- Iron and a Plant-Based Diet
- Dietary Reference Intakes for Iron
- Iron Content of Plant Foods
- Vitamin C Content of Plant Foods
- Functions of Iron
- Symptoms of Iron Deficiency
- Stages of Iron Deficiency
- Conditions that Exacerbate Iron Deficiency
- How Much Iron is Too Much?
Iron and a Plant-Based Diet
If you’re healthy and eat a varied vegan diet, you don’t need to worry about iron as it’s plentiful in a vegan diet. However, some people have trouble absorbing enough plant iron and if you think your iron stores might be low, you can increase iron absorption by:
- Adding a source of vitamin C at meals—see the table below, Vitamin C in Foods.
- Avoiding tea and coffee at meals.
- Increasing legume (peanuts, beans, lentils, peas) intake.
- Cooking foods (especially water-based acidic foods like tomato sauce) in cast iron skillets.
- Avoiding calcium supplements with meals.
If your concerns persist, have a doctor measure your iron status. If your iron stores are low, your doctor might suggest eating meat or taking an iron supplement. Anemia in meat-eaters is normally treated with supplemental iron, not with eating more meat. Similarly, vegans with anemia don’t need to start eating meat but can also be treated with supplemental iron and vitamin C.
It’s important for any vegan with iron deficiency to correct it because, during iron deficiency, the body has a tendency to absorb too much manganese. Luckily, vitamin C increases iron absorption but does not increase manganese absorption.
Dietary Reference Intakes for Iron
The table below lists the Dietary Reference Intakes for iron.
|Dietary Reference Intakes (DRI) for Iron|
|Female > 50||8||45|
|Breastfeeding ≤ 18||10||45|
|Breastfeeding > 18||9||45|
In the United States, iron amounts listed on a nutrition label are a percentage of the Daily Value for iron which is 18 mg/day. For example, 25% of the Daily Value = .25 x 18 mg = 4.5 mg.
Iron Content of Plant Foods
The table below shows a range of plant foods including those richest in iron.
|Iron Content of Plant Foods|
|Grape Nuts cereal||1/2 C||16|
|Total cereal—whole grain||1/2 C||8.0|
|Spinach||chopped, boiled||1/2 C||3.2|
|Kidney beans||boiled||1/2 C||2.6|
|Garbanzo beans||boiled||1/2 C||2.4|
|Swiss chard||chopped, boiled||1/2 C||2.0|
|Pinto beans||boiled||1/2 C||1.8|
|Dried figs||dried, raw||1/2 C||1.5|
|Soymilk||1 C||1.0 – 1.5|
|Rice—white, enriched||cooked||1/2 C||1.4|
|Peas – green||boiled||1/2 C||1.2|
|Pistachios||dry roasted||1/4 C||1.2|
|Sunflower seeds||dry roasted||1/4 C||1.2|
|Collard greens||chopped, boiled||1/2 C||1.1|
|Sweet potato||baked, w/skin||1/2 C||0.7|
|Rice—white, unenriched||cooked||1/2 C||0.7|
|Bread—whole wheat||1 slice||0.7|
|Peanut butter||2 T||0.6|
|Kale||chopped, boiled||1/2 C||0.6|
|Broccoli||chopped, boiled||1/2 C||0.5|
|Taken from the USDA National Nutrient Database or food labels.|
Vitamin C Content of Plant Foods
Eating a food high in vitamin C with meals can increase the absorption of plant iron. The table below shows the common plant foods highest in vitamin C.
|Vitamin C in Foods|
|Broccoli||chopped, cooked||1/2 cup||50|
|Strawberries||whole berries||1 cup||85|
|Yellow peppers||chopped||1/4 cup||70|
|Red peppers||chopped||1/4 cup||50|
|Also found in other green leafy vegetables (kale, collards, Swiss chard, Brussels sprouts), green bell peppers, and cauliflower.|
Functions of Iron
The major functions of iron are:
- Energy production
- Oxygen transport via the hemoglobin of red blood cells.
- Oxygen transport to the muscles via myoglobin.
- Part of the enzyme NADH dehydrogenase in the electron transport chain that produces ATP.
- Immunity—Iron has pro-oxidation properties used by the immune system to destroy bacteria.
- DNA synthesis
Symptoms of Iron Deficiency
Many iron deficiency symptoms are related to tissue oxygen deprivation: fatigue, rapid heart rate, palpitations, rapid breathing on exertion, and increased lactic acid production.
Iron deficiency anemia symptoms include pale skin, brittle fingernails, koilonychia (spoon-shaped fingernails where the outer edges are raised), weakness, loss of appetite, hair loss, impaired immunity, angular stomatitis (irritation and fissuring in the corners of the lips), glossitis (inflammation of the tongue), chronic gastritis, pica, abnormal temperature regulation, and delayed psychomotor development in children.
Stages of Iron Deficiency
Iron deficiency is the most common nutrient deficiency in the U.S. There are three stages as follows.
Stage 1. Storage Iron Depletion
Storage iron depletion is typically measured by serum ferritin (the protein on which iron is stored) of less than 18 ng/ml. When serum ferritin drops below 12 ng/ml, iron stores are completely depleted.
Note that ferritin levels can be raised, even in the presence of iron deficiency, in states of inflammation, infection, liver disease, weight gain, significant alcohol consumption, and elevated plasma glucose.
Another indication of storage iron depletion is an elevated total iron binding capacity—a measure of available spots for iron on the transferrin molecules that transport iron.
Stage 2. Early Functional Deficiency
In early functional iron deficiency, red blood cell formation starts to become impaired, but not enough to cause a measurable anemia. This is indicated by low serum transferrin saturation, increased erythrocyte protoporphyrin, and/or increased soluble serum transferrin receptor concentration.
Research has shown that iron supplementation for people in Stage 2 can reduce fatigue and increase cognition—see Iron Part 2—Research for more info.
Stage 3. Iron Deficiency Anemia
The Centers for Disease Control defines iron deficiency anemia as iron deficiency and a low hemoglobin value, typically less than 120 g/l. It’s characterized by small red blood cells due to a lack of hemoglobin.
Low values for hemoglobin concentration in blood, red blood cell count, hematocrit (the percentage, by volume, of red blood cells in whole blood), low mean corpuscular volume (the size of the average red blood cell), and erythrocyte hemoglobin concentration are all potentially indicative of iron deficiency anemia.
Because iron deficiency is not the only cause of anemia, multiple measures of iron status should be taken to determine if an anemia is truly from iron deficiency, as there are dozens of types of anemia (including anemia caused by low vitamin B12 levels).
Iron deficiency, with or without anemia, can impair muscle function and limit work capacity. Performance has been shown to improve with iron supplementation in athletes who are iron-deficient but not anemic (1, 2).
The average requirement for iron may be 30%–70% higher for those who engage in regular, intense endurance exercise, especially running. This is due to red blood cell destruction during and gastrointestinal blood loss after running (3). But, this doesn’t necessarily mean that the RDA for runners should be 30–70% higher as the RDA provides a buffer above the average iron requirement.
According to the American College of Sports Medicine, “Athletes who are vegetarian or regular blood donors should aim for an iron intake greater than their respective RDA,” and “Athletes, especially women, long-distance runners, adolescents, and vegetarians should be screened periodically to assess and monitor iron status.” They add that this is especially true during adolescence and pregnancy (1).
Conditions that Exacerbate Iron Deficiency
Any disease or medication that causes bleeding, including internal bleeding, or any disease of the digestive tract, could potentially aggravate or cause iron deficiency.
If you have a case of stubborn iron deficiency, have your doctor consider such conditions and medications before assuming it’s simply due to a low iron intake or poor absorption of plant iron.
Celiac disease is a condition in which gluten (from wheat, barley, and rye) causes an autoimmune reaction against the intestinal cells, and can cause some cases of otherwise unexplained iron deficiency anemia (4).
Celiac often causes severe diarrhea, vomiting, and other problems, but other times celiac disease goes undetected. It occurs in about 1 in 133 people in the USA (4).
Proton Pump Inhibitors
Proton pump inhibitors are widely prescribed to treat gastrointestinal diseases. Research has shown that they can cause iron deficiency anemia (5).
How Much Iron is Too Much?
Some research has associated high iron levels with chronic disease. As of 2001, the last time iron recommendations were updated by the Food and Nutrition Board (FNB), there wasn’t enough information to base an Upper Limit on concerns about chronic disease, so the current Upper Limit of 45 mg/day of iron for adults is based on the level that causes digestive pain.
Iron deficiency anemia is normally treated with 100–200 mg/day of iron for 4–6 months, and the Upper Limit isn’t intended to apply to iron therapy under medical supervision. Such large amounts of iron can cause nausea, diarrhea, or constipation, and should only be taken under a doctor’s care. Taking iron supplements with food can often alleviate such problems.
Iron overdose is a common cause of poisoning death in children. Symptoms of acute toxicity occur at iron intakes of 20–60 mg/kg of body weight and death occurs at approximately 200–250 mg/kg.
Iron overdose is an emergency situation because the severity of the toxicity is related to the amount of iron absorbed, which will increase over time. Symptoms can subside but then return 12–48 hours after ingestion.
1. American Dietetic Association; Dietitians of Canada; American College of Sports Medicine, Rodriguez NR, Di Marco NM, Langley S. American College of Sports Medicine position stand. Nutrition and athletic performance. Med Sci Sports Exerc. 2009 Mar;41(3):709-31.
3. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press, 2001.