Nutrient Information: Iron, Fe

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Nutrient Key Information 
Nutrient Name: Iron, Fe
Nutrient Category: Minerals
Measuring Unit: mg
Nutrient Summary: Iron is a critical component of hemoglobin, which transports oxygen from the lungs to tissues throughout the body. A person should get adequate iron intake to increase the red blood cell formation capability.
Nutrient Function: Iron is a critical component of several proteins: hemoglobin, myoglobin, and cytochromes. Its key role is to transport oxygen in blood and muscle.
• Make hemoglobin in red blood cell which transports oxygen from the lungs to tissues throughout the body for metabolism.
• Make myoglobin, a protein to provide oxygen to muscles.
• Required for red blood cell production in the bone marrow.

It also plays other roles in the body:
• Essential for activating certain enzymes and for making amino acids, collagen, neurotransmitters, and hormones
• Needed for the metabolism of energy nutrients to produce energy
• Help growth and development
• Play the role in immune function for immune cells proliferation and maturation
• Help with wound healing

• ~2/3 body iron is in hemoglobin which is involved in the transport of oxygen from lungs to tissues throughout the body for metabolism.
• ~25% body iron is in mobilizable iron store stored as ferritin in liver, spleen, and bone marrow.
• ~15% body iron is in the myoglobin of muscle tissue.

Iron, Fe Interactions With Other Nutrients 
Vitamin C, total ascorbic acid
Vitamin C enhances nonheme iron absorption

Vitamin C helps convert ferric iron (Fe3+) found in plant-based foods into ferrous iron (Fe2+). Ferrous iron is more soluble and easier for the body to absorb in the small intestine. So including vitamin C-rich foods or beverages in the meals containing iron-rich plant foods can significantly improve iron absorption.

Manganese, Mn
Iron intake and iron store status in the body have an inverse relationship with manganese absorption

Both iron and manganese use and compete Divalent Metal Transporter 1 (DMT1) for uptake them into intestinal cells. Iron supplements can inhibit manganese absorption more significantly than dietary iron because supplements provide a concentrated source of iron.

The body's iron stores influence the expression of DMT1. When iron stores are low (iron deficiency), the body upregulates DMT1 to increase iron, as well as manganese, absorption. Conversely, when iron stores are high, DMT1 expression is downregulated, which can reduce the absorption of both iron and manganese.

Zinc, Zn
Iron and zinc supplements may decrease each other's absorption

Iron and zinc share a common absorption pathway in the intestines, high concentration of one mineral can potentially inhibit the absorption of the other due to competition for this transporter. In addition, iron supplements can form insoluble complexes with zinc in the gastrointestinal tract, that reduce the availability of zinc for absorption.

When taking high bioavailability Ferrous Sulfate iron supplement, especially without food, the impact to the zinc absorption is more pronounced. The higher the iron supplement dosage, the severe the zinc absorption reduction. It is true vice versa.

Recommend to separate the intake of iron and zinc supplements by a few hours to reduce direct competition for absorption. It is better to obtain heme iron from animal products which is less likely to interfere with zinc absorption, and also make sure to get sufficient zinc from food sources such as meat, shellfish, seeds, nuts, cheese, and whole grains.

References: Iron and Zinc Homeostasis and Interactions: Does Enteric Zinc Excretion Cross-Talk with Intestinal Iron Absorption?
Calcium, Ca
Calcium can inhibit the absorption of iron

Several studies have shown that calcium, whether from food or supplements, can reduce the absorption of non-heme iron (found in plant-based foods) when they are consumed simultaneously. The calcium-iron complexes that form in the intestine reduce the amount of iron that can be absorbed. However, this inhibitory effect is temporary.

To optimize iron absorption, it is better to consume calcium-rich foods or supplements at different times than iron-rich meals, especially meals containing iron-rich vegetables.

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Food Sources

Heme iron (with higher absorption rate ~25%):
• Organ meat (such as liver)
• Lean meat
• Seafood (such as tuna, sardines, haddock, shrimp, oysters, clam)
• Poultry
• Eggs

Nonheme iron (with lower absorption rate ~16.8%):
• Beans (such as kidney beans, pinto beans), lentils, and peas
• Soy products (such as tofu)
• Nuts (such as cashews and almonds) and seeds (such as pumpkin seeds)
• Green vegetables (such as spinach, kale, broccoli, and collard greens)
• Iron-fortified breakfast cereals and breads, and whole grain
• Dried fruits (such as raisins and prunes)
• Eggs
• Meat, seafood, and poultry

For vegan diet (pure vegetarian), the key food sources of Iron are as following:
• Fortified cereals, enriched and whole grains
• Legumes, such as black-eyed peas, kidney beans, pinto beans, lentils
• Dark green leafy vegetables, such as spinach, turnip greens
• Dried fruits, such as apricots, prunes, raisins
Vegetarians need higher amount of iron food intake because of the lower iron bioavailability from vegetables.

The factors which can enhance nonheme iron absorption:
• Vitamin C ascorbic acid
• Meat, fish, and poultry
• Acids (citric and lactic)
• Sugars (fructose)

The factors which inhibit nonheme iron absorption:
• Phytate: in foods such as soybeans, black beans, lentils, mung beans, split peas, and unrefined rice and grains.
• Polyphenols: in foods such as tea, coffee, many grain products, and red wine.
• Calcium inhibits the absorption of iron, especially nonheme iron from plant-based foods.
• Dairy products (such as cow milk) reduce iron availability. Spacing the intake of iron-rich foods or iron supplements with dairy products for about 1 hour.

Learn more about heme iron vs nonheme iron in the article:
Heme, an Essential Nutrient from Dietary Proteins, Critically Impacts Diverse Physiological and Pathological Processes

Sample Foods High in: Iron, Fe
View Additional Food Sources
Food Description Nutrient Amount1 Daily Value%2
Pork, fresh, variety meats and by-products, liver, cooked, braised
Category: Pork Products
17.92 mg 99.56%
Chocolate, dark, 70-85% cacao solids
Category: Sweets
11.9 mg 66.11%
Mollusks, oyster, eastern, wild, cooked, moist heat
Category: Finfish and Shellfish Products
9.21 mg 51.17%
Seeds, pumpkin and squash seed kernels, roasted, without salt
Category: Nut and Seed Products
8.07 mg 44.83%
Beef, plate steak, boneless, outside skirt, separable lean and fat, trimmed to 0" fat, all grades, cooked, grilled
Category: Beef Products
5.09 mg 28.28%
Spinach, cooked, boiled, drained, without salt
Category: Vegetables and Vegetable Products
3.57 mg 19.83%
Beans, kidney, all types, mature seeds, cooked, boiled, without salt
Category: Legumes and Legume Products
2.22 mg 12.33%
1 Nutrient amount is in 100 gram food
2 Use FDA 2000 calorie diet as Daily Value reference

Additional Nutrient Information
Nutrient Summary Iron is a critical component of hemoglobin, which transports oxygen from the lungs to tissues throughout the body. A person should get adequate iron intake to increase the red blood cell formation capability.
Deficiency Health Effects Worldwide, iron deficiency is one of the most common nutrient deficiencies. Primarily impacts children and women of childbearing age. Here are some iron deficiency effect and symptoms:
• Iron deficiency anemia, with low hemoglobin concentration caused by the severe depletion of iron stores
• Reduced physical work capacity
• Impaired cognitive function
• Reduced capacity of immune response
• Delayed psychomotor development in infants

Iron deficiency detection stages:
• Stage 1: measure serum protein ferritin in the blood which reflects iron stores status. The less the worse.
• Stage 2: measure serum protein transferrin in the blood which transports iron. The more transferrin and the less serum ferritin the worse.
• Stage 3: the lack of iron starts to limit the red blood cell hemoglobin production. This is detected by measuring hemoglobin and hematocrit amount. The less the worse.

1) Iron-deficiency anemia can impair aerobic activities performance, like long distance running, because aerobic activities require hemoglobin in red blood cells to deliver oxygen to the body cells for energy metabolism. To prevent from iron deficiency, physically active people, especially athletes, need to intake high quality iron rich foods and vitamin C-rich foods with each meal.
Effects if Above Upper Limit Excessive iron could be caused by:
• Massive doses of iron supplements
• Hemochromatosis disorder which causes bodies to absorb too much iron (more than what our bodies need) from the foods
• Excessive alcohol which could damage the small intestine and increase the risk of hemochromatosis
• Repeated blood transfusions which bypass the intestinal defense on iron absorption

The excessive irons are accumulated in the liver, heart, joints, and other tissues. Iron overload could cause the following symptoms and health problems:
• Excessive free irons act as free radical, they can attack cell lipids, DNA, and protein. Body tries to create storage protein called hemosiderin to avoid free irons. Hemosiderin is the iron protein in addition to the regular iron storage protein ferritin.
• Gastrointestinal distress, such as constipation and nausea
• Acute toxicity with vomiting and diarrhea
• High doses of iron may decrease zinc absorption
• Untreated iron overload can lead to cirrhosis, liver cancer, heart failure, and arthritis.
External References
Additional Information Iron is a trace mineral (also called micromineral) which means human body requires in relatively small amounts (less than 100 milligrams per day).

Daily Value Age Group Recommended Daily Values Daily Value Upper Limits
Toddler 1 to 3 years old: 7 mg 40 mg
Child 4 to 8 years old: 10 mg 40 mg
Male 9 to 13 years old: 8 mg 40 mg
Male 14 to 18 years old: 11 mg 45 mg
Male 19 to 30 years old: 8 mg 45 mg
Male 31 to 50 years old: 8 mg 45 mg
Male 51 to 70 years old: 8 mg 45 mg
Male Senior 71 or older: 8 mg 45 mg
Female 9 to 13 years old: 8 mg 40 mg
Female 14 to 18 years old: 15 mg 45 mg
Female 19 to 30 years old: 18 mg 45 mg
Female 31 to 50 years old: 18 mg 45 mg
Female 51 to 70 years old: 8 mg 45 mg
Female Senior 71 or older: 8 mg 45 mg
Female Pregnancy (>18): 27 mg 45 mg
Female Lactation (>18): 9 mg 45 mg
FDA (Based on 2000 calorie daily diet): 18 mg

Dietary Reference Intakes The nutrient Dietary Reference Intakes and nutrition facts is from Institute of Medicine of National Academies 2006. Dietary Reference Intakes: The Essential Guide to Nutrient Requirements. Washington, DC: The National Academies Press.
US FDA Nutrition Education Nutrition facts knowledge are based on U.S. FOOD & DRUG Administration Nutrition Education Resources & Materials.
National Institutes of Health Nutrition facts knowledge are based on National Institutes of Health Dietary Supplement Fact Sheets.
Disclaimer The nutrient information provided here should not take the place of medical advice. We encourage you to talk to your healthcare providers (such as your doctor) about your dietary requirements which are best for your overall health. We also recommend you to read organization or professional reference documents or articles mentioned, but not limited to, in this page. Any mentions and reference links in this page don't represent our endorsement of their services and advice.

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