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. AUC9 was 48% greater for calcium citrate malate than for tricalcium phosphate/calcium lactate (P<.001); absorbed calcium calculated from AUC9 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.

Background: Calcium absorption is generally considered to be impaired under conditions of vitamin D deficiency. but the vitamin D status that fully normalizes absorption is not known for humans.Objective: To quantify calcium absorption at two levels of vitamin D repletion. using pharmacokinetic methods and commercially marketed calcium supplements.Design: Two experiment, performed in the spring of the bear. one ear apart. In the first, in which participants were pretreated with 25-hydroxyvitamin D (250HD), mean serum 250HD concentration was 86.5 nmol/L: and in the other with no pretreatment. mean serum concentration was 50.2 nmol/L participants received 500 mg oral calcium loads as a part of a standard low calcium breakfast. A low calcium lunch was provided at mid-day. Blood was obtained fasting and at frequent intervals for 10 to 12 hours thereafterMethods: Relative calcium absorption at the two 250HD concentrations was estimated front the area under the curie (AUC) for the load-induced increment in serum total calcium.Results: AUC(9) (+/- SEM), was 3.63 mg, hr/dL +/- 0.234 in participants pretreated with 250HD and 2.20 +/- 0.240 in those not pretreated (P < 0.001). In briefs absorption was 65%, higher at serum 250HD levels averaging 86.5 nmol/L than at levels averaging 50 nmol/L (both value, within the nominal reference range fur this analyte).Conclusions: Despite the fact that the mean serum 250HD level in the experiment without supplementation,,as within the current reference ranges. calcium absorptive performance at 50 nmol/L was significantly reduced relative to that at a mean 250HD level of 86 nmol/L, Thus. individuals kith serum 25-hydroxyvitamin D levels at the low end of the current reference ranges may not be getting the fall benefit from their calcium intake. We conclude that the lower end of the current reference range is set too low.

Adding three servings of yogurt to the daily diet of older women with habitually low calcium intakes resulted in a significant reduction in urinary excretion of N-telepeptide, a marker for bone resorption. Results were compared to the effects of three servings of a nutrition-poor snack and differences were apparent 7-10 days of starting the diet change. The satiety effect of the snacks resulted in a decrease in intake of other foods. The added nutrients of the yogurt improved overall diet quality substantially, while diet quality declined with the nutrient-poor snack. The results show that diets low in dairy intake are often marginal for several nutrients and that, so far as calcium is concerned, bone makes up for what the diet lacks. Moreover, bone resorption responds rapidly and sensitively to improvements in calcium intake that are readily achievable by an older female population.

When both calcium intake and calcium absorption are measured under controlled conditions, variation in absorption efficiency explains more of the interindividual differences in balance than does actual calcium intake (1). Small wonder, therefore, that interest in measuring absorption has remained high for nearly 40 years. True calcium absorption is defined as the quantitative, unidirectional flux of calcium from intestinal lumen into the blood. It is most accurately measured by a dual-tracer method, with one tracer labeling the oral calcium load and the other labeling the miscible calcium pool into which the absorbed calcium is introduced. This approach was first developed into a practicable human test by deGrazia et al. (2). As described, it is usually time-consuming and expensive. To reduce these barriers for widespread use, Heaney and Recker (3)(4) developed a single-tracer variant for women, requiring only a single blood sample, and calibrated it against a simultaneously performed double-tracer method. The single-tracer method has been used efficiently in thousands of women (5). However, because the calibration is empirical and based on body-size variables, it is not directly suitable for use in men who, with a typically higher proportion of fat-free mass than women, would be expected to distribute absorbed tracer in a larger mass of calcium. To fill this methodologic gap, we performed a small set of parallel measurements in adult men, using the female-based algorithm together wiketh a modified double-tracer approach. Participants in the study were 30 Caucasian men (age range, 20–60 years; weight range, 63.5–104 kg; height range, 1.67–1.93 m). All participants were free of known diseases affecting bone remodeling or calcium homeostasis, and tests were not performed if the individual had experienced any gastrointestinal disturbance in the preceding 5 days. Each gave informed consent after the procedures of the study were explained. Both the project …

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 μg/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.

BACKGROUND Calcium-fortified soy milk is growing in popularity, particularly among vegetarians, but the bioavailability of its calcium was not previously known. Additionally, the validity of isotopic labeling methods for fortified liquid products had not been established. OBJECTIVES The objectives of this study were to compare the bioavailability of the calcium in fortified soy milk with that of calcium in cow milk and to evaluate the method of labeling soy milk for bioavailability testing. DESIGN A within-subject comparison of extrinsically labeled cow milk with intrinsically and extrinsically labeled soy milks was undertaken in 16 healthy men. In all tests, 300-mg Ca loads were given as a part of a light breakfast after an overnight fast. The milks were physically partitioned into liquid and solid phases to enable evaluation of tracer distribution. RESULTS Calcium from intrinsically labeled soy milk was absorbed at only 75% the efficiency of calcium from cow milk. Extrinsic labeling of soy milk did not produce uniform tracer distribution throughout the liquid and solid phases and resulted in a 50% overestimate of true absorbability. CONCLUSION Calcium-fortified soy milk does not constitute a calcium source comparable to cow milk, and extrinsic labeling of such calcium particulate suspensions does not produce the uniform tracer distribution needed for bioavailability testing. Hence, intrinsic labeling of the fortificant is required for such liquid suspensions.

The availability of the calcium contained in a high-calcium mineral water (Sangemini), popular in Italy, was compared in 18 healthy women with the availability of milk calcium ingested at the same calcium load, using45Ca as the tracer in a randomized cross-over design. At an ingested calcium load of 2.5 mmol, absorption fraction averaged 0.433 for milk and 0.475 for Sangemini water. The mean quotient of the two (Sangemini/milk) was 1.129 (±0.056, SEM,P<0.05). The calcium of Sangemini water is thus highly bioavailable, and at least as bioavailable as milk calcium.