The Evidence for Estimating the Recommended Nutrient Intake for Iron

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

68. Hallberg, L. 1995. Iron balance in menstruating women. Eur. J. Clin. Nutr., 49: 200-207.

69. Hallberg L., Hulthén L. & Garby L. 1998. Iron stores in man in relation to diet and iron requirements. Eur. J. Clin. Nutr., 52: 623-31.

70. Hallberg, L. 1993. Screening for iron deficiency: an analysis based on bone-marrow examinations and serum ferritin determinations in a population sample of women. Br. J. Haematol., 85: 787-798. 

To translate physiologic iron requirements, given in Table 30, into dietary iron requirements, the bio-availability of iron in different diets must be calculated. It is therefore necessary to choose an iron status where the supply of iron to the erythrocyte precursors and other tissues starts to be compromised. A state of iron-deficient erythropoiesis occurs when iron can no longer be mobilised from iron stores; iron can no longer be mobilised when stores are almost completely empty. A reduction then occurs, for example, in the concentration of haemoglobin and in the average content of haemoglobin in the erythrocytes (a reduction in meancorpuscular haemoglobin). At the same time the concentration of transferrin in the plasma increases because of an insufficient supply of iron to liver cells. These changes were recently shown to occur rather suddenly at a level of serum ferritin of ≤15 μg/l (68, 70).

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

98. Rossander, L., Hallberg, L. & Björn-Rasmussen, E. 1979. Absorption of iron from breakfast meals. Am. J. Clin. Nutr., 32: 2484-2489.

99. Hallberg, L. & Rossander, L. 1982. Bio-availability of iron from Western-type whole meals. Scand. J. Gastroenterol., 17: 151-160.

A continued negative iron balance will further reduce the level of haemoglobin. Symptoms related to iron deficiency are less related to the haemoglobin level and more to the fact that there is a compromised supply of iron to tissues. The bio-availability of iron in meals consumed in countries with a Western-type diet has been measured by using different methods. Numerous single-meal studies have shown absorption of non-heme iron ranging from 5 percent to 40 percent (59, 98, 99).

19. Hallberg, L. & Rossander-Hulthénm, L. 1991. Iron requirements in menstruating women. Am. J. Clin. Nutr., 54: 1047-1058. 

Attempts have also been made to estimate the bio-availability of dietary iron in populations consuming Western-type diets by using indirect methods (e.g., calculation of the coverage of iron requirements in groups of subjects with known dietary intake). Such estimations suggest that in borderline iron-deficient subjects the bio-availability from good diets may reach a level around 14–16 percent (15 percent relates to subjects who have a serum ferritin value of <15μg/l or a reference dose absorption of 56.5 percent) (19).

22. Hallberg, L., Hulthén, L. & Gramatkovski, E. 1997. Iron absorption from the whole diet in men: how effective is the regulation of iron absorption? Am. J. Clin. Nutr., 66: 347-56.

43. Gleerup, A. 1995. Iron absorption from the whole diet: comparison of the effect of two different distributions of daily calcium intake. Am. J. Clin. Nutr., 61: 97-104.

60. Hulthén, L. 1995. Iron absorption from the whole diet. Relation to meal composition, iron requirements and iron stores. Eur. J. Clin. Nutr., 49: 794-808.

Recently, direct measurements were made of the average bio-availability of iron in different Western-type diets (22, 43, 60).

Expressed as total amounts of iron absorbed from the whole diet, it was found that 53.2 μg Fe/kg/day could be absorbed daily from each of the two main meals of an experimental diet which included ample amounts of meat or fish. For a body weight of 55 kg and an iron intake of 14 mg/day, this corresponds to a bio-availability of 21 percent in subjects with no iron stores and an iron-deficient erythropoiesis. A diet common among women in Sweden contained smaller portions of meat and fish, higher phytates, and some vegetarian meals each week was found to have a bio-availability of 12 percent. Reducing the intake of meat and fish further will reduce the bio-availability to about 10 percent (25μg Fe/kg/day). 

In vegetarians the bio-availability is usually low because of the absence of meat and fish and a high intake of phytate and polyphenols. An average good Western-type whole diet has a bio-availability of about 15 percent but for common diets, especially among women, the bio-availability is around 12 percent or even 10 percent. In countries or for certain groups in a population with a very high meat intake, the bioavailability may rather be around 18 percent.

38. Morck, T.A., Lynch, S.E. & Cook, J.D. 1983. Inhibition of food iron absorption by coffee. Am. J. Clin. Nutr., 37: 416-420.

In Western countries, a high bio-availability is mainly associated with a high meat intake, a high intake of ascorbic acid with meals, a low intake of phytate-rich cereals, and no coffee or tea within 2 hours of the main meals (38). Table 43 shows examples of diets with different iron bio-availability.