Micronutrients: Iron

Micronutrients: Iron

Iron is a mineral that plays many roles in human health, including supporting metabolism, growth and immunity. Iron also is an essential component of hemoglobin and myoglobin, which are responsible for transporting oxygen to the body’s tissues and muscles.

Approximately half of all cases of anemia are due to iron deficiency, which can be fatal. The World Health Organization considers iron-deficiency anemia to be the world’s most common nutritional deficiency, affecting more than 50 percent of preschool aged children and pregnant women in developing nations and 30 percent to 40 percent in industrialized nations. Iron fortification of wheat flour, now mandated in 83 countries, has proven to be a practical approach to increasing iron intake.

Food sources mg/serving rating
1 serving fortified breakfast cereal 18mg Excellent
1 cup canned white beans 8mg Excellent
3 ounces pan-fried beef liver 5mg Excellent
? cup boiled and drained spinach 3mg Good
? cup firm tofu 3mg Good
3 ounces braised bottom round beef, trimmed 2mg Good
1 ounce oil-roasted cashews (18 nuts) 2mg Good

Sources of iron
Dietary iron is found in two forms: heme from meat and other animal sources and non-heme from plant and iron-fortified foods.

Heme iron is less affected by other dietary factors and is highly bioavailable (15 percent to 35 percent absorption) compared to non-heme iron, which is less bioavailable (1 percent to 23 percent absorption) and affected by other foods. In general, people who eat a variety of foods, including meat and seafood, absorb 14 percent to 18 percent of the iron they consume, while those who eat a vegetarian diet absorb 5 percent to 12 percent, however, this can vary with diet and iron status.

Many people consume more non-heme iron than heme iron. Eating a source of vitamin C or poultry, meat or fish with non-heme iron foods can enhance the bioavailability of iron. Some foods and beverages such as soy and tea may affect iron absorption, but these effects are generally modest for people who eat a varied diet.

The Daily Value, or DV, for iron is 18 milligrams for people age 4 and older. Foods with 20 percent or more of the DV are considered excellent sources, and those with 5 percent or less are considered low in iron.

Iron dietary supplements often are recommended for people at risk for deficiency, such as infants, young children, teenage girls, pregnant women and premenopausal women.

Full-term healthy infants generally receive enough iron from their mothers to last four to six months. At 4 months old, supplemental iron is recommended for infants who are breastfed until iron-containing complementary foods are introduced.

Iron supplements can reduce the absorption of certain medications, such as levodopa and levothyroxine. Proton pump inhibitors can reduce iron absorption. Always discuss iron supplementation with a health care provider.

Current recommendations
The Health and Medicine Division of the National Academies of Sciences, Engineering and Medicine (formerly the Institute of Medicine) sets Recommended Dietary Allowances, or RDAs, for iron (mg/day). (See chart below.)

Age Male Female Pregnancy Lactation
Birth to 6 months 0.27 mg* 0.27 mg*
7–12 months 11 mg 11 mg
1–3 years 7 mg 7 mg
4–8 years 10 mg 10 mg
9–13 years 8 mg 8 mg
14–18 years 11 mg 15 mg 27 mg 10 mg
19–50 years 8 mg 18 mg 27 mg 9 mg
51+ years 8 mg 8 mg
*Based on Adequate Intake of iron in healthy breast-fed infants

The Tolerable Upper Intake Level is 40 milligrams per day from birth to 13 years and 45 milligrams per day for people 14 and older, including those who are pregnant or breast-feeding.

Iron deficiency occurs with inadequate consumption or absorption and excessive iron losses.

The most common measurement of iron status is hemoglobin via blood draw, but definitive diagnosis requires additional biomarkers. Hemoglobin concentrations below 13 grams per deciliter for men and 12 grams per deciliter for women indicate iron-deficiency anemia.

Infants, young children, adolescent girls, female athletes, pregnant and premenopausal women, and women with heavy menstrual periods have the greatest risk for iron deficiency.

Children and pregnant women are the most vulnerable, given their increased nutrient needs. During pregnancy, iron-deficiency anemia increases the risk of low birth weight infants and maternal and perinatal mortality.

Pregnant women should be tested for anemia at the first prenatal visit and again during the third trimester. Infants also should be screened; exact timing varies and should be determined by a pediatrician. Emerging evidence suggests iron deficiency during infancy and childhood may have long-lasting detrimental effects on cognitive and neurodevelopment.

Also at risk are people with cancer, chronic blood loss, gastrointestinal disorders, chronic disease such as chronic infections and auto-immune disease, heart failure and nutrient deficiencies as well as frequent blood donors.

Symptoms of iron-deficiency anemia may include fatigue, pale skin and fingernails, weakness, dizziness, headache or swollen tongue.

Healthy adults are at very low risk of overconsuming iron, except from dietary supplements. As little as 20 milligrams and more likely at 60 milligrams of iron per kilogram of body weight can cause symptoms of acute toxicity, including abdominal pain, nausea, vomiting and constipation, or even organ failure and possibly death.

People with the genetic disorder hemochromatosis are at increased risk of iron toxicity and require treatment to prevent iron overload.

Bottom line
Iron is an essential micronutrient that is tied to many bodily functions. Ideally, most people will meet their iron needs through diet; in high-risk populations, supplementation may be advised.


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Kathleen Zelman
Kathleen Zelman, MPH, RDN, is the nutrition director of WebMD.