Enhancement of Iron Absorption

Reference from the joint report of FAO/WHO expert consultation on Human Vitamins and Minerals verbatim.

34. Siegenberg, D. 1991. Ascorbic acid prevents the dose-dependent inhibitory effects of polyphenols and phytates on nonheme-iron absorption. Am. J. Clin. Nutr., 53: 537-41.

51. Cook, J.D. & Monsen, E.R. 1977. Vitamin C, the common cold and iron absorption. Am. J. Clin. Nutr., 30: 235-241.

52. Hallberg, L., Brune, M. & Rossander, L. 1986. Effect of ascorbic acid on iron absorption from different types of meals. Studies with ascorbic-acid-rich foods and synthetic ascorbic acid given in different amounts with different meals. Hum. Nutr: Appl. Nutr., 40: 97-113.

53. Derman, D.P. 1980. Importance of ascorbic acid in the absorption of iron from infant foods. Scand. J. Haematol., 25: 193-201.

54. Hallberg, L., Brune, M. & Rossander-Hultén, L-S. 1987. Is there a physiological role of vitamin C in iron absorption? Ann. York. Acad. Sci., 498: 324-332.

Ascorbic acid is the most potent enhancer of non-heme iron absorption (34, 51-53). Synthetic vitamin C increases the absorption of iron to the same extent as the native ascorbic acid in fruits, vegetables, and juices. The effect of ascorbic acid on iron absorption is so marked and essential that this effect could be considered as one of vitamin C’s physiologic roles (54).

55. Layrisse, M., Martinez-Torres, C. & Roch, M. 1968. The effect of interaction of various foods on iron absorption. Am. J. Clin. Nutr., 21: 1175-1183.

56. Layrisse, M. 1969. Food iron absorption: A comparison of vegetable and animal foods.

Blood, 33: 430-443.

57. Cook, J.D. & Monsen, E.R. 1976. Food iron absorption in Human subjects. III. Comparison of the effect of animal proteins on nonheme iron absorption. Am. J. Clin. Nutr., 29: 859-867.

58. Björn-Rasmussen, E. & Hallberg, L. 1979. Effect of animal proteins on the absorption of food iron in man. Nutr. Metab., 23: 192-202.

Each meal should preferably contain at least 25 mg of ascorbic acid and possibly more if the meal contains many inhibitors of iron absorption. Therefore, a requirement of ascorbic acid for iron absorption should be taken into account when establishing the requirements for vitamin C, that are set only to prevent vitamin C deficiency (especially scurvy). Meat, fish, and seafood all promote the absorption of non-heme iron (55-58).

21. Hallberg, L. 1979. Dietary heme iron absorption. A discussion of possible mechanisms for the absorption-promoting effect of meat and for the regulation of iron absorption. Scand. J. Gastroenterol., 14: 769-779.

29. Gillooly, M. 1983. The effect of organic acids, phytates and polyphenols on absorption of iron from vegetables. Br. J. Nutr., 49: 331-342.

The mechanism for this effect has not been determined. It should be pointed out that meat also enhances the absorption of heme iron to about the same extent (21). Meat promotes iron nutrition in two ways: it stimulates the absorption of both heme and non-heme iron and it provides the well-absorbed heme iron. Epidemiologically, the intake of meat has been found to be associated with a lower prevalence of iron deficiency. Organic acids, such as citric acid, have in some studies been found to enhance the absorption of non-heme iron (29).

47. Hallberg, L. & Rossander, L. 1984. Improvment of iron nutrition in developing countries: comparison of adding meat, soy protein, ascorbic acid, citric acid, and ferrous sulphate on iron absorption from a simple Latin American-type of meal. Am. J. Clin.

Nutr., 39: 577-583.

52. Hallberg, L., Brune, M. & Rossander, L. 1986. Effect of ascorbic acid on iron absorption from different types of meals. Studies with ascorbic-acid-rich foods and synthetic ascorbic acid given in different amounts with different meals. Hum. Nutr: Appl. Nutr., 40: 97-113.

59. Hallberg, L. & Rossander, L. 1982. Absorption of iron from Western-type lunch and dinner meals. Am. J. Clin. Nutr., 35: 502-509.

49. Baynes, R.D. 1990. The promotive effect of soy sauce on iron absorption in Human subjects. Eur. J. Clin. Nutr., 44: 419-24.

50. Macfarlane, B.J. 1990. The effect of traditional oriental soy products on iron absorption. Am. J. Clin. Nutr., 51: 873-80.

This effect is not observed as consistently as is the effect of ascorbic acid (47, 52). Sauerkraut (59) and other fermented vegetables and even some fermented soy sauces (49, 50) enhance iron absorption. The nature of this enhancement has not yet been determined.

Iron absorption from meals

24. Hallberg, L. 1974. The pool concept in food iron absorption and some of its implications. Proc. Nutr. Soc., 33: 285-291.

The pool concept in iron absorption implies that there are two main pools in the gastrointestinal lumen – one pool of heme iron and another pool of non-heme iron – and that iron absorption takes place independently from these two pools (24).

 20. Hallberg, L. 1981. Bio-availability of dietary iron in man. Ann. Rev. Nutr., 1: 123-147. 

The pool concept also implies that the absorption of iron from the non-heme iron pool results from all ligands present in the mixture of foods included in a meal. The absorption of non-heme iron from a certain meal not only depends on its iron content but also, and to a marked degree, on the composition of the meal (i.e., the balance among all factors enhancing and inhibiting the absorption of iron). The bio-availability can vary more than 10-fold among meals with a similar content of iron, energy, protein, fat, etc. (20).

Just the addition of certain spices (e.g., oregano) or a cup of tea may reduce the bio-availability by one-half or more. However, the addition of certain vegetables or fruits containing ascorbic acid may double or even triple iron absorption, depending on the other properties of the meal and the amounts of ascorbic acid present.