Bioavailability of Fortified Iron

A list of iron sources that are generally recognized as safe (GRAS) by the US Food and Drug Administration (FDA) is given in Table 3. However, as shown in Table 4, the bioavailability of different iron sources varies widely. Moreover, even within a given source of iron, such as the elemental iron powders commonly used to fortify various ready-to-eat breakfast cereals and other products, a significant disparity (5-148%) in relative bioavailability (compared to ferrous sulfate) can be observed. To some extent, these differing bio-availability estimates reflect the influence of the characteristics of the fortified product in terms of its contribution of various enhancers or inhibitors (Table 1) on iron bioavailability. In addition, other factors also can affect the bioavailability of elemental iron powders, such as the particle size of the fortificant

Table 3 Iron and zinc compounds listed as generally recognized as safe by the US Food and Drug Administration

Iron compounds

Zinc compounds

Elemental iron Ferrous ascorbate Ferrous carbonate Ferrous citrate Ferrous fumarate Ferrous gluconate Ferrous lactate Ferrous sulfate Ferric ammonium citrate Ferric chloride Ferric citrate Ferric pyrophosphate Ferric sulfate

Zinc sulfate Zinc chloride Zinc gluconate Zinc oxide Zinc stearate compound - a finer particle size is associated with greater iron bioavailability.

There is very limited information available concerning the bioavailability of calcium or other nutrients added as a fortificant to various products. One study in elderly women found that calcium citrate malate used to fortify orange juice had equivalent bioavailability to calcium from milk or calcium from a calcium carbonate supplement. In a study with adult subjects, the

Table 4 Average relative bioavailability in humans of various iron sources used as iron fortification compounds

Average relative

Iron compound

Approximate

bioavailability

iron content

(%)

>90% group

106a

Ferrous lactate

19

100

Ferrous sulfate 7H2O

20

100

Ferrous fumarate

33

92

Ferrous succinate

35

>60-<90% group

89

Ferrous gluconate

12

75

Electrolytic elemental

97

Fe powders

74

Ferric saccharate

10

74

Ferrous citrate

24

62

Ferrous tartrate

22

Variable (%)

21-74

Ferric pyrophosphate

25

25-32

Ferric orthophosphate

28

13-148

H-reduced elemental

97

Fe powder

5-20

Carbonyl elemental Fe

99

powder

aRelative to absorption of iron from ferrous sulfate = 100% Adapted from Lynch S (2002) Food iron absorption and its importance for the design of food fortification strategies. Nutrition Reviews 60: S3-S15.

bioavailability of a single 25 000IU dose of vitamin D2 was assessed from whole milk, skim milk, and vitamin D-fortified oil given with toast. No difference in peak serum vitamin D2 was found following these three treatments, suggesting that the fat content of whole milk does not influence vitamin D bioavailability. It has also been shown that consumption of vitamin D-fortified orange juice (1000IU/240ml) for 12 weeks significantly increased serum 25-hydroxyvitamin D concentrations.

Fat content of a meal may have an important effect on carotenoid bioavailability. The absorption of carotenoids (a-carotene, ^-carotene, and lycopene) from salad vegetables was found to be undetectable if a fat-free salad dressing was used, but substantially greater absorption occurred with a full-fat salad dressing. The amount of fat needed to promote optimal absorption of vitamin E and carotenoids may be rather limited. No difference in absorption of vitamin E and a- or ^-carotene was observed when supplements were administered with either 3g or 36 g of dietary fat. In contrast, lutein ester absorption was more than twice as great when consumed with the higher fat level.

Bioavailability of food sources of folate are usually only about 50% of synthetic folic acid. This systematic difference may be due to the occurrence of polyglutamyl folic acid in foods that reduce folate absorption.

See also: Calcium. Carotenoids: Chemistry, Sources and Physiology. Cobalamins. Copper. Food Fortification: Developed Countries; Developing Countries. Iodine: Physiology, Dietary Sources and Requirements. Microbiota of the Intestine: Prebiotics. Osteoporosis. Selenium. Vitamin A: Biochemistry and Physiological Role. Zinc: Physiology.

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