• plant-based sources of iron (e.g., green leafy vegetables), and
• foods rich in vitamin C (which can triple the bioavailability of iron)
Today, many people around the world are iron deficient. They can
improve their iron status by changing their diets. But how does this
work? Here is an overview of iron absorption--the factors that enhance
it and the substances that inhibit it.
Heme versus nonheme iron
The bioavailability of iron depends on several factors. People who
are iron-replete absorb iron less easily than people who are
In addition, absorption depends on the specific form that iron takes.
Heme iron is the most readily absorbed form of iron, and it’s found
in shellfish, red meat, poultry, and fish (see the chart in this article
about iron rich goods). On average, people absorb between 15-35% of the
heme iron they consume (Insel et al 2003).
Nonheme iron is found in plant foods, as well as in eggs, milk, and meat.
Compared with heme iron, it’s less easily absorbed by the body.
Moreover, sources of nonheme iron often contain phytates, which
bind to iron and carry it through the digestive tract unabsorbed.
As a result, the foods with high iron content aren’t necessarily
the best sources of iron. By weight, soybeans have roughly twice the
iron of beef. But only about 7% of the iron in soybeans is absorbed.
Spinach is also high in iron, but less than 2% of the iron in cooked
spinach is absorbed (Scrimshaw 1991).
Iron absorption enhancers
Nonheme iron is harder to absorb. But this doesn’t mean it’s
unimportant. What’s needed is a way to improve the body's absorption of
nonheme iron, and you can do this by adding one or more of these iron
absorption enhancers to your meals:
• Vitamin C (Teucher et al 2004; Fidler et al 2009)
• Beef (Johnson and Walker 1992; Englemann et al 1998)
• Poultry (Hurrell et al 2006)
• Salmon (and, presumably, some other kinds of fish: Navas-Carretero et al 2008)
• Pork (Engle-Stone et al 2005)
• Citric acid (Hallberg and Rossander 1984)
How much difference do these additives make?
Vitamin C may be particularly effective. One study reported that adding just 63 mg of vitamin C to a
meal rich in nonheme iron yielded a 2.9-fold increase in iron absorption
(Fidler et al 2009).
Meat can also make a big difference. Experiments suggest that
adding 50 to 85 grams of meat to a meal results in a 1.5- to 4-fold
increase in iron absorption (Baech 2003; Baynes and Bothwell 1990; Cook
et al 1976; Engle-Stone et al 2005; Navas-Carretero 2008).
Beef may more effective than other meats. In one experiment, beef
protein enhanced iron absorption 80% better than did chicken protein
(Hurrell et al 2006).
Iron absorption inhibitors
The flip side of the coin are substances that inhibit the absorption of iron:
• phytic acid (found in grains, legumes, and other plant foods)
• egg protein (from both the white and the yolk)
• minerals that compete with iron for absorption: calcium, zinc, magnesium, and copper
• tannic acid (in tea)
• certain herbs, including peppermint and chamomile
Notice that many nutritious, healthful foods contain iron
absorption inhibitors. It’s not desirable to cut these out of your
child’s diet--your child needs calcium, zinc, phosphorus, and fiber.
However, if your child is iron deficient, it might be helpful to
avoid some of these foods just before, during, or after a meal that
contains iron rich foods.
For instance, experiments have demonstrated that people absorb
much less iron from bread when their meals include egg protein, tea,
peppermint, chamomile, or coffee (Hurrell et al 1999; Hurrell et al
Similar experiments have demonstrated that calcium interferes with the absorption of iron (Hallberg 1998; Perales et al 2006).
What about phytic acid? Phytates, which are found in most plant
foods, can reduce iron absorption by up to 80%. But vitamin C—consumed
along with a meal--can counteract the effect. In one study, preschoolers
with iron deficiency anemia were given vitamin C supplements twice a
day—100 mg at each of two phytate-rich meals. After two months, most of
the kids were no longer anemic (Seshahdri et al 1985).
This underscores the importance of vitamin C. Many grains and legumes (including soy) can be good sources of iron--if you consume them with vitamin C.
Iron-fortified foods really can help. Iron-fortified
cereals--consumed with vitamin C--can be an effective way to improve
your child’s iron status. So can iron-fortified soy sauce (Chen et al
Cooking with iron cookware can add iron to your diet, particularly if you cook acidic foods at high temperatures (Kuligowski and Halperin 1992).
Although egg protein inhibits the absorption of iron, a few egg yolks might not hurt.
In a study of healthy, iron sufficient weanling infants, researchers
fed 6-month-old babies egg yolks from eggs enriched with n-3 fatty
acids. Babies ate 4 cooked yolks a week for 6 months. At the end of the
treatment, their iron status was similar to that of controls (Makrides
et al 2002). The study didn’t describe whether the eggs were eaten alone
or in the context of a meal.
Baech SB, Hansen M, Bukhave K, Jensen M, Sørensen SS, Kristensen L,
Purslow PP, Skibsted LH, and Sandström B. 2003. Nonheme-iron absorption
from a phytate-rich meal is increased by the addition of small amounts
of pork meat. Am J Clin Nutr. 77(1):173-9.
Baynes RD and Bothwell TH. 1990. Iron deficiency. Ann. Rev. Nutr. 10:133-148.
Chen J, Zhao X, Zhang X, Yin S, Piao J, Huo J, Yu B, Qu N, Lu Q,
Wang S, and Chen C. 2005. Studies on the effectiveness of
NaFeEDTA-fortified soy sauce in controlling iron deficiency: a
population-based intervention trial. Food Nutr Bull. 26(2):177-86;
Cook JD and Monsen ER. 1976. Food iron absorption in human
subjects. III. Comparison of the effect of animal proteins on nonheme
iron absorption. Am J Clin Nutr 29:859–67.
Eaton SB, Eaton SB 3rd, and Konner MJ. 1999. Paleolithic
nutrition revisited: a twelve-year retrospective on its nature and
implications" European Journal of Clinical Nutrition 51 (4): 207–16.
Engle-Stone R, Yeung A, Welch R, and Glahn R. 2005. Meat and
ascorbic acid can promote Fe availability from Fe-phytate but not from
Fe-tannic acid complexes. J Agric Food Chem. 28;53(26):10276-84.
Engelmann MD, Davidsson L, Sandström B, Walczyk T, Hurrell RF,
and Michaelsen KF. 1988. The influence of meat on nonheme iron
absorption in infants. Pediatr Res 43:768–73.
Fidler MC, Davidsson L, Zeder C, and Hurrell RF. 2004. Erythorbic
acid is a potent enhancer of nonheme-iron absorption. Am J Clin Nutr.
Hallberg L. 1998. Does calcium interfere with iron absorption? Am. J. Clin. Nutr. 68: 3-4.
Hurrell RF, Reddy MB, Juillerat M, Cook JD. 2006. Meat protein
fractions enhance nonheme iron absorption in humans. J Nutr.
Hurrell RF. 2004. Phytic acid degradation as a means of improving iron absorption. Int J Vitam Nutr Res. 74(6):445-52.
Hurrell RF, Reddy M, Cook JD. 1999. Inhibition of non-haem iron
absorption in man by polyphenolic-containing beverages. Br J Nutr. 1999
Hurrell RF, Lynch SR, Trinidad TP, Dassenko SA, and Cook JD.
1988. Iron absorption in humans: bovine serum albumin compared with beef
muscle and egg white. Am J Clin Nutr 47:102–7.
Insel, PM, Turner RE, and Ross D. 2003. Nutrition. 3rd edition. Jones and Bartlett.
Ishikawa SI, Tamaki S, Arihara K, Itoh M. 2007. Egg yolk protein
and egg yolk phosvitin inhibit calcium, magnesium, and iron absorptions
in rats. J Food Sci. 2007 Aug;72(6):S412-9.
Kollipara UK and Brittin HC. 1996. Increased iron content of some Indian foods due to cookware. J Am Diet Assoc. 96(5):508-10.
Kuligowski J and Halperin KM. 1992. Stainless steel cookware as a
significant source of nickel, chromium, and iron. Arch Environ Contam
Navas-Carretero S, Pérez-Granados AM, Sarriá B, Carbajal A,
Pedrosa MM, Roe MA, Fairweather-Tait SJ, and Vaquero MP. 2008. Oily fish
increases iron bioavailability of a phytate rich meal in young iron
deficient women. J Am Coll Nutr. 27(1):96-101.
Perales S, Barberá R, Lagarda MJ, and Farré R. 2006.
Fortification of milk with calcium: effect on calcium bioavailability
and interactions with iron and zinc. J Agric Food Chem. 2006 Jun
Rutzke CJ, Glahn RP, Rutzke MA, Welch RM, Langhans RW, Albright
LD, Combs GF Jr, and Wheeler RM. 2004. Bioavailability of iron from
spinach using an in vitro/human Caco-2 cell bioassay model. Habitation
Scrimshaw NS. 1991. Iron deficiency. Sci Am. 265(4):46-52.
Seshadri S, Shah A, and Bhade S. 1985. Haematologic response of
anaemic preschool children to acsrobic acid supplementation. Hum. Nutr.
Appl. Nutr. 39A: 151-154.
Teucher B, Olivares M, and Cori H. 2004. Enhancers of iron
absorption: ascorbic acid and other organic acids. Int J Vitam Nutr Res.
Ziegler EE. 2007. Adverse effects of cow's milk in infants.
Nestle Nutr Workshop Ser Pediatr Program. 60:185-96; discussion 196-9.