCSF with low-/hypo-cit, but only six of 23 with normo-cit (P = 0.0004) fell off the normal range, indicating incomplete RTA. Two or more risk factors simultaneously occurred in only four of 23 RCSF with normo-cit, but in eight of 11 with low-/hypo-cit (P = 0.002). In conclusion, incomplete RTA is the most prevalent risk factor for low-/hypo-cit in RCSF, and decreases in vegetable fibres and urine volume emerge as two new risk factors for low urinary CIT.

Acidosis, Renal Tubular↗
PubMed1963

EFFECT OF ACETAZOLAMIDE AND TRIPLE SULFONAMIDE ON CITRATE AND CALCIUM EXCRETION.

The administration of acetazolamide was shown to increase the excretion of calcium in both normal persons and in stone formers, while at the same time the urinary excretion of citrate was reduced. Urinary citrate is potentially of importance in chelating calcium and preventing it from precipitating. In view of the chemical similarity between acetazolamide and the sulfonamides it was considered that the latter might produce a similar effect, with potential hazard if administered to a stone former. This was shown not to be the case.

Acetazolamide↗
PubMed1994

Slow-release sodium fluoride in the management of postmenopausal osteoporosis. A randomized controlled trial.

OBJECTIVE: To test whether intermittent treatment with slow-release sodium fluoride and continuous calcium citrate supplementation inhibits vertebral fractures without causing fluoride complications. DESIGN: A placebo-controlled, randomized trial. SETTING: Outpatient setting of specialty clinics in Dallas and Temple, Texas. INTERVENTIONS: Slow-release sodium fluoride (25 mg twice daily) in repeated 14-month cycles (12 months on treatment followed by 2 months off treatment) compared with placebo. Both groups took calcium citrate (400 mg calcium twice daily) continuously. PATIENTS: 110 patients with postmenopausal osteoporosis were randomly assigned to two groups. In the slow-release sodium fluoride group, 48 of 54 patients completed more than 1 cycle of treatment (mean, 2.44 cycles/patient), whereas 51 of 56 patients in the placebo group completed at least 1 cycle (mean, 2.14 cycles/patient) in this interim analysis. MEASUREMENTS: Vertebral fracture rate and lumbar bone mineral content. Vertebral fractures were quantified from yearly radiographs. Bone mass was determined annually by densitometry. RESULTS: In the sodium fluoride group, the mean L2 to L4 bone mineral content increased by 4% to 6% in each cycle and the mean femoral neck bone density increased by 4.1% and 2.1% during the first two cycles, but the radial bone density did not change. The placebo group showed no statistical change in bone mass at any site. Compared with the placebo group, the sodium fluoride group had a lower individual new vertebral fracture rate (0.057/patient cycle compared with 0.204/patient cycle, P = 0.017), a higher fracture-free rate (83.3% compared with 64.7%, P = 0.042), and a lower group fracture rate (0.085/patient cycle compared with 0.239/patient cycle, P = 0.006). The side-effect profile was similar for the two groups; no patient developed microfractures, hip fractures, or blood loss anemia. CONCLUSIONS: Intermittent slow-release sodium fluoride plus continuous calcium citrate, administered for about 2.5 years, inhibits new vertebral fractures, increases the mean spinal bone mass without decreasing the radial shaft bone density, and is safe to use.

Aged↗
PubMed1989

On the relation between citrate and calcium in normal and stone-former subjects.

The aim of this work is to evaluate citrate in a group of patients with calcium oxalate urolithiasis and in a control group for detecting possible differences between the two groups. The mean urinary concentration in groups of stone-formers was found significantly lower than in the control group. Particularly interesting was the correlation study between citrate and calcium. It was found that patients with hypocitraturia have hypercalciuria. Thus, it is particularly interesting to point out the importance of citrate in preventing the risk of lithiasis in stone-formers studied by us.

Adult↗
PubMed2001

Absorbability and cost effectiveness in calcium supplementation.

BACKGROUND: Cost-effectiveness of calcium supplementation depends not only on the cost of the product but on the efficiency of its absorption. Published cost-benefit analyses assume equal bioavailability for all calcium sources. Some published studies have suggested that there are differences in both the bioavailability and cost of the major calcium supplements. DESIGN: Randomized four period, three-way cross-over comparing single doses of off-the-shelf commercial calcium supplements containing either calcium carbonate or calcium citrate compared with a no-load blank and with encapsulated calcium carbonate devoid of other ingredients; subjects rendered fully vitamin D-replete with 10 microg/day 25(OH)D by mouth, starting one week prior to the first test. SUBJECTS: 24 postmenopausal women METHODS: Pharmacokinetic analysis of the increment in serum total and ionized calcium and the decrement in serum iPTH induced by an oral calcium load, based upon multiple blood samples over a 24-hour period; measurement of the rise in urine calcium excretion. Data analyzed by repeated measures ANOVA. Cost calculations based on average retail prices of marketed products used in this study from April through October, 2000. RESULTS: All three calcium sources (marketed calcium carbonate, encapsulated calcium carbonate and marketed calcium citrate) produced identical 24-hour time courses for the increment in total serum calcium. Thus, these were equally absorbed and had equivalent bioavailability. Urine calcium rose slightly more with the citrate than with the carbonate preparations. but the difference was not significant. Serum iPTH showed the expected depression accompanying the rise in serum calcium, and there were no significant differences between products. CONCLUSION: Given the equivalent bioavailability of the two marketed products, the cost benefit analysis favors the less expensive carbonate product.

Area Under Curve↗