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Nutrition and Metabolism

Iron

What is iron?

Iron is an essential mineral for human body. It is what makes human blood red and is critical to blood function. Iron deficiency is the most common nutritional deficiency and the leading cause of anemia in the United States. It can cause fatigue that often results in poor work performance in adults.  Iron deficiency during pregnancy can lead to small or preterm babies. It can also delay normal motor or mental function in children.

How is iron used in human body?

About 74% of iron in men and 85% in women exists in heme, the functional component of hemoglobin, myoglobin and cytochromes. Hemoglobin transport oxygen in blood.  Myoglobin is the main component of muscles. Cytochromes are the electron transporters responsible for energy production. Noneheme iron functions as cofactor of many enzymes involved in energy conversion.

What is the normal iron level in human body?

Normal serum iron levels are in the ranges of 60 - 170 μg/dL for men and 30 - 126 μg/dL for women. Lower levels may indicate iron deficiency, chronic gastrointestinal blood loss or menstrual bleeding, or pregnancy. Higher levels may suggest iron overloading, broken blood cells, hepatitis, or vitamin B12 or B6 deficiency.  You need seek help from your health providers to interpret your blood iron test results.

How much iron do I need in my diet?

The RDA (Recommended Dietary Allowance) and UL (Tolerable Upper Intake Levels) for iron by the Institute of Medicine of the National Academies are age and gender dependent (Table 1). In general, children at rapid growth and women (especially pregnant women) need more iron.

Table 1. RDA and UL for dietary iron by the Institute of Medicine of the National Academies.

Age (group) RDA (mg/day) UL (mg/day)
1–3 years 7 40
4–8 years 10 40
9–13 years 8 40
14–18 years (men) 11 45
14–18 years (women) 15 45
14–18 years (lactating women) 10 45
14-18 (pregnant women) 27 45
19 and older (men) 8 45
19-50 years (women) 18 45
19-50 (pregnant women) 27 45
19-50 (lactating women) 9 45
51 and older (women) 8 45

Should I take iron supplement?

Iron supplementation is recommended when diet alone cannot restore deficient iron levels to normal within an acceptable timeframe. Supplements are especially important when an individual is experiencing clinical symptoms of iron deficiency anemia. However, always check with your health providers first before taking any supplements. Too much iron supplement can result in iron overload.

Why dietary iron is more important for people carrying certain gene variants?

Iron absorption and function are dependent on vitamin C. Two genes affecting the vitamin C levels in human body, the SLC23A2 gene and the Hp gene, also affects iron levels. For people who carry specific variants of these two genes, one variants in the SLC23A2 gene (28% worldwide) and another one in the Hp gene (48% to 52% worldwide), an increased risk for iron deficiency would more likely to develop if they did not meet the Recommended Dietary Allowance.

On the other hand, people carrying certain genetic mutations (such mutations in HFE or G6PD) can develop iron overload (hemochromatosis) when taking too much iron.  For people predisposed to iron overload, approximately one in 240 to 300 Caucasians, restricting heme iron rich foods such as iron supplements, animal livers, and red meats is encouraged.

Which foods contain high level of iron?

There are two forms of dietary iron: heme and noneheme. Heme iron is found in animal foods that originally contained hemoglobin. The highest levels are found in animal livers and red meats. Clam and oysters also contain considerable amount of iron. Noneheme iron is common in plants. Beans are good sources of noneheme iron. Noneheme iron is also the form of iron added to iron-fortified foods. Heme iron is absorbed better than noneheme iron.

Table 2 listed the most common iron rich foods. Many fortified foods in grocery stores, such as milk and ready-to-eat cereals, also have the amount of added noneheme iron listed in the Nutrition Facts on the label. They are not listed in Table 2.

Table 2. Common iron-rich foods.

Animal Livers
Goose liver pate
Per 100 g (mg) 17.9
Per Serving (mg) 15.2
Serving Size 3 oz (85 g)
Seeds
Seeds, Pumpkin and squash seed kernels
Per 100 g (mg) 8.8
Per Serving (mg) 2.5
Serving Size 1 oz (28 g)
 
Beans
Beans, Soybeans
Per 100 g (mg) 5.1
Per Serving (mg) 4.4
Serving Size 1/2 cup (86 g)
 
Beans, white
Per 100 g (mg) 3.7
Per Serving (mg) 3.3
Serving Size 1/2 cup (89 g)
 
Beans, Lentils
Per 100 g (mg) 3.3
Per Serving (mg) 3.3
Serving Size 1/2 cup (99 g)
Meats
Sea food, Oysters
Per 100 g (mg) 4.9
Per Serving (mg) 4.2
Serving Size 3 oz (85 g)
 
Sea food, Clams
Per 100 g (mg) 2.7
Per Serving (mg) 2.3
Serving Size 3 oz (85 g)
 
Duck, roasted
Per 100 g (mg) 2.7
Per Serving (mg) 6.0
Serving Size Half duck (221 g)
 
Beef, roast
Per 100 g (mg) 2.5
Per Serving (mg) 2.1
Serving Size 3 oz (85 g)
 
Lamb, shoulder
Per 100 g (mg) 2.4
Per Serving (mg) 2.0
Serving Size 3 oz (85 g)
Vegetables
Spinach
Per 100 g (mg) 3.6
Per Serving (mg) 6.4
Serving Size 1 cup (180 g)

How to get sufficient dietary iron intake?

First you are recommended to use the GB Food Calorie and Nutrition Calculator to get the most accurate estimate of your current iron intake.

To increase iron intake, the best way is to eat iron-rich foods as those shown in Table 2. Many fortified foods listed the iron content in the Nutrition Facts.  Choose the ones with high iron content during shopping.

Several dietary factors, including vitamin C, fructose, sorbitol, citric, and lactic increases iron absorption.  Since these factors are normally rich in fruits and vegetables, you should eat fruits and vegetables along with iron rich food to boost iron intake efficiency.

Meanwhile, several other dietary factors, mainly tea and coffee drinking, interfere with iron absorption.  Avoiding the consumption of these two drinks during iron will also help maintain an appropriate iron level.

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