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S R Lynch

Publications and source records attributed to S R Lynch.

At least 37 records · Page 2Linked to original sources
PubMed1991

Assessment of the role of nonheme-iron availability in iron balance.

To assess the nutritional relevance of absorption studies that use extrinsically labeled single meals, we developed a method for measuring nonheme-iron absorption from the diet and compared the results with absorption from single meals. When subjects consumed their usual diet, there was good agreement between dietary absorption (6.4%) and representative single meals fed in the laboratory (6.1%). Nonheme-iron availability, as estimated by a model that incorporated the effect of both enhancers and inhibitors, correlated significantly with absorption from single meals but not with dietary absorption. When the diet was modified to promote iron absorption maximally, dietary absorption increased only slightly (8.0%) and remained significantly lower than it was from single meals (13.5%). With an inhibitory diet, the decrease in absorption from single meals was similarly exaggerated. These results indicate that in the context of a varied Western diet, nonheme-iron bioavailability is less important than absorption studies with single meals would suggest.

Absorption↗
PubMed1989

Food iron absorption in idiopathic hemochromatosis.

The relationship between iron status and food iron absorption was evaluated in 75 normal volunteers, 15 patients with idiopathic hemochromatosis, and 22 heterozygotes by using double extrinsic radioiron tags to label independently the nonheme and heme iron components of a hamburger meal. In normal subjects, absorption from each of these pools was inversely correlated with storage iron, as measured by the serum ferritin concentration. In patients with hemochromatosis, absorption of both forms of iron was far greater than would be predicted from the relationship between absorption and serum ferritin observed in normal volunteers. Nevertheless, there was still a modest but statistically significant reduction in absorption of nonheme iron with increasing serum ferritin. This relationship could not be demonstrated in the case of heme iron absorption. In heterozygotes, nonheme iron absorption from a hamburger meal containing no supplementary iron did not differ significantly from that observed in normal volunteers. However, when this meal was both modified to promote bioavailability and supplemented with iron, absorption of nonheme iron was significantly elevated. These studies confirm the presence of excessive nonheme iron absorption even from unfortified meals in patients with idiopathic hemochromatosis and suggest in addition that they are particularly susceptible to iron loading from diets containing a high proportion of heme iron. Impaired regulation of nonheme iron absorption was also observed in heterozygous individuals, but a statistically significant abnormality was demonstrable only when the test meal contained a large highly bioavailable iron supplement.

Adult↗
PubMed1989

Iron absorption in humans as influenced by bovine milk proteins.

The effect of the two major bovine milk protein fractions on the dialyzability of iron in vitro under simulated gastrointestinal conditions and on the absorption of Fe by humans was studied. Liquid-formula meals were prepared from hydrolyzed maize starch, corn oil, and either spray-dried egg white or a milk-protein product. In meals containing egg white, 3.32% of the Fe was dialyzable. The substitution of casein and whey protein products reduced the dialyzable fraction to 0.19-0.56% and 0.86-1.60%, respectively. Percentage Fe absorption was also reduced by the substitution of casein or whey protein for egg white. Mean absorption values fell from 6.67 to 3.65% and 2.53 to 0.98%, respectively. When the intact milk-protein products were replaced by enzyme- or acid-hydrolyzed preparations, the dialyzable fraction increased markedly and in proportion to the extent of hydrolysis. A similar but much smaller effect on absorption was observed. These studies suggest that bovine casein and whey proteins are responsible at least in part for the poor bioavailability of the Fe in some infant formulas.

Adult↗
PubMed1989

Iron fortification of infant cereals: a proposal for the use of ferrous fumarate or ferrous succinate.

Hemoglobin-repletion tests in rats, organoleptic studies, and iron-absorption studies in humans were used to search for Fe sources with high bioavailability that could be added to infant cereals as alternatives to the Fe compounds currently used for fortification. From rat and organoleptic studies on 11 alternative Fe sources, ferrous fumarate, ferrous succinate, and ferric saccharate were selected as the most suitable for infant-cereal fortification and, by use of radioactive labels, absorption of those compounds from fortified cereal was measured in adult human volunteers. There was no difference in absorption between ferrous fumarate and ferrous sulfate whereas the values for ferrous succinate, ferrous saccharate (10% Fe), and ferric pyrophosphate were 92%, 74%, and 39% of the ferrous sulfate values, respectively. We conclude that ferrous fumarate and ferrous succinate are highly available Fe sources in man that can be used to fortify infant cereals without causing fat oxidation or discoloration.

Absorption↗
PubMed1989

Duodenal iron proteins in idiopathic hemochromatosis.

This study was undertaken to assess the relationship between iron absorption and the concentration of duodenal iron proteins in normal subjects and patients with idiopathic hemochromatosis (IH). Biopsies were obtained endoscopically from the duodenum in 17 normal subjects, 3 of whom were mildly iron deficient, and 7 patients with untreated IH. The absorption of both heme and nonheme iron was increased in IH despite a 20-fold elevation in serum ferritin. Immunoassays using MAb were used to measure transferrin, H-rich ferritin, and L-rich ferritin in mucosal samples. Mucosal transferrin concentrations in normal subjects did not correlate with either iron status or iron absorption, indicating that mucosal transferrin plays no physiological role in iron absorption. Mucosal transferrin was significantly lower in IH, presumably because of a decrease in mucosal transferrin receptors. Mucosal H and L ferritin concentrations were directly related to body iron stores and inversely related to iron absorption in normal subjects. In IH, mucosal H and L ferritin failed to increase in parallel with the serum ferritin, but were appropriate for the level of iron absorption. The relationship of mucosal H/L ferritin in IH did not differ from that observed in normal subjects. Our findings indicate that the major abnormality in duodenal iron proteins in IH is a parallel decrease in the concentration of H- and L-rich ferritin. It is not evident whether this is the result or the cause of the absorptive abnormality.

Adult↗
PubMed1988

Iron absorption from fortified flat breads.

1. Radio-iron absorption measurements were performed in healthy volunteer subjects to assess the availability of fortification Fe added to various bread products. 2. When ferrous sulphate was used as a fortifier, Fe absorption from a traditional Egyptian flat bread (Baladi) averaged only 16% of that observed with European bread. This difference was attributed to the high extraction flour used to prepare Baladi bread. 3. The inhibiting effect of Baladi bread was largely eliminated by adding EDTA to the flour before baking.

Adult↗
PubMed1988

Iron absorption in humans: bovine serum albumin compared with beef muscle and egg white.

We studied the influence of bovine serum albumin and beef meat on nonheme iron absorption in humans and on dialyzable iron in vitro. The addition of serum albumin to a maize gruel had no significant effect on nonheme Fe absorption whereas the addition of beef meat caused a threefold increase. When added to a bread meal, serum albumin caused a modest 60% increase in nonheme Fe absorption and beef meat had no effect. When added to a protein-free meal, serum albumin reduced Fe absorption by 47% compared with a 72% reduction on addition of egg white. The bioavailability of nonheme Fe from meals containing serum albumin was consistently overestimated by the in vitro technique. We conclude that the facilitation of nonheme Fe absorption by meat is not a general property of all animal protein but is better explained by the action of one or more specific animal tissues.

Adult↗
PubMed1987

Use of capillary blood for the evaluation of iron status.

The accuracy and precision of measurements of iron status made on the capillary blood from a single 75 X 1-mm microhematocrit tube were evaluated in 301 normal volunteers. After recording the hematocrit value, a hematofluorometer was used to assay erythrocyte protoporphyrin directly on the packed red cell fraction. Values in the low normal range were 50-100% higher than assays by an extraction technique in simultaneously collected venous blood. However, measurements in the iron deficient range were only 12% greater. Plasma ferritin concentration was determined by using an enzyme-linked immunoassay on 10-microliters plasma retrieved after measuring the hematocrit. Capillary values were approximately 7% higher than venous concentrations, the proportional difference being consistent throughout the measured range. When the individual measurements were combined to calculate the iron storage status of each individual, the frequency distribution of iron stores in 141 female volunteers between 18 and 36 years of age was approximately Gaussian and paralleled that calculated for women aged 18-44 years in NHANES II. These studies demonstrate that iron status can be determined accurately from the measurement of hematocrit, erythrocyte protoporphyrin, and ferritin on a single microhematocrit tube of capillary blood.

Adolescent↗
PubMed1986

The liabilities of iron deficiency.

Iron has been recognized as a potent hematinic since the inception of hematology as a clinical discipline. Even ancient civilizations believed in the beneficial effects of medicinal iron. Nevertheless, the precise functional liabilities of iron lack remain the subject of continuing debate. The consequences of iron deficiency, particularly from a socioeconomic standpoint, are especially important in light of its high global prevalence. A recent review of the literature indicates that approximately 30% of the estimated world population of nearly 4.5 billion are anemic, and at least half of these, 500 to 600 million people, are believed to have iron deficiency anemia.

Adult↗
PubMed1986

Estimates of iron sufficiency in the US population.

Traditionally the iron status of a population is assessed by estimating the prevalence of iron deficiency anemia. This approach is inadequate in countries where the diet is heavily fortified with iron because it conveys no information about the iron-replete segment of the population. In the present study iron status of a US adult population was evaluated using data collected in the second National Health and Nutrition Examination Survey (NHANES II). Body iron was estimated in each of 2,829 individuals from measurements of hemoglobin concentration, serum ferritin, transferrin saturation, and erythrocyte protoporphyrin. When individuals between 18 and 64 years of age were divided on the basis of sex and menstrual status, body iron reserves were normally distributed and averaged 309 mg in women 18 to 44 years, 608 mg in women 45 to 64 years, and 776 mg in men 18 to 64 years. The dispersion of storage iron in these groups was similar, with standard deviations of 346, 372, and 313 mg, respectively. The prevalence of iron deficiency anemia was surprisingly low, ranging from only 0.2% in adult men to 2.6% and 1.9% in pre- and postmenopausal women, respectively. Epidemiologic methods that examine iron status in the entire population assume importance in light of evidence that in certain segments of the US population, iron deficiency anemia is now less common than the homozygous state for hereditary hemochromatosis.

Adult↗
PubMed1985

Soy protein products and heme iron absorption in humans.

Dual radioiron tags were used to measure both heme and nonheme iron absorption simultaneously from meat-containing meals in 76 healthy male volunteers. Partial substitution of beef with soy flour reduced the availability of nonheme iron but improved the percentage absorption of heme iron significantly (27 to 59% rise). In contradistinction three other powerful inhibitors of nonheme iron absorption, bran, tea, and desferrioxamine, had no appreciable effect on heme. Ascorbic acid (100 mg and 1000 mg in separate experiments) improved nonheme iron uptake markedly but also failed to alter the assimilation of heme. These studies demonstrate that the deleterious effects on iron nutrition of substituting soy protein for beef are partially offset by improved availability of the remaining heme iron as well as by an increase in the nonheme iron content of the meal.

Adolescent↗
PubMed1984

Iron absorption from legumes in humans.

Iron bioavailability in a variety of legumes was determined by radioisotopic measurements of iron absorption in human subjects. Soybeans, black beans, lentils, mung beans, and split peas were prepared as soups, labeled by the extrinsic tag method, and served to fasting subjects. Mean percentage absorption was uniformly low, ranging from 0.84 to 1.91%. Differences in absorption between the means were not statistically significant. The results indicate that these five commonly eaten legumes are all poor sources of dietary iron.

Absorption↗
PubMed1983

Malignant lymphocytic lymphoma. Demonstration of a serum inhibitor of myelopoiesis and response to combination chemotherapy.

A case of diffuse well differentiated lymphocytic lymphoma with associated leukopenia, is described. The colony-forming unit (CFU-C) assay was used to quantitate myeloid precursor cells and to test for the presence of suppressor cells and/or serum factors inhibiting myeloid cell proliferation. Mild suppression of CFU-C was noted with the patient's bone marrow cells in coculture studies with normal marrow. The patient's serum, when added to the culture of normal bone marrow cells, produced a marked decrease in CFU-C. Treatment with combination chemotherapy (prednisone, cyclophosphamide, and vincristine) produced a clinical response with correction of the leukopenia. Post-treatment serum did not produce a significant reduction in CFU-C from normal bone marrow.

Antineoplastic Agents↗
PubMed1983

Inhibition of food iron absorption by coffee.

Dual isotope studies were performed in iron replete human subjects to evaluate the effect of coffee on nonheme iron absorption. A cup of coffee reduced iron absorption from a hamburger meal by 39% as compared to a 64% decrease with tea, which is known to be a potent inhibitor of iron absorption. When a cup of drip coffee or instant coffee was ingested with a meal composed of semipurified ingredients, absorption was reduced from 5.88% to 1.64 and 0.97%, respectively, and when the strength of the instant coffee was doubled, percentage iron absorption fell to 0.53%. No decrease in iron absorption occurred when coffee was consumed 1 h before a meal, but the same degree of inhibition as with simultaneous ingestion was seen when coffee was taken 1 h later. In tests containing no food items, iron absorption from NaFeEDTA was diminished to the same extent as that from ferric chloride when each was added to a cup of coffee. These studies demonstrate that coffee inhibits iron absorption in a concentration-dependent fashion.

Adolescent↗
PubMed1983

Effect of fiber on nonheme iron absorption.

The effect of fiber on the absorption of food iron was examined by performing multiple radioiron absorption tests in normal male and female subjects. In an initial study, we added bran, pectin, or cellulose to muffins prepared with wheat flour. Because of the low values obtained in this study, another study was done in which apple juice containing 50 mg of ascorbic acid was added to the meal to increase iron absorption averaged 2.26% from plain muffins, 1.07% from bran muffins, 1.89% from pectin muffins, and 2.26% from cellulose muffins. Only the effect of bran was statistically significant. We next designed two complex meals that differed maximally in their content of naturally occurring fiber but that were matched with respect to macronutrient, mineral, iron, and ascorbic acid contents. Mean absorptions from the low- and high-fiber meals were significantly different, averaging 6.07% and 2.96%, respectively. These results demonstrate that inhibition of iron absorption is not a universal property of all fiber sources. Moreover, the relatively modest effect of maximally altering the natural fiber content of a meal suggests that fiber is not a major determinant of food iron availability in humans.

Adolescent↗
PubMed1983

The effect of food consistency on iron absorption.

Iron absorption and the half-time of gastric emptying were measured concurrently in 13 normal volunteer subjects. Each subject ate two test meals of identical composition; one meal was prepared and served in the usual manner while the second was homogenized before serving. No correlation was found between the half-time of gastric emptying and the absorption of either heme or nonheme iron among subjects eating the conventional meal. Homogenization of the meal led to a 31% fall in the mean half-time of gastric emptying and an increase in iron absorption of 22% for nonheme and 42% for heme. These findings indicate that the physical form of a meal has a modest effect on iron absorption.

Adult↗