Iron: Health Benefits and Risks of Overload
Dietary iron is probably best known for its role as an oxygen transporter within the body. As part of the blood protein hemoglobin it picks up oxygen in the lungs and carries it to the cells throughout the body. For this reason and also because of its role in activating T-cells and enhancing the ability of white blood cells to fight bacteria, iron is an essential part of a functional immune system.
Approximately two thirds of the body’s elemental iron are found in the hemoglobin of red blood cells. Other 25% are stored in the proteins ferritin (found in the liver, spleen and bone marrow) and myoglobin (found in muscles), which act as a buffer against iron deficiency. The rest of the body’s iron is a vital component of several enzymes, which play important roles in various chemical reactions including energy-producing redox reactions as well as synthesizing oxygen-binding proteins (hemoglobin and myoglobin) and neurotransmitters.
As a result, appropriate levels of iron in the body are essential for normal growth and development, brain and muscle function, mental concentration, energy metabolism, regulation of the body temperature and for healthy immune system.
The recommended dietary allowances and the tolerable upper intake levels of iron are as follows:
|RDA (mg per day)||Upper Limit (mg per day)|
|Birth to 6 months||0.27 (*)||0.27 (*)||40||40|
|7 – 12 months||11||11||40||40|
|1 – 3 years||7||7||40||40|
|4 – 8 years||10||10||40||40|
|9 – 13 years||8||8||40||40|
|14 -18 years||11||15, pregnant 27, lactating 10||45||45|
|19 – 50 years||8||18, pregnant 27, lactating 9||45||45|
|51 years and older||8||8||45||45|
* Adequate intake as no RDA has been established
People normally lose only small amounts of iron through urine, feces and sweating. However, losses are much higher in menstruating women due to blood loss. Pregnant women also need more dietary iron because they make blood for the baby.
A lack of iron is most common among women of childbearing age. It is estimated that about 10% of menstruating women suffer from iron deficiency. This condition is also quite common in babies and in people with gastrointestinal disorders that impair the absorption of nutrients. Other factors that may contribute to the development of iron deficiency are increased blood loss (e.g., repeated blood donation, colon cancer, heavy menstrual bleeding), endurance exercise and taking too many antacids. In fact, iron deficiency is among the most frequent nutritional deficiencies in the world. Prolonged lack of iron can eventually lead to iron deficiency anemia, a condition manifested by a decrease in the amount of red blood cells. However, men and post-menopausal women are rarely deficient in iron.
Symptoms of iron deficiency in its early stages are difficult to isolate. Symptoms of iron deficiency anemia (late-stage iron deficiency) include a lack of energy and motivation, trouble concentrating, fatigue, muscle weakness, cold hands and feet, shortness of breath when exercising, fast heartbeat, excessive menstrual blood-flow, compromised immune system, brittle nails and hair, sores at the corners of the mouth and on the tongue and, in particularly severe cases, difficulty swallowing.
Too much iron is bad for health. For example, iron overload may cause free radical damage to the body’s organs such as liver, pancreas, heart or lining in the gut and may increase the risk for arteriosclerosis, liver cirrhosis, diabetes and heart disease. Excessive iron can also interfere with the absorption of other nutrients such as zinc, copper, magnesium and calcium. Small children and patients with hemochromatosis (uncontrolled iron absorption leading to iron salts deposits in the tissues) are at an increased risk for iron overdose.
Symptoms of iron toxicity include diarrhea, vomiting blood, dehydration, abdominal pain, metallic taste in the mouth, drowsiness, dizziness, lack of energy, fast and weak pulse, low blood pressure, build-up of fluids in the lungs and bloody stool in children.
Dietary Sources of Iron
Both animal and plant foods are good sources of iron. Animal foods contain the so-called heme iron, which is more easily absorbed, while plant foods contain non-heme iron. Despite the difference in absorption, animal foods contribute only about 15-20% of the dietary iron. The best sources of dietary iron among animal foods include liver (especially the chicken and beef liver), seafood, lean red meats (beef, lamb), chicken and eggs. Plant foods high in iron are legumes (beans, lentils, peas, soybeans), dark leafy greens (spinach, Swiss chard, collard greens, parsley, bok choy, asparagus, mustard greens, leeks, romaine lettuce, Brussels sprouts, broccoli, cabbage), squash, seeds (pumpkin, sesame), nuts (almond, cashew, hazelnut, peanut, pine, pistachio), tomatoes, potatoes, chilli peppers, olives, cocoa powder and dark chocolate. In addition, many cereals are fortified with non-heme iron.
Many multi-mineral supplements also contain iron. Dietary supplements typically contain non-heme iron, which is absorbed less effectively than heme iron from animal sources. However, you should also know that certain nutrients can influence iron absorption. For example, vitamin C can enhance absorption of iron (especially non-heme iron) whereas excessive amounts of vitamin E, copper, zinc, calcium and magnesium may negatively affect iron uptake. In addition, vitamin A deficiency, though quite uncommon, may impair the body’s ability to fully utilize iron when producing hemoglobin, while copper deficiency may impair iron transport to its intended destinations. Other nutrients that can decrease the absorption of iron include polyphenols and phytic acids commonly found in many plant foods.
Iron can also interact with some medications (e.g., levodopa, levothyroxine), reducing their absorption or efficacy, while certain other medications (e.g., proton pump inhibitors) can in turn impair iron absorption. Furthermore, people with arthritis, acute infections, hepatitis, stomach ulcers, inflammatory bowel disease, hemochromatosis or those who receive a blood transfusion should avoid supplements that contain iron.