Key Concepts

  • Iron deficiency is the most common nutritional deficiency in the world
  • RDA – Men (8mg/day); Women (18mg/day, 8mg/day post-menopause)
  • UL – 45 mg/day
  • Heme iron (from animals) is absorbed better than non-heme iron (from plants) – non-heme iron absorption is enhanced with vit C
  • Food Sources: Heme (Meat, poultry, fish); non-heme (nuts, seeds, legumes, green leafy vegetables)
  • Using a cast-iron skillet to cook foods can significantly increase non-heme dietary iron

Recommended Dietary Allowance (RDA)

  • Men – 8mg/day
  • Women 18 mg/day (19-50 yrs old); 8mg/day (51+)
  • Pregnancy 27 mg/day

The need for dietary iron is dependent on several factors including age, sex, pregnancy, and lactation. Click here for a full table. In general, as blood volume increases during pregnancy, the need for iron also increases. Some iron is transferred across the placenta to the developing fetus. In menopause there is not the loss of blood occurring each month so the need for iron decreases.


Iron comes in two forms, ferrous iron (reduced) Fe2+ and ferric iron (oxidized) Fe3+. Iron can be associated into a coordination complex consisting of a porphyrin ring in which iron is the central atom. There is also non-heme iron which is not incorporated into a porphyrin ring. Heme proteins are oxygen carriers incorporated into hemoglobin and myoglobin. Heme proteins are also found in electron transport cytochromes and are activators of molecular oxygen. Non-heme proteins are co-facors in enzymatic reactions and are essential in DNA synthesis and repair.


About forty percent of the iron found in meat and fish is bound into heme; the other city percent is non-heme iron. All plant foods such as nuts, seeds, and vegetables contain non-heme iron. Heme iron is absorbed at about 25% while non-heme iron is absorbed at a maximum of about 17%. Therefore animal sources of dietary iron are better absorbed than non-animal sources, although it is still possible to obtain all dietary iron requirements from plant-based food sources.

Non-heme iron absorption is enhanced by vitamin C, acids, and fructose. Eating meat products will also enhance the absorption of non-heme iron. Phytates, vegetable proteins, calcium, milk proteins, and tannic acid inhibit the absorption of non-heme iron. So, legumes, grains, rice, soybeans, nuts, tea, and coffee can inhibit non-heme iron absorption.


Iron deficiency is the most common nutritional deficiency in the world.

Iron deficiency can lead to storage iron depletion and eventually to iron deficiency anemia. Symptoms of iron deficiency anemia (microcytic hypochromic anemia) include fatigue, weakness, tachycardia (elevated resting heart rate), and tachypnea (abnormally rapid breathing). Restless leg syndrome and impaired cognitive development in children due to hypomyelination of neurons and disrupted dopamine metabolism can also occur.

Those at risk for iron deficiency are children between 6 months old to 4 years old, pregnant women, those who have had significant blood loss, individuals with Celiac disease, inflammatory bowel disease, atrophic gastritis, vegetarians, vegans, and those who exercise intensely on a regular basis.

Toxicity/Excess/Upper Limit (UL)

Iron is stored as ferritin on a short-term basis in the intestinal mucosal cells and long-term in the liver and muscles. Copper is required for proper transport of iron (as transferrin) across the cell.

The upper intake level (UL) for iron is set at 45 mg/day for adults. Individuals with hemochromatosis, a genetic condition leading to iron overload, may experience toxicity symptoms at lower doses. These individuals are susceptible to cirrhosis of the liver, diabetes, and cardiomyopathy. Avoiding iron-rich foods and regular phlebotomy are practices used to treat hemochromatosis.

Food Sources


  • Oysters, eastern, cooked with moist heat, 3 ounces – 8mg
  • Beef, 3 oz – 1.6 mg
  • Chicken, liver, cooked, pan-fried, 1 oz – 3.6 mg


  • Potato, with skin, baked – 1 medium – 1.8 mg
  • Quinoa, cooked, 1/2 cup – 1.4 mg
  • Spinach, cooked, 1 cup – 6.4 mg
  • Lentils, cooked, 1/2 cup – 3.3 mg
  • Tofu, regular, raw, 1/2 cup – 6.6 mg

Cast-Iron Pan

Using a cast-iron pan can significantly increase the amount of iron present in foods.

  • Beef Stew – .66 mg —> 3.4 mg
  • Chili – 0.86 mg —> 6.27 mg
  • Pancake – 0.63 mg –> 1.31 mg
  • Rice – 0.67 mg –> 1.97 mg
  • Egg (Scrambled) – 1.49 mg–>4.76 mg
  • Spaghetti Sauce – 0.61 mg –> 5.77 mg

Acidic foods, like canned tomatoes, are particularly effective at leaching iron out of the pan and into the food you are eating. The form of iron in a cast-iron pan is non-heme iron.


Ferrous gluconate may be better absorbed than prescription iron supplements.

Because calcium inhibits the absorption of both heme and non-heme iron, it is best to not take calcium and iron supplements together. Dairy can also inhibit the absorption of iron.

Vitamin C enhances the absorption of iron so taking these supplements together makes sense.

Iron supplements may inhibit zinc absorption, although iron obtained from food has not been shown to inhibit zinc absorption.

Copper deficiency may exacerbate iron deficiency anemia.




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