Boosting iron absorption: A guide to for the science-minded

Mothers and their young children are at elevated risk for iron deficiency. Can we solve the problem by eating lots of iron-rich foods? Yes, but success also depends on the bioavailability of dietary iron. Learn what influences iron absorption, and how you can improve your iron status by making smarter dietary choices.

foods rich in iron, like spinach, tofu, lentils, seeds, dried apricots, broccoli; also oranges for better absorption

Back in the Paleolithic, iron deficiency was probably uncommon (Eaton et al 1999). That’s because the Paleolithic diet included

  • animal muscle tissue (from mammals, birds, fish, and/or shellfish);
  • plant-based sources of iron (e.g., green leafy vegetables); and
  • foods rich in vitamin C (which can triple the bioavailability of iron).

Today, our diets deviate from the Paleolithic model, and iron deficiency is widespread, affecting approximately 20% of people around the world. Most live in low-to-medium income countries (Mantadakis et al 2020), but iron deficiency is quite common in affluent countries, too. Especially among certain high risk groups.

For example, it’s well known that women experience increased iron demands due to menstruation and pregnancy, so they are more likely to suffer from iron deficiency during their cycling years. In the United States, 9-16% of women in this life stage are iron deficient (Sekhar et al 2018). In some European countries, the rates may be even higher (Milman et al 2017).

What’s perhaps less well known is the heightened risk among young children. In a nationally representative sample, 15% of U.S. children between the ages of 12 and 23 months were iron-deficient (Gupta et al 2017). In studies conducted in affluent countries in Europe and Asia, rates have ranged anywhere from 4 to 30% for children between 6-36 months (van der Merwe and Eussen SR 2017; Chen et al 2020).

Why do so many young children experience iron deficiency? It’s normal for babies to be born with enough iron stores to keep them healthy for the first 6 months postpartum. But after this age, infants are at increased risk for iron deficiency if they don’t consume foods that are rich in iron.

Healthy iron levels are crucial for optimal grown and neurological development, so medical experts recommend that all babies — breastfed or formula-fed — begin consuming an iron-rich diet by the age of 6 months  (Berglund and Domellöf 2021; Miniello et al 2021; Van Elswyk et al 2021).

How to we protect mothers and young children against iron deficiency? Is it as simple as feeding our families foods with high iron content? Not exactly. We also need to consider what might be interfering with an individual’s ability to absorb iron. Here’s a overview of the bioavailability of iron, and what we can do to improve it.

Heme versus nonheme iron

The bioavailability of iron depends on several factors. People who are iron-deficient absorb iron more easily than people who are iron-replete. In addition, absorption depends on the specific form that dietary iron takes: heme iron or nonheme iron.

Heme iron

Heme iron is found in both animals and plants. But it’s most abundant in the blood and muscle tissues of animals. On average, humans absorb between 15-35% of the heme iron they consume (Insel et al 2003).

Nonheme iron

Nonheme iron is also found in both animals and plants, but nonheme levels are particularly high in certain plant foods. In fact, some plant foods actually pack more iron that meat does.

There’s a catch, though. The molecular form of nonheme iron makes it much less bioavailable to us, much harder for us to absorb. And iron-rich plant foods — like beans, seeds, grains, and leafy greens — often contain phytates, compounds that bind to iron, rendering it inaccessible to the body as it travels through the digestive tract (Kumar 2021).

Put these factors together, and you can see why most of the iron in plant foods doesn’t get incorporated into our bodies. We absorb only around 7% of the iron in soybeans. When we eat cooked spinach, we typically absorb no more than 2% of the iron (Scrimshaw 1991).

This sounds discouraging, especially if you’re a vegetarian or vegan.  But rest assured: It’s possible to improve your iron status by consuming plant-based, nonheme iron. The trick is to combine this form of dietary iron with ingredients that actively enhance absorption.

Boost bioavailability with iron absorption enhancers

Laboratory analyses and experiments confirm that you can increase nonheme iron absorption by adding one or more of the following to your meal:

  • vitamin C  (Teucher et al 2004; Fidler et al 2009; Dasa and Abera 2018);
  • lacto-fermented vegetables, like sauerkraut (Sheers et al 2015);
  • citric acid, which is found in citrus fruits, and has effects independent of vitamin C (Doumani et al 2020); and
  • malic acid, which is found in apples and pears (Shaw et al 2003).

How much does vitamin C increase iron absorption?

Research suggests it can have a powerful effect. In one study, 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). Higher concentrations of vitamin C have improved iron absorption up to 400% (Walczyk et al 2014).

And the other additives?

Lacto-fermented vegetables also have a sizable impact, improving the iron absorption of a high-phytate meal by 200% (Sheers et al 2016). And citric acid seems helpful too, though to a lesser degree. When 60 mg of citric acid were added to 240 grams of an oat-based nutritional beverage, iron absorption increased by more than 50%  (Zhang et al 2007).

Regarding malic acid, I haven’t found research that quantifies the benefit, but there’s a study of young children (ages 3 to 6) who were randomly assigned to consume an iron-rich meal with either orange juice or apple juice.

A cup of orange juice packs a whopping 124 mg of vitamin C, and it contains citric acid too. By contrast, a cup of apple juice has only 2.2 mg of vitamin C, along with some malic acid. So you might predict that kids would absorb more iron when they drank the orange juice, but that didn’t happen in this study. Instead, kids in both groups absorbed iron from their food to an equal degree (Shah et al 2003).

Finally, it’s worth noting that you can boost nonheme iron absorption by adding relatively modest amounts of meat to a meal. In experiments 50 to 85 grams of meat have increased iron absorption by 150 – 400% (Baech 2003; Baynes and Bothwell 1990; Cook et al 1976; Engle-Stone et al 2005; Navas-Carretero 2008).  

Be aware of iron absorption inhibitors

This is the flipside of the coin. Some compounds actively inhibit the absorption of iron, so we need to be aware them, too. There are the phytates, as already mentioned. There are also the polyphenols (which include tannins), as well as certain micronutrients and proteins.

It adds up to a broad range of foods and food ingredients that have the potential to inhibit iron absorption, including:

  • wheat germ, wheat bran, beans, peas, lentils, peanuts, and other plant foods containing phytates;
  • egg protein (from both the white and the yolk);
  • minerals that compete with iron for absorption, like calcium, zinc, magnesium, and copper;
  • tea, coffee, and cocoa; and
  • certain herbs, including peppermint and chamomile.

Even dietary fiber can reduce iron absorption, albeit to a modest degree (Cook et al 1983).

What should you do about these iron absorption inhibitors? As you can see, many of them are important — even crucial — for your health. So restriction isn’t a good idea.

But if you’ve been diagnosed with iron deficiency anemia, your doctor might recommend that you avoid consuming high levels of iron absorption inhibitors just before, during, or after a meal that is intended to boost your iron levels.  

And when it comes to phytates, remember: You can anticipate their iron-inhibiting effect and counteract it.

For example, chickpeas contain nonheme iron…and lots of phytates too. So the bioavailability of iron is low. People absorb only 3% of the iron in cooked chickpeas (Doumani et al 2020).

But if you turn the chickpeas into hummus — and add lemon juice (a source of both vitamin C and citric acid) — the iron becomes far more absorbable. More than 30% of the iron is now bioavailable (Doumani et al 2020).

Another approach is to time your daily vitamin C supplementation to coincide with an iron-rich meal. 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.

What effect does cow’s milk have on iron absorption?

As noted above, calcium is an iron absorption inhibitor (Hallberg 1998; Perales et al 2006). And studies report links between cow’s milk consumption and iron deficiency anemia in very young children. When babies  and toddlers consume unmodified cow’s milk (as opposed to breast milk, iron-fortified infant formula, or iron-fortified toddler’s milk), they are at higher risk for becoming iron deficient (Griebler et al 2016).

So it appears that cow’s milk could interfere with iron absorption. This has led a number of medical organizations, including the American Academy of Pediatrics, to recommend that you avoid giving babies unmodified cow’s milk until they are at least 12 months old (Riley et al 2018).

But for older kids? Studies indicate that many kids who drink milk have adequate iron levels. The key is to consume a well-rounded diet that includes lots of iron-rich foods and iron absorption enhancers.

Are there any other ways to improve your child’s iron status?

In the old days, people assumed that boosting iron meant persuading their children to liver or spinach — foods that many kids dislike. But there is a wide array of iron-rich foods, and many are child-friendly, so it can be helpful to review your options.

See this Parenting Science article, where I provide information about the iron content of many foods, including grains, fruits, and vegetables.

In addition, there are a variety of palatable, iron-fortified foods on the market, and they can be effective. Iron-fortified milk and cereal has helped reduce rates of iron deficiency among children around the world (Eichler et al 2012).

Finally, consider cooking with iron cookware. It can add iron to your diet,particularly if you cook acidic foods at high temperatures (Kuligowski and Halperin 1992; Sharma et al 2021).

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Content last modified 1/2022

image of iron rich foods and orange clices by istock / vaaseenaa