R. W. Charlton

The effects of organic acids, phytates and polyphenols on the absorption of iron from vegetables

1. Non-haem iron absorption from a variety of vegetable meals was studied in parous Indian Women, using the erythrocyte utilization of radioactive Fe method. 2. The studies were undertaken to establish whether Fe absorption could be correlatedwith the chemical composition of the foodstuff. 3. Addition of the following organic acids commonly found in vegetables, improved the geometric mean Fe absorption from a basic rice meal as follows: from 0·028 to 0·085 with 1 g citric acid, from 0·031 to 0·081 with 15 mg ascorbic acid, from 0·048 to 0·095 with 1 g L-malic acid, from 0·041 to 0·096 with 1 g tartaric acid. The only exception was oxalic acid; the addition of 1 g calciumoxalate to cabbage ( Brassica oleraceae ) was associated with some depression in Fe absorption from 0·320 to 0·195. 4. There was a marked inhibition of the geometric mean absorption when 500 mg tannic acid was added to a broccoli ( Brassica oleraceae ) meal (0·015 v . 0·297). Sodium phytate (2 g) caused a similar, though less profound inhibition (0·035 to 0·152). 5. When 3 mg ferrous sulphate was added to different vegetables the geometric mean absorption varied widely. Vegetables of low Fe bioavailability were wheat germ ( Triticum aestivum ) 0·007, aubergine ( Solanum melongena ) 0·007, butter beans ( Phaseolus lunatus ) 0·012, spinach ( Spinacea oleraceae ) 0·014, brown lentils ( Lens culinaris ) 0·024, beetroot greens ( Beta vulgaris ) 0·024 and green lentils ( Lens culinaris ) 0·032. In contrast, bioavailability was moderate or good with carrot ( Daucus carota ) 0·098, potato ( Solanum tuberosum ) 0·115, beetroot ( Beta vulgaris ) 0·185, pumpkin ( Cucurbita mixta ) 0·206, broccoli 0·260, tomato ( Lycopersicon esculentum ) 0·224, cauliflower ( Brassica oleraceae ) 0·263, cabbage 0·320, turnip ( Brassica rapa ) 0·327 and sauerkraut 0·327. 6. All the vegetables associated with moderate or good Fe bioavailability contained appreciable amounts of one or more of the organic acids, malic, citric and ascorbic acids. 7. Poor Fe bioavailability was noted in vegetables with high phytate contents (e.g. wheat germ 0·007, butter beans 0·012, brown lentils 0·024 and green lentils 0·032). 8. The fact that a number of vegetables associated with low Fe-absorption turned bluish-black when Fe was added to them, suggested that the total polyphenol content in them was high. The vegetables included aubergine spinach, brown lentils, green lentils and beetroot greens. When the total polyphenol content in all the vegetables tested was formally measured, there was a significant inverse correlation (r 0·859, P r 0·901 (P 9. The major relevance of these findings is the fact that the total absorption of non-haem-Fe from a mixed diet may be profoundly influenced by the presence of single vegetables with either marked enhancing or inhibiting effects on Fe bioavailability.

Body iron excretion in man: a collaborative study.

Abstract A collaborative study was undertaken in an attempt to document obligatory iron losses in adult male subjects, using a variety of isotopic and chemical methods. Total body excretion was measured in four groups of subjects by injecting Fe 55 intravenously and following the decline in red cell activity over several years. Calculated daily iron losses were as follows: Seattle white subjects (group I) 0.95 mg. (±0.30); Venezuelan Mestizos (group II) 0.90 mg. (±0.31); Johannesburg Bantu (group III) 2.42 mg. (±1.09); Durban Indians (group IV) 1.02 mg. (±0.22); and Durban Bantu (group V) 2.01 mg. (±0.94). The higher values in the Bantu subjects were ascribed to the greater than normal iron stores in this population group. That losses in the Durban Indian subjects, who were working in an extremely hot and humid environment, were not greater than those in the white subjects suggests that excessive sweating does not represent a major route for iron excretion. The results of isotopic experiments to determine the quantities of iron lost via the gastrointestinal tract suggested a daily loss of approximately 0.1 mg. within desquamated mucosal cells and 0.4 mg. in blood. Chemical analyses of bile indicated a mean daily content of 0.26 mg. However, it was not possible to establish what proportion of this iron is reabsorbed into the body. Direct chemical measurements of iron in urine revealed a mean daily content of approximately 0.1 mg.; this quantity did not seem to be influenced by the size of the body stores. The amount of iron taken up daily from the plasma by eccrine skin at normal transferrin saturations was between 0.2 and 0.3 mg. When the transferrin saturation was high this figure rose to between 0.6 and 0.7 mg. In a final analysis, the calculated iron losses from individual compartments were added together and compared with those obtained in the long-term excretion study. Agreement was close in all but the Bantu groups. Even when maximum figures for individual compartmental losses were used, the figures were still lower than those obtained for total excretion. These discrepancies may reflect methodologic errors but it is equally possible that subjects with overload lose iron in ways other than those examined in the present study, such as bile and/or iron-loaded reticuloendothelial cells shed into the lumen of the gastrointestinal tract.

Clinical studyBody iron excretion in man: A collaborative study

Abstract A collaborative study was undertaken in an attempt to document obligatory iron losses in adult male subjects, using a variety of isotopic and chemical methods. Total body excretion was measured in four groups of subjects by injecting Fe 55 intravenously and following the decline in red cell activity over several years. Calculated daily iron losses were as follows: Seattle white subjects (group I) 0.95 mg. (±0.30); Venezuelan Mestizos (group II) 0.90 mg. (±0.31); Johannesburg Bantu (group III) 2.42 mg. (±1.09); Durban Indians (group IV) 1.02 mg. (±0.22); and Durban Bantu (group V) 2.01 mg. (±0.94). The higher values in the Bantu subjects were ascribed to the greater than normal iron stores in this population group. That losses in the Durban Indian subjects, who were working in an extremely hot and humid environment, were not greater than those in the white subjects suggests that excessive sweating does not represent a major route for iron excretion. The results of isotopic experiments to determine the quantities of iron lost via the gastrointestinal tract suggested a daily loss of approximately 0.1 mg. within desquamated mucosal cells and 0.4 mg. in blood. Chemical analyses of bile indicated a mean daily content of 0.26 mg. However, it was not possible to establish what proportion of this iron is reabsorbed into the body. Direct chemical measurements of iron in urine revealed a mean daily content of approximately 0.1 mg.; this quantity did not seem to be influenced by the size of the body stores. The amount of iron taken up daily from the plasma by eccrine skin at normal transferrin saturations was between 0.2 and 0.3 mg. When the transferrin saturation was high this figure rose to between 0.6 and 0.7 mg. In a final analysis, the calculated iron losses from individual compartments were added together and compared with those obtained in the long-term excretion study. Agreement was close in all but the Bantu groups. Even when maximum figures for individual compartmental losses were used, the figures were still lower than those obtained for total excretion. These discrepancies may reflect methodologic errors but it is equally possible that subjects with overload lose iron in ways other than those examined in the present study, such as bile and/or iron-loaded reticuloendothelial cells shed into the lumen of the gastrointestinal tract.

Factors affecting the absorption of iron from cereals

Non-haem-iron absorption from a variety of cereal and fibre meals was measured in parous Indian women, using the erythrocyte utilization of radioactive Fe method. The present study was undertaken to establish whether alteration of the phytate and polyphenol contents of sorghum (Sorghum vulgare) affected Fe absorption from sorghum meals, and to assess the influence of fibre on Fe absorption. Removing the outer layers of sorghum grain by pearling reduced the polyphenol and phytate contents by 96 and 92% respectively. This treatment significantly increased the geometric mean Fe absorption from 0.017 to 0.035 (t 3.9, P less than 0.005). The geometric mean Fe absorption from a sorghum cultivar that lacked polyphenols (albino sorghum) was 0.043, which was significantly greater than the 0.019 absorbed from bird-proof sorghum, a cultivar with a high polyphenol content (t 2.83, P less than 0.05). Fe was less well absorbed from the phytate-rich pearlings of the albino sorghum than from the pearled albino sorghum (0.015 v. 0.035 (t 8.4, P less than 0.0005]. Addition of sodium phytate to a highly Fe-bioavailable broccoli (Brassica oleracea) meal reduced Fe absorption from 0.185 to 0.037. The geometric mean Fe absorption from malted sorghum porridge was 0.024 when 9.5 mg ascorbic acid were added and 0.094 when the ascorbic acid was increased to 50 mg (t 3.33, P less than 0.005). This enhancing effect of 50 mg ascorbic acid was significantly depressed to 0.04 by tea (t 38.1, P less than 0.0005).(ABSTRACT TRUNCATED AT 250 WORDS)

Iron absorption from a cereal-based meal containing cane sugar fortified with ascorbic acid

1. The feasibility of improving iron nutrition by fortifying cane sugar with ascorbic acid was studied. 2. The absorption of Fe added to maize-weal porridge was measured in 116 volunteer multiparous Indian women using the radio-Fe erythrocyte utilization method. The meals were fed with and without tea or coffee and with and without varying amounts of ascorbic acid. 3. The mean absorption of Fe from maize-meal porridge was very low (3.8 %), being even further reduced (2.1 %) when tea was drunk with the meal. 4. The addition of 50 or 100 mg ascorbic acid to maize-meal porridge caused approximately a 10-fold increase in Fe absorption. The increase was much less when tea was present, being 2-fold and 5-fold with 50 and 100 mg ascorbic acid respectively. The inhibitory effect of tea on Fe absorption could, however, be overcome by giving larger doses of ascorbic acid (250 and 500 mg). 5. When contaminating Fe (2.5 mg) in the form of labelled rust (Fe,O,) or ferric hydroxide was added to maize-meal porridge it was poorly absorbed (mean values were 0.01 % and 1.5 % respectively). The addition of 100 mg ascorbic acid increased the mean Fe absorption rates to 0.5 % and 6.7 %with Fep03 and Fe(OH), respectively. Fe(OH), was found to be absorbed about half as well as the intrinsic Fe present in maize-meal porridge. 6. It is concluded that ascorbic acid is capable of improving Fe absorption from a cereal source. It can partially overcome the inhibitory effect of tea and might be expected to facilitate the absorption of at least some forms of Fe that may contaminate food. Current methods aimed at promoting adequate iron nutrition in communities that are at risk of Fe deficiency have relied on the fortification of dietary staples with added Fe. How

Factors affecting the absorption of iron from Fe(III)EDTA

1. The modification of iron absorption from Fe(III)EDTA by agents known to promote or inhibit absorption was examined in 101 volunteer multiparous Indian women. Fe absorption from Fe(III)EDTA was compared with absorption of intrinsic food Fe in a further twenty-eight subjects. Finally the urinary excretion of radio-Fe after oral administration of 59Fe(III)EDTA was studied in twenty-four subjects and evidence of intraluminal exchange of Fe was examined. 2. Fe absorption from maize porridge fortified with Fe(III)EDTA was more than twice that from porridge fortified with FeSO4 . 7H2O. 3. Although bran decreased Fe absorption from FeSO4 . 7H2O approximately 11-fold, it had no significant effect on Fe absorption from Fe(III)EDTA. Nevertheless tea, which is a more potent inhibitor of Fe absorption, decreased absorption from Fe(III)EDTA 7-fold. 4. Fe absorption from Fe(III)EDTA given in water was only increased 40% by addition of 3 mol ascorbic acid/mol Fe but by 7-fold when the relative proportions were increased to 6:1. This enhancing effect was blunted when the Fe(III)EDTA was given with maize porridge. In these circumstances, an ascorbate:iron value of 3:1 (which doubles absorption from FeSO4 . 7H2O) produced no significant increase in Fe absorption, while a value of 6:1 produced only a 2 . 5-fold increase. 5. Fe absorption from Fe(III)EDTA was not altered by addition of maize porridge unless ascorbic acid was present. 6. Less than 1% of 59Fe administered as 59Fe(III)EDTA was excreted in the urine and there was no inverse relationship between Fe absorption and the amounts excreted (r 0 . 58, P less than 0 . 05). 7. Isotope exchange between 59Fe(III)EDTA and 59FeSO4 . 7H2O was demonstrated by finding a similar relative value for the two isotopes in urine and erythrocytes when the two labelled compounds were given together orally. This finding was confirmed by in vitro studies, which showed enhanced 59Fe solubilization from 59FeSO4 . 7H2O in maize porridge when unlabelled Fe(III)EDTA was added. 8. Although Fe absorption from Fe(III)EDTA was marginally higher it appeared to form a common pool with intrinsic food iron in most studies. It is postulated that the mechanism whereby Fe(III)EDTA forms a common pool with intrinsic food Fe differs from that occurring with simple Fe salts. When Fe is present in the chelated form it remains in solution and is relatively well absorbed because it is protected from inhibitory ligands. Simple Fe salts, however, are not similarly protected and are absorbed as poorly as the intrinsic food Fe. 9. It is concluded that Fe(III)EDTA may be a useful compound for food fortification of cereals because the Fe is well absorbed and utilized for haemoglobin synthesis. The substances in cereals which inhibit absorption of simple Fe salts do not appear to inhibit absorption of Fe from Fe(III)EDTA.

Iron absorption from rice meals cooked with fortified salt containing ferrous sulphate and ascorbic acid

1. Iron absorption from rice-containing meals was measured by red cell utilization of radioactive Fe in sixty-six volunteer multiparous Indian women. 2. In all the studies salt added during the cooking process was used as the carrier for supplemental inorganic Fe and ascorbic acid. 3. Intrinsic Fe in the rice and supplementary inorganic Fe were absorbed to the same extent, with a wide range of absorption values. 4. There was a striking difference between the mean absorption of a 3 mg dose of ferrous Fe given to fasting subjects in a solution containing 30 mg ascorbic acid and that of Fe in a rice meal (48.7 and 3.5% respectively). 5. When ascorbic acid was added during cooking there was a threefold increase in the absorption of both intrinsic Fe and supplementary Fe when a sufficient quantity (60 mg) was present. 6. It is concluded that the Fe nutrition of rice-eating communities could be improved significantly by the addition of ascorbic acid to the diet.

Some Factors Affecting the Release of Iron from Reticuloendothelial Cells

Summary. Factors modifying the release of iron from reticuloendothelial cells were studied in rats by injecting heat‐denatured erythrocytes containing [59Fe]haemoglobin. The cells were rapidly taken up by the liver and spleen, and a proportion of the 59Fe was released into the plasma, the maximum rate being between 1 and 4 hr after injection. The remaining 59Fe was incorporated into storage compounds. A 10‐fold variation in the load of denatured erythrocytes produced a proportional change in the amount of iron released, the percentage remaining constant. Percentage release of 59Fe was enhanced in venesected rats and diminished in hypertransfused rats. Release was inhibited by injecting either unlabelled denatured erythrocytes or iron bound with nitrilotriacetic acid (NTA‐iron) before the 59Fe‐labelled cells, the maximum effect being obtained if the interval between the two injections was 3‐9 hr. Release was also inhibited by injecting NTA‐iron 30 min after the denatured labelled erythrocytes. Inhibition was always preceded by a rise in the serum‐iron concentration, and was associated with an increase in the percentage of 59Fe incorporated into ferritin. It is postulated that the shortage of free transferrin binding sites for iron delays the entry of liberated haemoglobin iron into the plasma, and consequently there is enlargement of a ‘pre‐release’ iron pool. Other workers have shown that iron induces the synthesis of ferritin; the presence of a stimulated mechanism for ferritin synthesis within the reticuloendothelial cells would result in the diversion of an increased percentage of erythrocyte iron into storage compounds.

The Effect of Ascorbic Acid Deficiency on Desferrioxamine‐Induced Urinary Iron Excretion

Summary. The levels of tissue ascorbic acid tend to be low in subjects with iron overload. The present study was undertaken to find out whether this ascorbic acid deficiency affected the quantities of iron excreted in the urine after the administration of the iron chelate, desferrioxamine. Basal tests were done and were then repeated after 7 days of ascorbic acid therapy. Desferrioxamine‐induced urinary iron excretion increased by 88 per cent in 13 individuals with transfusional siderosis, 60 per cent in five with idiopathic haemochromatosis and 350 per cent in 12 Bantu subjects with dietary siderosis. Over the same period the mean leucocyte ascorbic acid concentrations rose by 164 per cent, 157 per cent and 551 per cent respectively. In contrast, no change was noted in either urinary iron excretion or in ascorbic acid concentrations in six normal white and six normal Bantu control subjects. These results suggest that tissue ascorbic acid concentrations should be restored to normal before desferrioxamine is used for either the diagnosis or the treatment of iron overload.

Iron absorption from maize ( Zea mays ) and sorghum ( Sorghum vulgare ) beer

1. Iron absorption from maize (Zea mays) and sorghum (Sorghum vulgare) beer was more than twelve-fold greater than from a gruel made from the constituents used to prepare the beer. 2. The effect of changes occurring during brewing were investigated. These changes include a decrease in the solid content, and the formation of 30 ml ethanol/1 and 5 ml lactic acid/1. 3. The presence of solid material was found to inhibit Fe absorption markedly, especially when the solid content was 100 g/l or more. 4. The presence of ethanol potentiated Fe absorption but the effect was only modest in gruels with a high solid content. 5. Fe absorption from a 2 ml lactic acid/l solution was four-fold greater than from a hydrochloric acid solution of the same pH. When lactic acid was added to a gruel containing 200 g solids/l the mean absorbtion rose from 0.4 to 1.2 %. 6. In a direct comparison, Fe absorption from beer was significantly better than from a gruel of similar pH containing lactic acid. 7. The results suggest that at least three factors are responsible for the enhanced Fe absorption from maize and sorghum beer. These include the removal of solids during fermentation and the presence of ethanol and of lactic acid in the final brew. 8. In order to reproduce the way in which beer is brewed domestically in Fe containers, a study was done in which beer was prepared in the presence of Fe wire. Under such circumstances Fe was rapidly dissolved and the final Fe concentration of the brew was 89 mg/l. However, the nature of the Fe-containing compound or compounds was not elucidated.