Iron status in Swedish teenage girls: impact of low dietary iron bioavailability.

OBJECTIVE: Although it is well known that bioavailability of iron in the diet is important, it has not been fully elucidated in practice. We investigated iron intake and iron absorption in the ordinary diet of free-living individuals in relation to iron status and assessed iron requirements. METHODS: From a total of 1245 adolescent boys and girls included in the Göteborg Adolescence Study of food habits, 28 adolescent girls registered their food intake during 7 d. Iron intake was assessed on the basis of these 7-d dietary records. Iron absorption was calculated using an algorithm including enhancing and inhibiting dietary factors on iron absorption in relation to individual iron status. RESULTS: Available iron intake was 11.5 +/- 2.8 mg/d (mean +/- SD). The proportion of girls with an iron intake below the Nordic nutrition recommendations was 85% (n = 24). Calculated iron absorption was 1.09 +/- 0.59 mg/d (mean +/- SD). Only four girls satisfied their estimated individual iron requirement concerning the absorbed amount of iron. Iron depletion (serum ferritin concentration < or = 15 microg/L) was present in 10 girls (36%), 2 of whom were also anemic (hemoglobin concentration < or = 120 g/L). CONCLUSION: Swedish adolescent girls seemed to have difficulties satisfying their iron requirement in terms of absorbed amount. The data support the view that iron intake and bioavailability of dietary iron is important when evaluating whether iron requirements have been met.

No enhancing effect of vitamin A on iron absorption in humans.

BACKGROUND: Vitamin A and beta-carotene were recently reported to enhance iron absorption by counteracting the inhibitory effect of phytic acid in cereal-based meals and of polyphenol-containing beverages on nonheme-iron absorption in humans. OBJECTIVE: Our objective was to further evaluate the influence of vitamin A on iron absorption. DESIGN: Iron absorption from corn bread with or without added vitamin A (retinyl palmitate) was determined in 5 studies in young adult human subjects by using either a stable-isotope method (2 studies) or a radioisotope technique (3 studies). Iron absorption was measured by erythrocyte incorporation of the isotopic labels and by whole-body retention of (59)Fe. Corn bread was served with water (studies 1 and 3) or coffee (studies 2, 4, and 5). The studies differed in the amounts and chemical forms of added tracer and fortification iron. The possibility of methodologic artifacts in earlier investigations was evaluated. RESULTS: No effect of vitamin A on iron absorption from the test meals was identified in the individual studies by using paired Student's t test. A slightly negative effect of vitamin A on iron absorption was found with the use of analysis of variance. CONCLUSIONS: The previously reported findings of a positive effect of vitamin A on nonheme-iron absorption in humans was not confirmed. Incomplete isotopic equilibration of the tracer with native iron in the meal or with fortification iron cannot explain the previous findings. However, the present study does not exclude the possibility that suboptimal vitamin A status influences the effect of dietary vitamin A on iron absorption.

The usefulness of elemental iron for cereal flour fortification: a SUSTAIN Task Force report. Sharing United States Technology to Aid in the Improvement of Nutrition.

Fortification of cereal flours may be a useful public health strategy to combat iron deficiency. Cereal flours that are used shortly after production (e.g., baking flour) can be fortified with soluble iron compounds, such as ferrous sulfate, whereas the majority of flours stored for longer periods is usually fortified with elemental iron powders to avoid unacceptable sensory changes. Elemental iron powders are less well absorbed than soluble iron compounds and they vary widely in their absorption depending on manufacturing method and physicochemical characteristics. Costs vary with powder type, but elemental iron powders are generally less expensive than ferrous sulfate. This review evaluates the usefulness of the different elemental iron powders based on results from in vitro studies, rat assays, human bioavailability studies, and efficacy studies monitoring iron status in human subjects. It concludes that, at the present time, only electrolytic iron powder can be recommended as an iron fortificant. Because it is only approximately half as well absorbed as ferrous sulfate, it should be added to provide double the amount of iron.

The relative bioavailability in humans of elemental iron powders for use in food fortification.

BACKGROUND: Bioavailability data in humans of elemental iron powders is limited although elemental iron is a common form of iron when used as a fortificant. AIM OF THE STUDY: The relative bioavailability (RBV) of seven elemental iron powders, five commercially available and two developmental are evaluated. In addition, one commercial electrolytic iron powder given with ascorbic acid (AA) was examined. METHODS: Based on a validated method this double-blinded randomized crossover study included three groups of male blood donors (n = 3*16) who were served rolls fortified with different elemental iron powders or ferrous sulfate (FeSO(4)) nine weeks apart. Blood samples were drawn every hour for six hours. RBV was obtained by comparing the increase in serum iron concentration induced by the elemental iron with the increase induced by FeSO(4). RESULTS: All elemental iron powders studied were significantly less well absorbed compared to FeSO(4). The electrolytic iron given with 50-mg AA was as well absorbed as FeSO(4) (molar ratio = 1:6, AA:Fe). The mean RBVs of the iron powders were: electrolytic (A-131, RBV = 0.65); electrolytic (Electrolytic, RBV = 0.59); carbonyl (Ferronyl, RBV = 0.58); H-reduced (AC- 325, RBV = 0.56); H-reduced (Hi-Sol, RBV = 0.50); carbonyl (CF, RBV = 0.37); reduced (Atomet 95SP, RBV = 0.36). The reduced iron was distinguished by having significantly lower RBV (0.36) although no significant overall ranking was possible. CONCLUSION: Based on a validated method this doubleblinded cross-over study in humans showed that the evaluated elemental iron powders currently available for commercial use are significantly less well absorbed compared to FeSO(4). The results indicate that the reduced iron powder was absorbed to a lower extent compared to the other iron powders and only 36% compared to FeSO(4). Ascorbic acid seems to improve the bioavailability of elemental iron even though a rather low molar ratio is used. Thus, if confirmed, this enhancing effect of ascorbic acid on elemental iron when used as a fortificant could be used by co-fortifying them.

Perspectives on iron absorption.

Newly established relationships between dietary iron absorption and serum ferritin and between serum ferritin and iron stores permit calculation of amounts of stored iron under different conditions at steady states when absorption equals losses. The rate of growth of stores can also be calculated. All calculations are based on observations and require no model assumptions. Present analyses demonstrated an effective control of iron absorption preventing development of iron overload in otherwise healthy subjects even if the diet is fortified with iron and even if meat intake is high. There are strong relationships between iron requirements, bioavailability of dietary iron, and amounts of stored iron. Our observations that a reduction in iron stores and a calculated decrease of hemoglobin iron had the same increasing effect on iron absorption suggest that the control of iron absorption is mediated from a common cell, which may register both size of iron stores and hemoglobin iron deficit. We suggest that the hepatocyte is that cell. Nutritional iron deficiency is especially critical in menstruating women, in the latter third of pregnancy, during adolescence for both girls and boys, and in the weaning period from 4 to 6 months to 2 years of age. The body possesses remarkable, potential control systems of probable very ancient origin capable of preventing both iron deficiency and iron overload. Present problems with iron deficiency being the most frequent deficiency disorder are related to nonbiological changes in our societies over the most recent 10,000 years. This perspective on iron homeostasis or iron balance is mainly based on studies in humans of clinical and epidemiological observations, trying to understand why iron deficiency is the most frequent deficiency disorder in the world in spite of the ingenious mechanisms in the body that should prevent it. Withdrawal of iron fortification of flour in Sweden in 1994 led to a significant increase in iron deficiency (defined as serum ferritin < 16 g/L) in 15- to 16-year-old girls examined, from 39.3 to 50.4%, and after elimination of possible confounding factors such as effect of common infections. Addition of powdered red meat to weaning foods increased iron absorption three times and up to the level required to meet the high iron requirements during weaning.

The validation of using serum iron increase to measure iron absorption in human subjects.

The objectives of the present study were to study the correlation between the change in serum Fe and Fe absorption when administering 100 mg Fe (as FeSO4) orally, and to study the correlation between the absorption from a 3 mg and a 100 mg Fe (as FeSO4) dose. The study was conducted in a group of eleven male blood donors, without any evident infection, who had given blood 8 weeks before the study. On three consecutive mornings the subjects were served a wheat roll fortified with Fe. On the first 2 d the roll was fortified with 3 mg Fe labelled with 59Fe; on day 3 the roll was fortified with 100 mg Fe labelled with 55Fe. The serum Fe response to the 100 mg dose was followed for 6 h. Fe absorption was measured by whole-body counting. High correlations were seen between the absorption of Fe and the change in serum Fe after 100 mg Fe (r2 0.94, P<0.001), between the absorption from 3 mg and 100 mg Fe (r2 0.88, P<0.001), and between the absorption from 3 mg Fe and change in serum Fe after 100 mg Fe (r2 0.90, P<0.001). This strengthens the evidence that it is possible to use the change in serum Fe as a measure of Fe absorption, e.g. when establishing the relative bioavailability for Fe powders. The results also imply that the induced serum Fe increase following 100 mg Fe added to a food could predict the Fe absorption of a small dose of Fe added to the same meal.

The role of meat to improve the critical iron balance during weaning.

BACKGROUND: Iron requirements during the weaning period are the highest per unit body weight during human life, and diet is often insufficient to cover iron needs. For the first time in infant nutrition the absorption of both nonheme and heme iron from a typical weaning gruel after addition of meat with and without ascorbic acid (AA) to improve bioavailability was studied. METHODS: Nonheme and heme iron absorption from gruel was measured in 33 adults using 2 radioiron isotopes--an inorganic iron salt to label nonheme iron, the other biosynthetically labeled rabbit hemoglobin to label heme iron. Iron absorption was measured from the basal gruel (based on milkpowder and cereals) and from basal gruel added 20 g red powdered meat, alone and together with 20 mg AA in 4 different trials. RESULTS: Nonheme iron absorption from the basal meal was 0.33 mg/1000 kcal and the increase from added 20 mg AA was 39%, whereas addition of red meat increased nonheme iron absorption by 85%. This latter increase was unexpectedly high. Total iron absorption was further increased by heme iron absorption of 0.23 mg Fe/1000 kcal. When adding both meat and AA, total iron absorption amounted to 1.08 mg iron/1000 kcal, ie, exceeding 1 mg/1000 kcal, a level estimated to correspond with daily iron requirements in 95% of infants aged 12 months. CONCLUSIONS: Addition of powdered red meat to weaning gruels markedly increased total iron absorption. A weaning diet with added powdered meat and AA may serve as a viable option to satisfy the body's high iron requirements during this critical period.