Calcium Absorption | Science Based Nutrition

May 20, 2009

[Supplement: Biomarkers of Micronutrient Status: EURRECA Workshop] Existing and potentially novel functional markers of vitamin D status: a systematic review

Filed under: Main Content — Tags: Biomarker, Bmd, Bone Mineral Density, Bone Turnover Markers, Calcium Absorption, Cochrane, Data Extraction, Endpoints, Exclusion Criteria, food, Further Research, Medline, Meta Analysis, Nutrition, Parathyroid, Parathyroid Hormone, Population Subgroups, Quality Assessment, Randomized Controlled Trials, Rct, Rcts, Regression Results, Science, science based nutrition — Seamans, K. M, Cashman, K. D @ 10:00 am

Background: Although serum 25-hydroxyvitamin D [25(OH)D] is the currently accepted vitamin D status marker of choice, use of other biomarkers or functional endpoints have been suggested.

Objective: The objective was to systematically review the effectiveness of 25(OH)D, parathyroid hormone (PTH), bone turnover markers, bone mineral density (BMD), and calcium absorption as biomarkers of vitamin D status.

Design: Methods included a structured search on Ovid MEDLINE, EMBASE (Ovid), and Cochrane CENTRAL; rigorous inclusion/exclusion criteria; data extraction; quality assessment; meta-analysis; and meta-regression.

Results: Thirty-six vitamin D supplementation randomized controlled trials (RCTs) and 4 before-after studies were included. Vitamin D supplementation significantly raised circulating 25(OH)D in all but one RCT, but the response was highly heterogeneous [weighted mean difference (WMD): 34.1 nmol/L; 95% CI: 28.9, 39.2; 32 RCTs; I² = 97%). Vitamin D supplementation (without calcium) significantly lowered circulating PTH (WMD: –0.29 pmol/L; 95% CI: –0.56, –0.02; 11 RCTs; I² = 29%), but this was not apparent in the presence of calcium supplementation. There was a suggestion that whole-body or lumbar spine BMD may be a useful biomarker in older people but not in adolescents. Bone turnover markers were not useful biomarkers of vitamin D status, but 4 before-after studies suggested that intestinal calcium absorption may respond to vitamin D status.

Conclusions: This systematic review confirmed that circulating 25(OH)D is a robust and reliable marker of vitamin D status. Further research is needed to clarify which population subgroups show responses of PTH, BMD, and/or calcium absorption in response to changes in vitamin D status.

Comments (0)

July 1, 1998

Does calcium interfere with iron absorption?

Filed under: Main Content — Tags: Calcium Absorption, Editorials, Hallberg, Iron Absorption — L Hallberg @ 2:00 am

L Hallberg
Jul 1, 1998; 68:3-4
EDITORIALS

Comments (0)

February 7, 2012

[Vitamins, minerals, and phytochemicals] Dietary calcium does not exacerbate phytate inhibition of zinc absorption by women from conventional diets

Filed under: Main Content — Tags: Background, Bioavailability, Calcium Absorption, Conclusions, Conventional Diets, Diet, Dietary Calcium, Factorial Design, High Calcium, Inhibition, Inhibitory Effect, Menus, Objective, Percentage Points, Phytate Content, Rats, Vitamins Minerals, Western Diets, Zinc Absorption, Zn — Science Based Nutrition @ 4:18 pm

Background: Although calcium inhibits zinc bioavailability in rats, especially from high-phytate diets, the effect of calcium on zinc absorption by humans from practical diets remains unclear.

Objective: The objective was to test the inhibitory effect of dietary calcium, in Western diets with high and low phytate content, on zinc absorption.

Design: Using a 2 x 2 factorial design, zinc absorption was determined in 10 healthy women from 1-d diets with moderate and high calcium contents of 700 and 1800 mg/d and low and high phytate contents of 440 and 1800 mg/d. Absorption was measured by using extrinsically added ⁶⁵Zn and subsequent whole-body scintillation counting.

Results: Mean (±SE) fractional zinc absorption was 32.8 ± 2.3% from the moderate-calcium, low-phytate diet; 26.9 ± 2.4% from the moderate-calcium, high-phytate diet; 39.4 ± 2.4% from the high-calcium, low-phytate diet; and 26.2 ± 2.3% from the high-calcium, high-phytate diet. The respective values for absolute zinc absorption were 3.8 ± 0.3, 3.0 ± 0.3, 4.5 ± 0.3, and 3.2 ± 0.3 mg/d. Phytate significantly reduced fractional zinc absorption by 10 percentage points and reduced absolute zinc absorption by 25%, or 1 mg/d. Differences in dietary calcium did not affect zinc absorption, regardless of a high or low dietary phytate content.

Conclusions: In healthy women consuming 1-d menus of ordinary foods (some fortified with calcium), dietary phytate reduces zinc absorption, but calcium does not impair zinc absorption, regardless of whether dietary phytate is low or high.

Comments (0)

[Vitamins, minerals, and phytochemicals] Dietary protein and calcium interact to influence calcium retention: a controlled feeding study

Filed under: Main Content — Tags: Acid Phosphatase, Alkaline Phosphatase, Bone Metabolism, Calcium Absorption, Calcium Balance, Calcium Diet, Calcium Intakes, Calcium Metabolism, Calcium Retention, Clinical Markers, Crossover Design, Deoxypyridinoline, Dietary Calcium, Dietary Protein, High Protein, Insulin Like Growth Factor, Low Calcium, Meat Protein, Term Adaptation, Vitamins Minerals — Science Based Nutrition @ 4:18 pm

Background: The effect of meat protein on calcium retention at different calcium intakes is unresolved.

Objective: The objective was to test the effect of dietary protein on calcium retention at low and high intakes of calcium.

Design: In a randomized controlled feeding study with a 2 x 2 factorial crossover design, healthy postmenopausal women (n = 27) consumed either 675 or 1510 mg Ca/d, with both low and high protein (providing 10% and 20% energy) for 7 wk each, separated by a 3-wk washout period. After 3 wk, the entire diet was extrinsically labeled with ⁴⁷Ca, and isotope retention was monitored by whole-body scintillation counting. Clinical markers of calcium and bone metabolism were measured.

Results: High compared with low dietary protein significantly increased calcium retention from the low-calcium (29.5% compared with 26.0% absorbed) but not the high-calcium diet (18% absorbed). For the low-calcium diet, this effect nearly balanced a protein-related 0.5-mmol/d greater urinary calcium excretion. Protein-related calciuretic effects were independent of dietary calcium. Testing at 1, 2, 3, 5, and 7 wk showed no long-term adaptation in urinary acidity or urinary calcium excretion. High compared with low dietary protein decreased urinary deoxypyridinoline and increased serum insulin-like growth factor I without affecting parathyroid hormone, osteocalcin, bone-specific alkaline phosphatase, or tartrate-resistant acid phosphatase.

Conclusions: In healthy postmenopausal women, a moderate increase in dietary protein, from 10% to 20% of energy, slightly improved calcium absorption from a low-calcium diet, nearly compensating for a slight increase in urinary calcium excretion. Under practical dietary conditions, increased dietary protein from animal sources was not detrimental to calcium balance or short-term indicators of bone health.

Comments (0)

Setting Dietary Reference Intakes with the use of bioavailability data: calcium [Supplement: Micronutrient Bioavailability: Priorities and Challenges for Setting Dietary Reference Values]

Filed under: Main Content — Tags: Calcium Absorption, Calcium Intakes, Dietary Reference Intakes — Abrams, S. A. @ 4:18 pm

The determination of Dietary Reference Intakes (DRIs) for calcium, especially in children, has relied in significant part on the evaluation of the relation between calcium intake and calcium absorption and retention. At present, most of these studies are conducted with the use of dual-tracer stable isotope, although mass balance or other isotope methods are still used occasionally. Studies carried out to evaluate DRI values need to be conducted under the most controlled conditions possible. However, the achievement of such conditions can be difficult, especially in studies in small children, because strict, long-term dietary monitoring and sample collections are not well tolerated. Other dietary factors, which include vitamin D status and the presence of enhancers and inhibitors of calcium absorption, may have to be considered. However, for most healthy populations who do not have very low calcium intakes or serum 25-hydroxyvitamin D concentrations, other dietary factors will not be major determinants of the net calcium absorption or retention that will be used for the establishment of DRI values. Ultimately, DRI values must be chosen based on an attempt to achieve some targeted value for calcium absorption/retention or to maximize, within constraints, the overall calcium absorbed and retained. In children, it is important to use data obtained at the age and pubertal status being evaluated rather than to interpolate from data performed in other age groups.

Comments (0)

Older Posts »