Iron absorption inhibitors
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Iron Absorption Inhibitors: Key Dietary Compounds
Iron absorption in the human gut is influenced by several dietary inhibitors, which can significantly reduce the amount of iron the body takes up from food. Understanding these inhibitors is important for both managing iron deficiency and conditions of iron overload.
Phytates and Inositol Phosphates as Iron Absorption Inhibitors
Phytates, found in cereals and legumes, are among the most potent inhibitors of iron absorption. The inhibitory effect is dose-dependent: even small amounts can reduce iron uptake, with higher doses causing up to 82% reduction in absorption. This effect is primarily due to the ability of phytates to bind iron, making it unavailable for absorption in the gut 345. Inositol hexaphosphate (IP6) and its less-phosphorylated forms (IP5, IP4, IP3) also inhibit iron absorption, with IP5 showing a clear inhibitory effect. While IP3 and IP4 alone do not significantly inhibit iron absorption, they can contribute to inhibition when present in processed foods, likely by binding iron in combination with other inositol phosphates .
Polyphenols and Tannins: Tea, Coffee, and Plant Foods
Polyphenols, especially tannins found in tea and coffee, are strong inhibitors of nonheme iron absorption. Tea can reduce iron absorption by 41–95%, and coffee by up to 39%, with the effect being concentration-dependent 48910. The timing of tea or coffee consumption matters: drinking tea or coffee with a meal has a much stronger inhibitory effect than consuming them an hour before or after eating. For example, waiting one hour after a meal before drinking tea can reduce its inhibitory effect by about half 810.
Minerals: Manganese and Zinc
Manganese can directly compete with iron for absorption pathways in the gut, significantly reducing iron uptake when present in high amounts. Zinc, on the other hand, only inhibits iron absorption when present in large excess and in solution, but not when consumed as part of a meal, suggesting different absorption mechanisms for zinc and iron .
Dietary Proteins and Calcium
Proteins from soybeans, milk, and eggs, as well as calcium, are also known to inhibit iron absorption. These effects are significant enough to be considered when planning diets for individuals at risk of iron deficiency or those needing to limit iron uptake, such as patients with genetic haemochromatosis .
Counteracting Iron Absorption Inhibitors
Role of Ascorbic Acid (Vitamin C)
Ascorbic acid is a powerful promoter of iron absorption and can counteract the inhibitory effects of phytates and polyphenols. Adding vitamin C to meals can restore iron absorption even in the presence of high levels of these inhibitors 34.
Role of Vitamin A
Vitamin A can also overcome the inhibitory effects of both polyphenols (from tea and coffee) and phytates. It appears to do this by forming a complex with iron during digestion, keeping it soluble and available for absorption .
Conclusion
Iron absorption inhibitors in the diet include phytates, polyphenols (from tea and coffee), certain minerals (like manganese), and some dietary proteins and calcium. Their effects are often dose-dependent and can be influenced by meal composition and timing. However, the negative impact of these inhibitors can be mitigated by consuming vitamin C or vitamin A with iron-rich meals. Understanding these interactions is crucial for optimizing iron nutrition and managing conditions related to iron metabolism 12345689+1 MORE.
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