This page features 12 unique references to scientific papers.

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Scientific Research

1Nutrient-Nutrient Interactions

1.1. Chelation

Several plant-derived compounds have the ability to reduce iron absorption secondary to forming bonds with the iron molecule and sequestering it in the intestines, and coingestion of these compounds with iron reduces the efficacy of iron supplementation.

Curcumin (the most active component of turmeric) has shown this potential in mice only when high doses of curcumin (estimated human dose of 8-12g) are paired with low dietary iron levels;[1] diets with adequate levels of iron not being significantly hindered[1] and dietary turmeric at 500mg not having any effect in humans.[2]

The addition of 4.2g ground chili (capsicum annuum) to a meal fortified with 4mg non-heme iron showed a moderate inhibitory effect on iron absorption by 38%; this test meal being relatively high in phytic acid due to the addition of chili.[2] Rosemary (source of rosmarinic acid) has also been noted to reduce nonheme iron absorption.[3]

In regards to spices, those with high phenolic contents or those with a high phytate content may reduce iron absorption when both are ingested at the same time

Psyllium is a dietary fiber comprised of roughly equal parts soluble and insoluble fiber. While one study has noted a reduction in iron accumulation when coingested with non-heme iron[4] while other studies using prolonged supplementation of around 10g fail to find alterations in iron metabolism.[5][6][7] Psyllium has the potential to both reduce absorption of minerals via direct binding to nonheme in a manner not influenced by Vitamin C[8] while in the colon the increase in pH from psyllium has been noted to increase resorption of calcium;[9] thought to apply to other minerals as well.

While there may be an acute inhibitory effect on dietary fibers on nonheme iron absorption, the long term relevance of this is not known since fermentable dietary fibers may also increase mineral resorption from the colon

Coffee is known to inhibit iron absorption when coingested with nonheme iron,[10] potentially due to the activities of chlorogenic acid which is a known iron chelator[11] which would extend this inhibition to the dietary supplement known as Green coffee extract (a higher source of chlorogenic acid).

Other beverages that have been noted to inhibit iron absorption in a test meal include peppermint tea,[10] green tea (due to catechins[3]), black tea[10] (additional theaflavin component may play a role[12]), vervain tea,[10] lime flower tea,[10] pennyroyal tea,[10] and chamomile tea.[10]

A wide variety of beverages that are known to have a high antioxidant content, including coffee and teas from camellia sinensis such as green or black teas have some acute inhibitory effect on iron absorption

Scientific Support & Reference Citations


  1. Jiao Y1, et al Curcumin, a cancer chemopreventive and chemotherapeutic agent, is a biologically active iron chelator . Blood. (2009)
  2. Tuntipopipat S1, et al Chili, but not turmeric, inhibits iron absorption in young women from an iron-fortified composite meal . J Nutr. (2006)
  3. Samman S1, et al Green tea or rosemary extract added to foods reduces nonheme-iron absorption . Am J Clin Nutr. (2001)
  4. Rossander L Effect of dietary fiber on iron absorption in man . Scand J Gastroenterol Suppl. (1987)
  5. Bell LP1, et al Cholesterol-lowering effects of soluble-fiber cereals as part of a prudent diet for patients with mild to moderate hypercholesterolemia . Am J Clin Nutr. (1990)
  6. Dennison BA1, Levine DM Randomized, double-blind, placebo-controlled, two-period crossover clinical trial of psyllium fiber in children with hypercholesterolemia . J Pediatr. (1993)
  7. Anderson JW1, et al Cholesterol-lowering effects of psyllium hydrophilic mucilloid for hypercholesterolemic men . Arch Intern Med. (1988)
  8. Fernandez R, Phillips SF Components of fiber bind iron in vitro . Am J Clin Nutr. (1982)
  9. Trinidad TP1, Wolever TM, Thompson LU Availability of calcium for absorption in the small intestine and colon from diets containing available and unavailable carbohydrates: an in vitro assessment . Int J Food Sci Nutr. (1996)
  10. Hurrell RF1, Reddy M, Cook JD Inhibition of non-haem iron absorption in man by polyphenolic-containing beverages . Br J Nutr. (1999)
  11. Kono Y1, et al Iron chelation by chlorogenic acid as a natural antioxidant . Biosci Biotechnol Biochem. (1998)
  12. O'Coinceanainn M1, et al Reaction of iron(III) with theaflavin: complexation and oxidative products . J Inorg Biochem. (2004)