Vegan Iron Sources – Cacao or Spinach?

Vegan iron sources: Why iron content is not the only thing that matters.

Iron is one of the nutrients that are considered potentially critical in a vegan diet. Therefore, vegans should be aware of vegan iron sources and how to get the most out of them in terms of bioavailability.

In principle, you can meet the intake recommendations of the professional nutrition societies for all nutrients (with the exception of vitamin B12) with a vegan diet. However, a less than optimal diet can lead to nutrient deficiencies. In addition, there are population groups with higher nutrient requirements, such as pregnant and lactating women, infants, children and adolescents, athletes, or in the case of some diseases and medication intake (Leitzmann and Keller, 2013; Piccoli et al., 2015; Melina et al., 2016; Keller and Müller, 2016). In this article, you will learn about the underlying mechanisms of iron utilization and how to achieve optimal iron status with vegan iron sources.

Both divalent and trivalent iron occur naturally, and although it is the fourth most abundant element on the Earth’s surface, iron deficiency is one of the most common nutrient deficiencies worldwide, according to the World Health Organization (WHO, 2004). It is therefore a global problem and by no means exclusive to vegans.

Functions of Iron

Iron transports oxygen in the blood, as it is the central component of hemoglobin. In muscles, iron serves as oxygen storage as part of myoglobin. Iron is also important for energy production (in cytochromes in the respiratory chain) and for the production of messenger substances in the body (hormones, neurotransmitters). As a pro-oxidant, iron fends off pathogenic (disease-causing) microorganisms.

The regulation of iron metabolism takes place with absorption. When the body needs more iron, it can mobilize it from iron stores (ferritin and hemosiderin in the liver, spleen, and bone marrow). If these stores are not sufficiently filled, more iron is absorbed from food (increased absorption rate).

Iron deficiency can impair physical performance and disrupt thermoregulation. Your immune system also depends on iron. Chronic low iron intake leads to iron deficiency anemia (a form of anemia), which is one of the most common deficiency symptoms worldwide (WHO, 2004).

Bioavailability

Iron is found in foods of animal and plant origin. However, depending on the form of iron present, It is absorbed to a greater or lesser extent by the body, which means, its bioavailability varies.

In the human organism, iron is present in its bivalent form (Fe2+) as heme iron. Due to its similarity to cells, it is also found in foods of animal origin in the form of hemoglobin and myoglobin. Once released from the food matrix, the heme molecule (prosthetic group of the chromoprotein) acts as a protective ring around the central iron ion, protecting it from interactions with other food components and preserving it in its soluble form in the intestine. As this, it is absorbed in the small intestine via a special transport system.

Plant sources, on the other hand, do not contain heme iron, but inorganic iron in the form of non-heme iron in its trivalent form (Fe3+). Since trivalent iron tends to form complexes and has a very low solubility at pH >5, it is less readily absorbed by the body than divalent iron. In addition, it can interact with other food components or be positively or negatively influenced in the absorption process. These are known as enhancing and inhibiting factors.

While the bioavailability (absorption rate) of trivalent non-heme iron is about 2–20 %, it is 15–35 % for divalent heme iron. The bioavailability of trivalent iron can be improved by vitamin C, fruit acids, organic acids, and sulfur-containing amino acids, which promote reduction to the more soluble divalent iron. Having vitamin C with it can increase the absorption of non-heme iron three- to four-fold. On the other hand, many components of plant foods, such as oxalates, phytates, tannins, and other polyphenols, inhibit the absorption of nonheme iron by forming complexes. Phosphate and some dietary fibers are also inhibitors (Leitzmann et al., 2009; Leitzmann and Keller, 2013). Phytic acid, or phytate, found in legumes, whole grains, seeds, and nuts, forms complexes with minerals such as iron, calcium, or zinc, inhibiting their absorption. Phytate content can be reduced by fermentation (e.g., letting whole-grain bread dough rise for a long time) or soaking and sprouting. These methods lead to the release of an enzyme (phytase) that breaks down phytic acid.

In addition, iron can be absorbed into the cells in the form of ferritin. This seems to be particularly the case in some types of lentils. Exactly how and to what extent this kind of uptake occurs is not yet fully understood (Theil et al., 2012).

Requirements and Status

The European Food Safety Authority (EFSA) recommends an intake of 11 mg/day for men and nonmenstruating women who are not pregnant or breastfeeding, and 16 mg iron/day for menstruating women. In contrast to other nutrition societies, EFSA does not give higher recommendations for pregnant women. The German Nutrition Society doubles its intake recommendation from 10 to 20 mg iron per day during that time (EFSA, 2015).

These intake recommendations only partially take into account bioavailability for the vegan diet: the actual average iron requirement is 6 mg/d. The intake recommendations are based on an average absorption rate of 16 % for men and 18 % for women (EFSA, 2015). However, taking into account the assumed absorption rate of 2 % mentioned above, the daily intake may not be enough to meet the requirements even though the absolute recommended amount of iron has been provided. In the USA, vegetarians are recommended to consume 1.8 times more iron than non-vegetarians for this reason (Institute of Medicine, 2001).

You can determine your individual status with blood tests. Serum iron is a blood marker which shows short-term iron status, but it is of limited significance. The level of serum ferritin (iron storage), as a long-term parameter, can give you a more reliable indication of your iron status. The hemoglobin content, the erythrocyte count and the hematocrit value (blood viscosity) are also determined as part of the CBC.

Significant amounts of iron are lost during blood loss (menstruation, phlebotomy, surgery, etc.) (approximately 1 mg of iron per 2 ml of blood). During the menstrual cycle, an average blood loss of 30–60 ml can be expected, i.e. 15–30 mg of iron gets lost from the body (Lönnerdal et al., 2006; Hoppler et al., 2009; Schweitzer, 2014).

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Deficiency

Iron deficiency is one of the most common nutrient deficiencies worldwide. Manifest deficiency leads to anemia, which particularly affects pregnant women, infants and children, especially in developing countries.

The population in industrialized countries is more affected by so-called latent iron deficiency. This results in a lack of oxygen in the cells, causing symptoms such as fatigue, headaches and paleness.

In the case of an acute deficiency, temporary supplementation after medical consultation can replenish the stores and subsequently maintain the levels. Unless diagnosed, high-dose dietary supplements are not recommended because of the risk of oversupply, which can increase the risk of coronary heart disease.

Occurence

A variety of plant foods can be considered good vegan iron sources, especially legumes, whole grains, vegetables, nuts, seeds, and dried fruits.

• legumes: lentils, beans (mung beans, soybeans, white beans and products made from them, such as tofu), chickpeas, etc.
• nuts and oilseeds: pumpkin seeds, sesame seeds (or tahini), flax seeds, pistachios, sunflower seeds, etc.
• grains and pseudo-grains: amaranth, quinoa, millet (grain), oats (grain), spelt and green spelt (grain), brown rice, etc.
• vegetables: fennel leaf, purslane, endive, corn salad, cooked black salsify, rocket, zucchini, etc.
• dried fruit: peach, apricot, banana, date

Table 1: Iron Content of Plant Foods (Elmadfa et al., 2017; BLS; USDA; Heseker and Heseker, 2019)

Status of Vegans

Several studies have shown that adult vegetarians tend to have similar or higher iron intakes than non-vegetarians (Deriemaeker, 2010). Because dairy products are not a significant source of iron, vegans sometimes get more iron than vegetarians and people following an omnivorous diet (Davey, 2003). However, the lower bioavailability of non-heme iron makes this higher intake necessary to meet requirements or can still lead to an inadequate status.

Iron status must be considered in a nuanced manner: While the concentrations of serum iron and hemoglobin of vegans are about the same as those of people on a mixed diet, the long-term parameter, iron ferritin, is often below theirs. However, it is usually still in the lower normal range (Ball and Barlett, 1999; Wilson and Ball, 1999; Śliwińska et al., 2018).

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Summary

Iron is a potentially critical nutrient not only for vegans, but especially for menstruating women, regardless of diet. Since vegan iron sources only contain non-heme iron, you should look for clever combinations and processing methods in your food choices to increase the low bioavailability. Examples are homemade hummus with bell pepper sticks, freshly squeezed orange juice with oatmeal, fermented soy products such as miso or tempeh, and dried fruit with nuts. Soaking and sprouting legumes, whole grains, and nuts also increases the bioavailability of iron. You can reduce inhibitors by avoiding coffee and green and black tea during and after an iron-rich meal.

The content of this article cannot and should not replace individualized vegan nutrition counseling. You can find expert help in your area or online in the International Directory for Vegan Nutritionists.