Solubility Inhibitors Of Nonhaem Iron

• Polyphenols, including tannin derivatives of gallic acid (tea has been reported to reduce iron absorption by 60%, coffee by 40%) (Kaltwasser et al 1998, Morck et al 1983). A number of studies have shown that tea catechins can inhibit intestinal non-haem iron absorption (Ullmann et al 2005); however, polyphenols do not have chelating effects on cooked haem iron (Breet et al 2005). Recent studies suggest that impaired absorption is unlikely to be significant in people with normal iron stores (Breet et al 2005, Ullmann et al 2005). The addition of milk to tea may reduce the chelating effects.

• Oxalic acid (spinach, chard, chocolate, berries).

• Calcium — single-meal studies have established that calcium (including calcium phosphate and foods such as milk) reduces iron absorption by up to 70% (Hallberg et al 1991); however, the effect may not be as pronounced when calcium is served as part of a whole diet. For instance, the consumption of a glass of milk or the equivalent amount of calcium from fortified food does not appear to decrease non-haem iron absorption (Grinder-Pedersen et al 2004). Although it remains to be shown in iron-deficient persons, long-term iron status does not seem to be compromised by high calcium intake (Molgaard et al 2005).

• Zinc competes with iron for absorption (Solomons 1983) — inorganic zinc supplements may reduce iron absorption by 66-80% (Crofton et al 1989), and supplements containing both iron and zinc may not be as efficacious as the same doses given in isolation (Fischer Walker et al 2005, Lind et al 2003), but nutrients consumed in a meal may not be as affected (Whittaker 1998).

• Manganese may reduce absorption by 22-40% (Rossander-Hulten 1991).

• Rapid intestinal transit time.

• Malabsorption syndromes.

• Helicobacter pylori infection (Ciacci et al 2004).

• Gastrointestinal blood loss (Higgins & Rockey 2003).

• Insufficient digestive secretions (including achlorhydria).

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