Biomedical subjects

L Hallberg

Publications and source records attributed to L Hallberg.

At least 55 records · Page 3Linked to original sources

PubMed1992

Iron requirements. Comments on methods and some crucial concepts in iron nutrition.

Absorbed iron (Fe) requirements are partly recalculated based on new figures for Fe requirements in menstruating women. The new higher figures were obtained by including in the calculation of the total requirements the effect of variations in hemoglobin concentration, which influences the variation in menstrual Fe losses and the variation in basal Fe losses. Higher figures were also found for menstruating teenage girls. Dietary iron requirements were also recalculated based on a critical examination of data available allowing estimations of bioavailability of the dietary iron in Western-type diets. In borderline Fe-deficient subjects, with optimal hemoglobin levels but no iron stores, the 95th percentile range for the bioavailability was estimated to 14-16% of the fraction of the dietary Fe that is potentially available for absorption (correction for partially available fortification Fe).

Adolescent↗

PubMed1992

Iron absorption from bread in humans: inhibiting effects of cereal fiber, phytate and inositol phosphates with different numbers of phosphate groups.

Iron absorption was measured from five kinds of bread made from various types of flour and fermented in different ways in order to obtain a wide variation in the content of fiber, phytate (inositol hexaphosphate) and its degradation products, inorganic phosphate and inositol phosphates with fewer numbers of phosphate groups (inositol pentaphosphate through monophosphate). Each experiment had 9-10 subjects and, in each subject, iron absorption was measured from control rolls made from low extraction wheat flour and one kind of test roll using two different radioiron tracers: 55Fe and 59Fe. The inhibition of iron absorption was closely related to the content of phytate-phosphorous as determined using the AOAC method, and to the sum of the tri- through hexaphosphate groups as determined using the HPLC method. As an example, prolonged fermentation of whole-rye bread reduced total inositol phosphates to the same amount as in the control rolls and increased fractional iron absorption to the same high level, in spite of a fiber content five times as great. The results strongly suggest that the inhibitory effect of bran on iron absorption is due to its content of phytate and other inositol phosphates present after fermentation, rather than to its content of fiber or other constituents. Thus, effective fermentation will increase the bioavailability of iron in whole-meal bread.

Absorption↗

PubMed1992

Bioavailability in man of iron in human milk and cow's milk in relation to their calcium contents.

Iron absorption from human milk and cow's milk was compared in the same subjects using two radio-iron tracers and extrinsic labeling of the iron. Previously observed higher iron absorption from human milk was confirmed as 19.5 +/- 17.3% (mean +/- SD) in cow's milk versus 48.0 +/- 25.5% in human milk; mean individual absorption ratio was 0.39 +/- 0.18 (p less than 0.0001). Cow's milk has a several times higher content of calcium, recently established to be a potent inhibitor of iron absorption. Adding calcium chloride to human milk in amounts to equate the calcium content of cow's milk significantly reduced iron absorption [39.1 +/- 17.8% (mean +/- SD) versus 21.3 +/- 10.6%]; mean individual absorption ratio with or without added calcium was 0.58 +/- 0.12 (mean +/- SD) (p less than 0.0001). Differences in calcium content could explain at least 70% of the difference in iron bioavailability between milks. It is suggested that the remaining 30% difference may mainly be an artifact related to inhomogeneous radioiron-labeling of milk iron compounds, especially in human milk, and that the main difference in true iron absorption between human and cow's milk is related to their different calcium contents. The rather high fractional iron absorption from human milk can be explained by its low iron content. There is nothing to indicate that human milk contains any enhancer of iron absorption. The marked inhibiting effect of calcium on iron absorption should be considered in the design of infant formulas to achieve an optimal balance in the contents of calcium and iron.

Adult↗

PubMed1992

Psychometric evaluation of the hearing measurement scale on patients registered in a Swedish hearing centre.

The hearing measurement scale (HMS), targeting the experience of being hearing impaired, was translated into Swedish and answered by 122 patients with slight to moderate hearing losses. According to the item analysis the test construction of the HMS functions well with a relevant division of the sections. In all sections there were individuals utilizing all response possibilities and the homogeneity (alpha) of the test was high. One exception was section II (hearing non-verbal sounds), which may be due to lack of awareness, indicating that it might not be possible to pursue this dimension by a questionnaire approach. Normative descriptions were given for two age groups: 40 to 60 and 61 to 74 years, including both sexes. The groups had a similar outcome on the HMS, even though the older subjects, on average, had worse hearing problems, measured by pure-tone audiometry. The section covering speech perception had the strongest correlation with hearing loss, while the section covering emotional response entirely lacked such correlations for the younger group.

Age Factors↗

PubMed1992

Calcium and iron absorption: mechanism of action and nutritional importance.

We investigated the inhibitory effect of calcium on iron absorption in 57 human subjects. Three studies suggested that the effect is not located in the gastrointestinal tract. The presence of phytate in a meal and formation of calcium-iron-phytate complexes is not a prerequisite for the inhibition. The relative increase in iron absorption by ascorbic acid was the same in meals with and without calcium, suggesting that calcium did not influence the balance between enhancing and inhibiting ligands in the gastrointestinal lumen. No inhibiting effect on iron absorption was seen when adding 3 mg calcium to 0.01 mg iron (molar ratio Ca/Fe = 420). Previous studies showing a marked inhibition by calcium had a lower molar ratio, but greater amounts of calcium were given. This suggests that a minimal concentration of calcium is needed to achieve an effect. The present results indirectly support our original hypothesis that the inhibitory effect of calcium on iron absorption is situated within the intestinal mucosal cells. The practical nutritional implications of the inhibitory effect of calcium are considerable since addition of milk, milkshake or cheese to common meals such as pizza or hamburger meals reduced iron absorption by 50-60%. It is recommended to reduce the intake of dairy products with the main meals providing most of the dietary iron, especially for those having the highest iron requirements i.e. children, teenagers and women at childbearing age.

Adult↗

PubMed1991

Calcium: effect of different amounts on nonheme- and heme-iron absorption in humans.

We investigated the effect of calcium on iron absorption in 126 human subjects. Addition of calcium chloride to wheat rolls significantly reduced iron absorption. Doses between 40 and 600 mg Ca were studied. The inhibition was clearly dose related up to 300 mg Ca. Calcium added to the dough when making the rolls reduced phytate degradation during fermentation and baking. As little as 40 mg Ca added to 80 g flour reduced phytate degradation by 50%, thus increasing the phytate content of the rolls to levels interfering with iron absorption. Calcium also had a direct dose-related inhibiting effect on iron absorption, noted by adding calcium to the rolls after they had been baked instead of to the dough. Iron absorption was reduced by 50-60% at doses of 300-600 mg Ca. Giving 165 mg Ca as milk, cheese, or calcium chloride reduced absorption by 50-60%. The same amount of calcium also significantly reduced heme-iron absorption, suggesting that the effect of calcium is related to the mucosal transfer of iron. The observed marked inhibitory effect on iron absorption of calcium in amounts frequently encountered in normal meals has important nutritional implications.

Absorption↗

PubMed1991

Dose-dependent inhibitory effect of phenolic compounds in foods on nonheme-iron absorption in men.

Nonheme-iron absorption from a typical Southeast Asian meal was studied to examine the effect of a common vegetable, Yod Kratin, which contains a considerable amount of iron-binding phenolic groups. Yod Kratin (leaves of the lead tree) is a very popular vegetable in Thailand. It is consumed at least once a week year round, sometimes every day, together with the main meal. With a common portion size of the vegetable (20 g), iron absorption was reduced by almost 90%. As little as 5 g inhibited iron absorption by 75%. Addition of ascorbic acid partly counteracted inhibition. Adding 100 mg ascorbic acid reduced inhibition of iron absorption from 5 g Yod Kratin by half and the inhibition from 10 g Yod Kratin by a quarter. The study illustrates the marked effect of iron-binding phenolic compounds on iron nutrition and, thus, the importance of acquiring knowledge of the content of such compounds in different foods.

Absorption↗

PubMed1991

Competitive inhibition of iron absorption by manganese and zinc in humans.

Zinc and manganese may interfere with iron absorption because of similar physicochemical properties and shared absorptive pathways. The effects of zinc and manganese on iron absorption were studied in human subjects by using paired observations and a dual-radioisotope method (55Fe and 49Fe). Manganese inhibited iron absorption both in solutions and in a hamburger meal. Fractional iron absorption is strongly dose dependent. Adding 2.99 mg Mn to 0.01 mg Fe reduced iron absorption to the same extent as increasing the iron dose 300-fold to 3 mg, strongly indicating a direct competitive inhibition of manganese on iron absorption. In the same experiment with zinc, no inhibitory effect was observed, suggesting different pathways for the absorption of zinc and iron. An intraluminal interaction may occur, because a fivefold excess of zinc to iron (15 mgZn/3 mg Fe) reduced iron absorption by 56% when given in a water solution but not when given with a hamburger meal.

Absorption↗

PubMed1991

Iron requirements in menstruating women.

Total-absorbed-iron requirements in adult and teen-age menstruating women were calculated from previously published data on menstrual blood losses; hemoglobin distribution in healthy, nonanemic women; basal iron losses; and growth requirements in teen-agers. Because present calculations included the effect of the variation of all indices, the new requirements for iron were increased to 2.84 mg/d in adult women and 3.21 mg/d in teen-agers (95th percentiles). Six independent estimations of whole-diet iron bioavailability were made to translate absorbed iron requirements into dietary requirements. In subjects with no iron stores, estimated dietary iron bioavailability amounted to 14% (Swedish diet), 16% (French diet), and 16.6% (US diet). When 15% was used as a single figure to represent the optimal, long-term bioavailability of iron in a general Western-type diet, the 95th percentiles of dietary iron requirements were 18.9 mg in adult menstruating women and 21.4 mg in menstruating teenagers.

Absorption↗

PubMed1990

Inhibitory effect of oat products on non-haem iron absorption in man.

Oat products are increasingly used in human nutrition due to the rather high content of soluble fibre. Oat products, however, have a high content of phytate which may interfere with the absorption of non-haem iron. The iron balance situation is critical in several groups, especially in children, teenagers and women in their fertile years. It is therefore important to examine the effect of oat products on non-haem iron absorption in man. The present studies showed that oat bran and oat porridge markedly inhibited the absorption of non-haem iron. The inhibition can be explained by the high phytate content of oat products. This is partly due to a high resistance of oat phytate against exogenous phytase and partly to an inactivation of the endogenous phytase in oats caused by the usual heat treatment of oats which is made to prevent rancidity of oat lipids during storage. The inhibitory effect of oat products on iron absorption is sufficiently marked to be a serious consideration if such products are more regularly consumed.

Adult↗

PubMed1990

Rice and iron absorption in man.

Several studies suggest that iron absorption is low from rice-based meals. Comparisons of the effect of rice starch and wheat starch on iron absorption showed that rice had no effect on absorption. Observed differences in effects on iron absorption between different batches of rice starch could be explained by differences in the phytate content. Phytate is always present in rice grains. The content varies markedly depending on the method of milling. In polished rice, the content of phytate-P varied between 11.5 and 66 mg/100 g rice (data from 45 rice mills in Thailand). The bioavailability of iron in a meal composed of meat, a vegetable and rice varied about threefold (22.1-7.5 per cent) depending on the different phytate content of the rice (4 levels between 30 and 175 mg phytate-P were studied). The inhibitory effect of the phytate in rice was overcome by adding different amounts of an ascorbic acid-rich vegetable (green collard) to the meals.

Biological Availability↗

PubMed1989

Genotoxicity of azidoalanine in mammalian cells.

Sodium azide mutagenesis is mediated through a metabolic intermediate in bacteria and plant species. However, very little is known about the interaction of this intermediate with nucleic acids, its genotoxic potential, or its mechanism of action, especially in mammalian cells. Chinese hamster cells and normal human skin fibroblasts were treated with extracts from Salmonella typhimurium or Hordeum vulgare (barley) containing a crude mutagenic metabolite, as well as with synthetically produced azidoalanine. The cells were evaluated for the induction of sister chromatid exchanges and the ability to perform unscheduled DNA synthesis. With the purified azidoalanine and the azide-treated extracts from Hordeum vulgare, there was a statistically significant increase in the frequency of sister chromatid exchanges observed in both Chinese hamster cells and human fibroblasts. This increase was about twofold, as compared with the control. On the other hand, there was no detectable genotoxic response when cells were exposed to azide-treated extract from Salmonella typhimurium. The results imply that azidoalanine and the crude mutagenic metabolite from Hordeum vulgare are weakly genotoxic in mammalian cells.

Alanine↗

PubMed1989

Sodium azide mutagenesis in mammals: inability of mammalian cells to convert azide to a mutagenic intermediate.

Sodium azide is unique among mutagens. It is highly mutagenic in many plant and bacterial species but marginally mutagenic in mammalian cells. A possible explanation for this difference in mutagenic efficiency may lie in the inability of mammalian cells to convert azide to the putative ultimate mutagen. Normal human fibroblasts and Chinese hamster cells or cell-free extracts from these cell lines were treated with azide and the sonicates tested for mutagenicity in Salmonella strain TA1530. The data suggest that neither cell line was capable of converting azide to a mutagenic intermediate. In addition, both cell lines expressed the enzyme O-acetylserine(thio)-lyase which is responsible for the conversion of azide to azidoalanine, the putative mutagenic intermediate. Although mammalian cells possess the enzyme responsible for the conversion of azide to azidoalanine, they appear incapable of converting azide into a mutagenic intermediate in appreciable quantities. Further, the data support the conclusion that azide may be further modified in mammalian cells to an intermediate that is not genotoxic.

Animals↗

PubMed1989

Iron absorption in man: ascorbic acid and dose-dependent inhibition by phytate.

The dose-dependent inhibitory effect of sodium phytate on iron absorption was studied in man by serving wheat rolls containing no phytates and rolls to which various amounts (seven dose levels between 2 and 250 mg expressed as phytate phosphorus) were added just before serving. Fe in the two kinds of rolls was labeled with two radioisotopes of Fe (55Fe, 59Fe) and the rolls were served on alternate days. The inhibition of Fe absorption was strongly related to the amount of phytate added; 2 mg inhibited absorption by 18%, (p less than 0.001), 25 mg by 64% (p less than 0.001), and 250 mg by 82% (p less than 0.001). The addition of ascorbic acid significantly counteracted the inhibition whereas the corresponding effect of meat was less well defined and only seen at the highest phytate level. The marked inhibition of Fe absorption by phytates and the significant counteracting effect of ascorbic acid have wide nutritional implications.

Adult↗

PubMed1989

Iron absorption: no intestinal adaptation to a high-phytate diet.

The present study examined the possibility that a high bran and phytate intake over a long period would induce changes in the intestines or its microflora leading to a reduction of the inhibitory effect of dietary phytates on iron absorption. Such changes might occur in vegetarians and populations in developing countries with a usually very high dietary intake of phytates. The inhibitory effect of bran on Fe absorption was compared between a group of strict vegetarians with a regular high phytate intake and a control group by use of wheat rolls with and without bran labeled with 55Fe and 59Fe. The average individual decrease of the Fe absorption from adding the bran was 92 and 93% in the two groups, respectively. No intestinal adaptation to a high phytate intake could be observed. This finding has wide nutritional implications.

Adaptation, Physiological↗

PubMed1989

Iron fortification of flour with a complex ferric orthophosphate.

The unexpectedly low bioavailability in humans of elemental iron powder prompted us to search for other Fe compounds suitable for Fe fortification of flour that fulfill the two requirements of insolubility in water (due to high water content of flour) and good bioavailability in humans. Systematic studies of compatibility, solubility, and bioavailability led to this study of a microcrystalline complex ferric orthophosphate (CFOP), Fe3H8(NH4)-(PO4)6.6H2O, a well-defined compound. This compound was labeled with 59Fe, and the native Fe in meals was labeled with 55FeCl3. The ratio of absorbed 59Fe to absorbed 55Fe is a direct measure of the fraction of CFOP that joins the nonheme Fe pool and that is made potentially available for absorption. The relative bioavailability of CFOP varied from 30% to 60% when labeled wheat rolls were served with different meals. The CFOP meets practical requirements of an Fe fortificant for flour well, with regard to both compatibility and bioavailability in humans.

Adult↗

PubMed1989

Search for nutritional confounding factors in the relationship between iron deficiency and brain function.

This paper on confounding factors in the relationship between iron deficiency and brain function is mainly limited to nutritional factors, primarily factors that can contribute to the development of iron deficiency and that may have an independent direct action on brain function. Three theoretically possible confounders were found in a systematic search for dietary factors: 1) low intake of ascorbic acid, 2) excess of phytates, and 3) increased absorption of lead. Ascorbic acid has a marked effect on the bioavailability of dietary iron and is also known to directly influence various metabolic processes in the brain. Phytates inhibit the absorption not only of iron but also of zinc. An iron deficiency may thus be accompanied by a zinc deficiency which may affect mental performance. A state of iron deficiency may increase the absorption of lead from the diet, which in turn may affect brain function.

Animals↗

PubMed1989

Prevalence of hereditary haemochromatosis in two Swedish urban areas.

The prevalence of hereditary haemochromatosis (HH) was studied in Stockholm and Göteborg, the two largest cities in Sweden, using screening with transferrin saturation in combination with serum ferritin and further clinical and laboratory examinations. In Göteborg, none of 1660 men aged 50 and 51 years, randomly selected from the census register, was found to have HH. In Stockholm, nine out of 11,920 male hospital inpatients were diagnosed as having HH. The calculated mean and 95% confidence ranges were consistent with earlier findings in two studies on men in Malmö, the third largest urban area in Sweden. Pooling results from these three main urban areas, the mean prevalence was 0.073% (17/23, 355), which is considerably lower than figures reported from one area in northern Sweden and from pedigree analyses in several other areas in the world. Screening of the US population in the N-HANES II study also showed much lower figures. The reasons for these discrepancies are discussed and it is suggested that the average prevalence of HH in Caucasian populations is probably around 0.1%.

Hemochromatosis↗