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Clinical Studies (Return to Clinical
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VITAMIN C ENHANCES
IRON ADSORPTION
Atanassova
B.D., Tzatchev KN (2008). Ascorbic acid--important for iron metabolism. Folia Med ( Plovdiv). Oct-Dec; 50(4):11-6.
Ascorbic acid is actively
involved in the control of iron metabolism. It has long been known to enhance absorption of iron
from test meals. At first this effect was ascribed to luminal reduction and solubilsation of
iron. Later, molecular cloning of mammalian duodenal brush-border reductase activity and studies
in animals and man strongly supported ascorbate as the intracellular electron donor for duodenal
ferri-reductase activity and provided molecular mechanism for an intracellular role of ascorbate
in intestinal iron absorption. Factors that alter duodenal ascorbate levels (dietary intake of
ascorbate, dehydroascorbate, or oxidants) may therefore alter the rate of absorption. Ascorbate
could play dual role in human cells; it could react as pro-oxidant and as antioxidant. The
balance of these contradictory effects depends on ascorbate concentration. Pro-oxidant reactions
predominate at low concentrations; at higher concentrations vitamin C reacts as antioxidant. The
increase of plasma ascorbate in human iron deficiency, especially in females in active age,
could explain gender-related biological variation of plasma levels of vitamin C. The possible
participation of ferric reductase activity Dcytb in transferrin cycle in liver and in neutrophil
host defense implies new aspects of the role of vitamin C in the regulation of iron
homeostasis.
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Teucher B, Olivares M, Cori H
(2004). Enhancers of iron absorption: ascorbic acid and other organic acids
. Int J Vitam Nutr Res. Nov;
74(6):403-19.
Ascorbic acid (AA), with its
reducing and chelating properties, is the most efficient enhancer of non-heme iron absorption
when its stability in the food vehicle is ensured. The number of studies investigating the
effect of AA on ferrous sulfate absorption far outweighs that of other iron fortificants. The
promotion of iron absorption in the presence of AA is more pronounced in meals containing
inhibitors of iron absorption. Meals containing low to medium levels of inhibitors require the
addition of AA at a molar ratio of 2:1 (e.g., 20 mg AA: 3 mg iron). To promote absorption in the
presence of high levels of inhibitors, AA needs to be added at a molar ratio in excess of 4:1,
which may be impractical. The effectiveness of AA in promoting absorption from less soluble
compounds, such as ferrous fumarate and elemental iron, requires further investigation. The
instability of AA during food processing, storage, and cooking, and the possibility of unwanted
sensory changes limits the number of suitable food vehicles for AA, whether used as vitamin
fortificant or as an iron enhancer. Suitable vehicles include dry-blended foods, such as
complementary, precooked cereal-based infant foods, powdered milk, and other dry beverage
products made for reconstitution that are packaged, stored, and prepared in a way that maximizes
retention of this vitamin. The consumption of natural sources of Vitamin C (fruits and
vegetables) with iron-fortified dry blended foods is also recommended. Encapsulation can
mitigate some of the AA losses during processing and storage, but these interventions will also
add cost. In addition, the bioavailability of encapsulated iron in the presence/absence of AA
will need careful assessment in human clinical trials. The long-term effect of high AA intake on
iron status may be less than predicted from single meal studies. The hypothesis that an overall
increase of dietary AA intake, or fortification of some foods commonly consumed with the main
meal with AA alone, may be as effective as the fortification of the same food vehicle with AA
and iron, merits further investigation. This must involve the consideration of practicalities of
implementation. To date, programs based on iron and AA fortification of infant formulas and
cow's milk provide the strongest evidence for the efficacy of AA fortification. Present results
suggest that the effect of organic acids, as measured by in vitro and in vivo methods, is
dependent on the source of iron, the type and concentration of organic acid, pH, processing
methods, and the food matrix. The iron absorption-enhancing effect of AA is more potent than
that of other organic acids due to its ability to reduce ferric to ferrous iron. Based on the
limited data available, other organic acids may only be effective at ratios of acid to iron in
excess of 100 molar. This would translate into the minimum presence/addition of 1 g citric acid
to a meal containing 3 mg iron. Further characterization of the effectiveness of various organic
acids in promoting iron absorption is required, in particular with respect to the optimal molar
ratio of organic acid to iron, and associated feasibility for food application purposes. The
suggested amount of any organic acid required to produce a nutritional benefit will result in
unwanted organoleptic changes in most foods, thus limiting its application to a small number of
food vehicles (e.g., condiments, beverages). However, fermented foods that already contain high
levels of organic acid may be suitable iron fortification vehicles.
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