Biomedical subjects

M Susan Dowell

Publications and source records attributed to M Susan Dowell.

3 recordsLinked 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↗

PubMed2003

Calcium absorption varies within the reference range for serum 25-hydroxyvitamin D.

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 experiments performed in the spring of the year, one year apart. In the first, in which participants were pretreated with 25-hydroxyvitamin D (25OHD), mean serum 25OHD 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 thereafter. METHODS: Relative calcium absorption at the two 25OHD concentrations was estimated from the area under the curve (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 25OHD and 2.20 +/- 0.240 in those not pretreated (P < 0.001). In brief, absorption was 65% higher at serum 25OHD levels averaging 86.5 nmol/L than at levels averaging 50 nmol/L (both values within the nominal reference range for this analyte). CONCLUSIONS: Despite the fact that the mean serum 25OHD level in the experiment without supplementation was within the current reference ranges, calcium absorptive performance at 50 nmol/L was significantly reduced relative to that at a mean 25OHD level of 86 nmol/L. Thus, individuals with serum 25-hydroxyvitamin D levels at the low end of the current reference ranges may not be getting the full benefit from their calcium intake. We conclude that the lower end of the current reference range is set too low.

Area Under Curve↗

PubMed2002

Effect of yogurt on a urinary marker of bone resorption in postmenopausal women.

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.

Bone Resorption↗