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Biomedical subjects

L Hallberg

Publications and source records attributed to L Hallberg.

At least 73 records · Page 4Linked to original sources
PubMed1989

The population study of women in Gothenburg 1980-81--the third phase of a longitudinal study. Comparison between participants and non-participants.

A representative population sample comprising 1,462 women was studied in Gothenburg, Sweden in 1968-69, and a third follow-up study was carried out in 1980-81. The participation rates in the baseline study and during the follow-up studies were high. In 1980-81 women in two new age strata, aged 26 and 38, were added. Women who had moved to or from Gothenburg during the study period were not found to differ from those who were living in Gothenburg during the total study period, while there were a few differences of statistical significance between refusers and participants in 1980-81. The mortality among initial refusers was about doubled compared to that of those who participated in the baseline study.

Adult↗
PubMed1989

The role of vitamin C in iron absorption.

Iron requirements remain the same despite the current lower energy requirement. This means that more iron must be absorbed per unit energy. A higher bioavailability of the dietary iron can be achieved by increasing the content of food components enhancing iron absorption (ascorbic acid, meat/fish) or by decreasing the content of inhibitors (e.g., phytates, tannins). The latter is not feasible considering the recent and reasonable trend toward increasing the intake of dietary fibre. The key role of ascorbic acid for the absorption of dietary nonheme iron is generally accepted. The reasons for its action are twofold: (1) the prevention of the formation of insoluble and unabsorbable iron compounds and (2) the reduction of ferric to ferrous iron, which seems to be a requirement for the uptake of iron into the mucosal cells.

Ascorbic Acid↗
PubMed1989

Iron absorption and phenolic compounds: importance of different phenolic structures.

The phenolic compounds (phenolic monomers, polyphenols, tannins) are considered to interfere with iron absorption by complex formation with iron in the gastro-intestinal lumen, making the iron less available for absorption. Very little is known about the extent to which different types of phenolic compounds of different size and chemical structure inhibit iron absorption. The relationship between iron absorption and the amount and type of phenolic compounds was studied by the extrinsic tag method. The aims of the studies were as follows: (i) To study the effect of small phenolic compounds with different hydroxylation patterns (gallic acid, catechin, chlorogenic acid) on iron absorption, (ii) To study the effect of different amounts of a hydrolysable tannin containing ten gallic acid residues (tannic acid) on iron absorption. (iii) To study the degree of inhibition of iron absorption by some foods and beverages (oregano, spinach, coffee and tea) in relation to their respective content of iron-binding phenolic groups, measured by a newly developed method. The inhibition of iron absorption by tannic acid was strongly dose-related. The smallest amount (5 mg) inhibited absorption by 20 per cent, 25 mg by 67 per cent and 100 mg by 88 per cent. Gallic acid inhibited iron absorption to the same extent as tannic acid, per mol galloyl groups, whereas no inhibition was observed when catechin was added to the test meal. Chlorogenic acid inhibited iron absorption to a lesser extent. Oregano and tea inhibited iron absorption in proportion to their respective content of galloyl groups, whereas the inhibitory effect of spinach was less marked. The inhibiting effect of coffee was explained mainly by its content of galloyl groups, but also by some other factor, probably chlorogenic acid. It is concluded that the content of iron-binding galloyl groups might be a major determinant of the inhibitory effect of phenolic compounds on iron absorption from the diet, whereas the phenolic catechol groups seem to be of minor importance. The results further suggest that the group of condensed tannins do not interfere with iron absorption.

Absorption↗
PubMed1987

Phytates and the inhibitory effect of bran on iron absorption in man.

The cause of marked inhibitory effect of bran on absorption of dietary nonheme iron was studied in man by double-radioiron technique. Washing bran with hydrochloric acid but not with water removed inhibitory factor(s). Inhibition was almost restored by reconstituting phytate level. Removal of phytates in bran by endogenous phytase significantly increased absorption of iron. Removing, by washing with water, phosphates formed from phytates during enzymatic dephytinization led to a bran fraction with only a small remaining inhibitory effect on iron absorption. Half the iron in bran is in the form of monoferric phytate, which is well-absorbed. When potassium and magnesium phytates were added in amounts present in bran, the same inhibitory effect on iron absorption was seen. Although there appear to be other factors in bran that partly explain the inhibition, phytates are the main cause of the inhibitory effect of bran on iron absorption.

6-Phytase↗
PubMed1987

Is there a physiological role of vitamin C in iron absorption?

Nonheme iron usually constitutes more than 90% of the dietary iron. Its absorbability is a resultant of the balance between factors enhancing and inhibiting the absorption. Ascorbic acid is the most potent enhancer, and is the same for native and synthetic AA. The enhancing effect is strongly dose related (log dose/effect), and is different for different meals probably mainly due to varying content of inhibitors in the meals. AA also increases the iron absorption from simple meals with no known inhibitor, probably because AA impairs the formation of unavailable iron complexes with ligands normally present in the gastrointestinal lumen. The effect of AA is so unequivocal and marked that it must be considered as a physiological factor essential for the absorption of dietary iron.

Absorption↗
PubMed1987

Wheat fiber, phytates and iron absorption.

The marked inhibitory effect of bran on iron absorption can almost completely be explained by its content of phytates. There are other inhibiting factor(s) as well in bran but they play only a minor role especially in meat containing meals. Several studies were made to clarify the role of phytates. Enzymatic dephytinization of bran almost fully removed its inhibiting effect. The same was observed when washing bran with hydrochloric acid. A "physiological" mixture of monoferric, potassium and magnesium phytates showed the same inhibition of the absorption of iron as bran with the same phytate content. There was a strong semilogarithmic relationship (r = 0.99) between the inhibition of iron absorption and the amount of phytates. As little as 5-10 mg phytate phosphorus added to a wheat roll containing 3 mg iron inhibited iron absorption by 50 per cent. Ascorbic acid as well as meat strongly counteracted this inhibition. It was concluded that if bran is used to increase the dietary fiber intake that would interfere with the absorption of iron. However, if the intake of ascorbic acid and/or meat are sufficiently increased in the bran containing meals that would effectively counteract the inhibition of the iron absorption by the phytates in bran (wheat fiber).

Ascorbic Acid↗
PubMed1986

Low bioavailability of carbonyl iron in man: studies on iron fortification of wheat flour.

The bioavailability in man of commercially available elemental iron powders is unknown despite their extensive use for fortification of flour. Carbonyl iron, which is widely used in Europe, is considered as one of the best reduced iron powders based on studies both in vitro and in animals. In this study, a 55Fe labeled carbonyl iron was prepared by neutron irradiation and used to fortify wheat flour. The native iron of the wheat was extrinsically labeled by 59FeCl3. Doubly labeled wheat rolls were served with different meals. The ratio of absorbed 55Fe/59Fe is a direct measure of the fraction of carbonyl iron that joins the nonheme iron pool and is made potentially available for absorption. This relative bioavailability of carbonyl iron was unexpectedly low and varied from 20 to 5% when the iron fortified wheat rolls were served with different meals. The baking process did not change the relative bioavailability nor the addition of ascorbic acid. The low and variable bioavailability of carbonyl iron in man, makes it necessary to reconsider the rationale of using elemental iron powders for the fortification of foods for human consumption.

Adult↗
PubMed1986

Iron losses in sweat.

The losses of iron in whole body cell-free sweat were determined in eleven healthy men. A new experimental design was used with a very careful cleaning procedure of the skin and repeated consecutive sampling periods of sweat in a sauna. The purpose was to achieve a steady state of sweat iron losses with minimal influence from iron originating from desquamated cells and iron contaminating the skin. A steady state was reached in the third sauna period (second sweat sampling period). Iron loss was directly related to the volume of sweat lost and amounted to 22.5 micrograms iron/l sweat. The findings indicate that iron is a physiological constituent of sweat and derived not only from contamination. Present results imply that variations in the amount of sweat lost will have only a marginal effect on the variation in total body iron losses.

Adult↗
PubMed1986

Effect of ascorbic acid on iron absorption from different types of meals. Studies with ascorbic-acid-rich foods and synthetic ascorbic acid given in different amounts with different meals.

The effect of ascorbic acid on the absorption of non-heme iron was studied in 299 subjects. Different meals in which the non-heme iron was labelled with two different radio-iron isotopes were served with and without ascorbic acid to the same subject. Other meals containing foods with a known high content of ascorbic acid were also studied. Studies were also made giving different amounts of ascorbic acid with different meals. Marked differences in the enhancement of iron absorption were seen when ascorbic acid was given in different meals. It is suggested that ascorbic acid promotes iron absorption from the diet by reducing the negative effect on iron absorption of certain ligands such as phytates and tannins present in the diet. This interpretation is supported by observations that the most pronounced effects of ascorbic acid were found in meals with a high content of ligands known to inhibit iron absorption. Crystalline ascorbic acid and native ascorbic acid in foods appeared to have the same effect in promoting absorption of iron. The results indicate that ascorbic acid has a key physiologic role in facilitating the absorption of non-heme iron from the diet and that about 50 mg of the vitamin in each main meal is desirable for optimum effect.

Adult↗