Biomedical subjects

C M Weaver

Publications and source records attributed to C M Weaver.

At least 73 records · Page 4Linked to original sources

PubMed1990

Influence of calcium load on absorption fraction.

True calcium absorption was studied as a function of the size of the ingested load in healthy adult women, under meal conditions and at loads ranging from 15 to 500 mg calcium. Fractional absorption was highly inversely correlated with the logarithm of load (P less than 0.001). At the lowest loads, absorption averaged 64.0% and at the highest, 28.6%. The parameters of the best-fit relationship permit reasonably precise calculation of the impact of various calcium dosing and dietary strategies.

Adult↗

PubMed1990

Calcium absorptive consistency.

Calcium absorption efficiency was measured two or three times each in 74 premenopausal and 142 postmenopausal women under conditions predicted to alter absorptive performance. A woman's absorptive consistency was evaluated across differing loads, differing intervals, and substances of differing intrinsic absorbability. In all these circumstances there was a statistically significant correlation between a woman's absorption under differing test situations accounting for up to 60% of the variance typically found in cross-sectional studies. For example, when the same substance but at differing load levels was tested three times over an 8 week period, various coefficients of correlation ranged from +0.773 to +0.849 (P less than 0.001). Even over intervals as long as 5 years correlation of absorption fraction within individuals remained significant (r = +0.487, P less than 0.001).

Adult↗

PubMed1990

Absorbability of calcium sources: the limited role of solubility.

Fractional absorption of seven chemically defined calcium sources was measured in normal adult women under standardized load conditions. Solubility of the sources in water at neutral pH ranged from a low of 0.04 mM to a high of 1500 mM. The relationship of solubility to absorbability was weak. In the range from 0.1 to 10 mM, within which most calcium supplement sources fall, there was no detectable effect of solubility on absorption. Data from four food sources are presented for comparison. Absorbability of food calcium was not clearly related to absorbability of the dominant chemical form in the food concerned. These findings suggests that (1) even under controlled, chemically defined conditions, solubility of a source has very little influence on its absorbability; and (2) absorbability of calcium from food sources is determined mainly by other food components.

Adult↗

PubMed1990

Calcium absorption from kale.

Absorption of calcium from intrinsically labeled kale was measured in 11 normal women and compared in these same subjects with absorption of calcium from labeled milk. The average test load was 300 mg. Fractional calcium absorption from kale averaged 0.409 +/- 0.101 (means +/- SD) and from milk, 0.321 +/- 0.089 (P less than 0.025). In contrast with the poor absorption previously reported for spinach calcium, kale, a low-oxalate vegetable, exhibits excellent absorbability for its calcium.

Adult↗

PubMed1990

Assessing calcium status and metabolism.

Currently, there is no commonly practiced tool for assessing calcium status of individuals or populations. Few biochemical markers reflect calcium status. Fasting urinary calcium:creatinine ratios may hold promise as an easy, inexpensive method to indicate recent calcium status. Calcium status may best be assessed by integrated measures of calcium assimilation, such as total-body calcium. Although bone-mass measurements do not correlate well with recent dietary intakes of calcium, long-term adequacy of calcium intake influences bone mass. Whether low calcium intakes lead to calcium deficiencies depends on one's ability to adapt and conserve calcium. The relationship between calcium status and a particular disease state, such as osteoporosis, hypertension, or colon cancer, cannot be established until a reliable indicator of calcium status is found.

Absorption↗

PubMed1990

Association of magnesium deficiency with the blood pressure-lowering effects of calcium.

The role of dietary calcium and magnesium in the development of hypertension was studied in nine groups, each consisting of nine spontaneously hypertensive rats aged 8-31 weeks. The animals were fed AIN 76A semi-purified diets varying in calcium (0.075, 0.5 and 2.5%) and magnesium (0.01, 0.05 and 0.75%) concentrations according to a 3 x 3 factorial design. Dietary calcium and systolic blood pressure were inversely related, significantly (P less than 0.05) after 12 weeks. Total and ultrafilterable serum calcium concentrations were also significantly negatively correlated with blood pressure (r = -0.46; P = 0.001 and r = -0.57; P = 0.001, respectively). Repeated measures analysis of variance indicated that dietary magnesium had no effect on systolic blood pressure, and no calcium x magnesium interaction on blood pressure was observed. Signs of magnesium deficiency, calcium deposits in the kidneys, and histological lesions were observed in groups on a high-calcium diet receiving normal and low levels of magnesium. Thus a lowering of blood pressure by calcium supplementation, without concomitant magnesium supplementation, was accompanied by biochemical and histological abnormalities in this animal model.

Animals↗

PubMed1990

Agreement between analytical values and label declarations of sodium content of processed packaged foods.

As part of the Food Labeling and Product Surveillance Program of the Food and Drug Administration, samples from 1982, 1984, and 1986 surveys of processed packaged foods (canned, frozen, and dry packaged) were analyzed to determine how closely the foods' actual sodium content matched their label claims for sodium. Samples were classified into three groups: "sodium-free" products (less than 5 mg sodium per serving), and "very-low-sodium" products (5 to 35 mg per serving), and a larger group of products that were labeled as containing more than 35 mg sodium per serving. In the third group, the distribution of actual sodium content fell around 100% of label claims for sodium. For the three survey years, analyzed sodium averaged 101% of label claim (standard deviation [SD] = 25%) for 1982 samples (20 products), 99% of label claim (SD = 28%) for 1984 samples (108 products), and 94% of label claim (SD = 21%) for 1986 samples (265 products). Products labeled "very low sodium" were treated separately because sodium analyses varied widely from the label declarations. However, most "very-low-sodium" products were well under 35 mg sodium per serving. Results indicated that consumers receive reasonably accurate information about the sodium content of processed packaged foods from label claims.

Food Analysis↗

PubMed1989

Oxalate: effect on calcium absorbability.

Absorption of calcium from intrinsically labeled Ca oxalate was measured in 18 normal women and compared with absorption of Ca from milk in these same subjects, both when the test substances were ingested in separate meals and when ingested together. Fractional Ca absorption from oxalate averaged 0.100 +/- 0.043 when ingested alone and 0.140 +/- 0.063 when ingested together with milk. Absorption was, as expected, substantially lower than absorption from milk (0.358 +/- 0.113). Nevertheless Ca oxalate absorbability in these women was higher than we had previously found for spinach Ca. When milk and Ca oxalate were ingested together, there was no interference of oxalate in milk Ca absorption and no evidence of tracer exchange between the two labeled Ca species.

Adult↗

PubMed1989

Congenital hypothyroidism, spiky hair, and cleft palate.

Two brothers are described with athyroidal hypothyroidism, spiky hair, choanal atresia, cleft palate, and bifid epiglottis. Polyhydramnios was present in the third trimester of each pregnancy. These abnormalities appear to represent a new syndrome.

Child, Preschool↗

PubMed1989

Dietary magnesium does not affect blood pressure in spontaneously hypertensive rats.

To determine the therapeutic effectiveness of dietary magnesium in the treatment of established hypertension, 21 male spontaneously hypertensive rats were fed altered levels of magnesium oxide from 17 to 29 weeks of age. The rats were divided into three groups of approximately equal mean baseline systolic blood pressures and fed AIN 76A purified diets containing magnesium at 0.01% (low), 0.05% (normal), and 0.40% (high) levels. Mean systolic blood pressures in the conscious SHR during the 12 week period and terminal direct blood pressures under anesthesia were not significantly different among treatment groups. Total and ultrafilterable serum magnesium concentrations reflected dietary magnesium intake. Total and ultrafilterable serum calcium levels were significantly higher (p less than 0.05) in the low magnesium-fed SHR. Histopathologic alterations indicative of aging did not differ among treatment groups. Therefore, in spite of altered serum mineral status, blood pressure and histopathology were not affected by dietary magnesium.

Animals↗

PubMed1988

Calcium absorbability from spinach.

The absorbability of calcium from spinach was compared with the absorbability of Ca from milk in 13 healthy adults in a randomized cross-over design in which the test meal of either milk or spinach had 200 mg of Ca labeled with 45Ca. Absorption was measured by the standard double-isotope method in which both the test food and the miscible Ca pool are labeled with different Ca tracers. Measurement of both Ca and oxalate in our test spinach revealed a very slight stoichiometric excess of oxalate; hence it is likely that all of the spinach Ca was effectively bound. Absorption was higher from milk in every case, with the mean absorption from milk averaging 27.6% and from spinach, 5.1%. The mean within-subject difference between Ca absorption from milk and from spinach was 22.5 +/- 9.5% (P less than 0.0001). These results conclusively establish that spinach Ca is much less readily available than milk Ca.

Adult↗

PubMed1987

Oxalic acid decreases calcium absorption in rats.

Calcium absorption from salts and foods intrinsically labeled with 45Ca was determined in the rat model. Calcium bioavailability was nearly 10 times greater for low oxalate kale, CaCO3 and CaCl2 than from CaC2O4 (calcium oxalate) and spinach (high in oxalates). Extrinsic and intrinsic labeling techniques gave a similar assessment of calcium bioavailability from kale but not from spinach.

Absorption↗

PubMed1986

The response to L-carnitine and glycine therapy in isovaleric acidaemia.

The profound metabolic disturbances which occur in isovaleric acidaemia are due to the intramitochondrial accumulation of isovaleryl coenzyme A (CoA) with a consequent reduction in the availability of free CoA. Secondary carnitine insufficiency is also a feature of this and other disorders of organic acid metabolism. A patient who presented at 2.5 years of age was diagnosed using capillary GC-MS as having isovaleric acidaemia. She showed the full spectrum of abnormal organic acids previously associated with the 'neonatal' form of the disease despite her late presentation, indicating that it is inappropriate to refer to acute early and late onset forms of isovaleric acidaemia. Instead, a spectrum of disease exists, determined by environmental factors, residual enzyme activities and modifying effects of different phenotypes in different individuals. She also showed evidence of carnitine insufficiency. An oral challenge with L-carnitine resulted in the excretion of large amounts of urinary acylcarnitines which were shown by use of fast atom bombardment mass spectrometry to be primarily isovalerylcarnitine. Regular glycine supplementation caused no significant increase in urinary isovalerylglycine and had to be stopped because of side-effects after 5 days. An oral L-carnitine challenge during glycine supplementation resulted in a marked increase in isovalerylglycine excretion, again associated with the excretion of large amounts of isovalerylcarnitine. Carnitine acts by removing (detoxifying) intramitochondrial isovaleryl groups and, in the presence of glycine, it promotes the formation of isovalerylglycine. We believe L-carnitine supplementation is of value in the treatment of isovaleric acidaemia and that, in the present case, L-carnitine together with a moderate dietary restriction has proved to be the optimum form of therapy.

Amino Acid Metabolism, Inborn Errors↗

PubMed1986

Metabolism in rats of selenium from intrinsically and extrinsically labeled isolated soy protein.

Absorption, retention and tissue accumulation by rats of 75Se from intrinsically labeled isolated soy protein were compared with utilization of 75Se from the extrinsic sources of [75Se]selenite, [75Se]selenate or [75Se]selenomethionine. Extrinsic sources of selenium were given by gavage or mixed with isolated soy protein. There were no differences in absorption and retention of 75Se from intrinsically labeled soy diet compared to the three extrinsically labeled soy diets. Of the three extrinsic sources tested, 75Se from selenate was better absorbed than from selenite or selenomethionine when incorporated into a soy diet. Absorption of 75Se was significantly lower when given to animals in gavage solution than when mixed with soy diets. After a 14-d test period, retention of 75Se was the same for all four soy diet groups. In gavaged groups, 75Se from selenomethionine was retained to a greater extent than 75Se from selenite. The liver, testes and kidney accumulated more 75Se from the test meal than did the blood and lungs. In the testes more 75Se from selenite and selenate was accumulated than from selenomethionine-labeled diets. Selenium absorption from the soy isolate source was very high (86-96%), indicating that, although soy does not normally contain high levels of selenium, the selenium present is well absorbed from this plant source.

Animals↗

PubMed1986

Bioavailability of zinc to rats as affected by protein source and previous dietary intake.

The bioavailability of zinc from defatted soy flour, dried chicken meat or mixed (50:50 dry weight basis) soy flour and chicken meat included in egg white-based diets was investigated in rats. Following a 6-d experimental diet (9 ppm Zn) feeding period, marginally zinc-depleted weanling rats were fed a test meal, identical in composition to the experimental diet except that the protein source was labeled either intrinsically or extrinsically with 65Zn. Retention of 65Zn from the chicken test meal was significantly higher than that from the soy test meal. Retention of 65Zn from the mixed soy/chicken test meal was midway between the retention values for either protein alone regardless of which protein source was labeled. Intrinsic and extrinsic labeling techniques resulted in similar assessment of zinc bioavailability. Additionally, the influence of previous dietary protein source on zinc retention from a soy test meal was investigated. Retention of 65Zn from an intrinsically labeled soy test meal was higher in rats adapted to chicken protein than in rats adapted to soy protein. The levels of tibia zinc and tibia 65Zn were associated with whole-body retention of 65Zn.

Animals↗

PubMed1985

Intrinsic mineral labeling of edible plants: methods and uses.

The fate of minerals can be conveniently studied through intrinsic labeling techniques. The mineral of interest is biologically incorporated into the food in a form that can be distinguished analytically from the natural form of the element. Radiolabels have traditionally been used to study such problems as the uptake of minerals by plants, the gross and subcellular mineral distribution in plant tissues, the form and associations of the deposited mineral, and the bioavailability of minerals to animals and humans. The use of stable (nonradioactive) isotopes as a label offers the potential of safely studying bioavailability of minerals from individual foods in human population groups of all ages using foods processed in normal food handling and processing facilities.

Agriculture↗

PubMed1984

Bioavailability of zinc to rats from defatted soy flour, acid-precipitated soy concentrate and neutralized soy concentrate as determined by intrinsic and extrinsic labeling techniques.

The bioavailability of 65Zn from intrinsically and extrinsically labeled soy flour, acid-precipitated soy concentrate and neutralized soy concentrate was evaluated in rats. Weanling rats were fed marginally zinc-deficient diets, providing 8 ppm zinc from one of these three soy products, for 7 days. The rats then received a radioactively labeled test meal, identical in composition to the previous diet except that the soy product was either intrinsically or extrinsically labeled with 65Zn. After the test meal the rats were again fed diets the same as those consumed prior to the test meal. Whole-body retention of 65Zn at 24 hours and 12 days as well as 65Zn retained in tibias of rats given meals containing neutralized concentrate-based meals was significantly lower than for rats given meals containing the soy flour or acid-precipitated concentrate. In addition, retention of 65Zn from the extrinsically labeled acid-precipitated concentrate-based meal was significantly higher than from the same product intrinsically labeled. These findings confirm the results of previous feeding studies from which it was suggested that neutralization of soy protein concentrates reduces zinc bioavailability to the rat. In addition, the results are taken to suggest that experimental conditions may influence the validity of the extrinsic labeling technique for zinc.

Animals↗

PubMed1984

Radiolabeled iron in soybeans: intrinsic labeling and bioavailability of iron to rats from defatted flour.

Soybeans can be efficiently labeled with radiolabeled iron by supplying the iron via a nutrient culture medium as an iron salt or as a chelate. By using dual labeled iron and EDTA, it was determined that none of the chelator was transported to the shoots with the iron. Therefore, the use of chelated iron as the iron source in the nutrient medium should not affect assessments of bioavailability of iron from plants. Bioavailability (determined from whole-body retention curves of 59Fe in rats) of iron from defatted soy flour was relatively high and addition of vitamin C did not significantly enhance absorption of iron from defatted soy flour.

Animals↗