Iron is an essential mineral in the diet, and is a crucial component of hemoglobin, the protein in red blood cells that carries oxygen throughout the body. Dietary iron is present in two forms. Heme iron is bound within a ring-shaped molecule called porphyrin. It is found mainly in red meat. Non-heme iron is found in both plants and animals. Its absorption is aided by vitamin C.
The hormone hepcidin regulates the body’s balance of iron. The function of hepcidin is to suppress absorption of iron. When the body’s iron stores are high, levels of hepcidin increase, and iron absorption decreases. When iron stores are low, iron absorption increases. For this reason, it is uncommon to suffer from too much iron in the diet. However, there are some situations where iron toxicity or iron overload can occur.
Iron toxicity can be caused by taking high doses of iron supplements for prolonged periods of time, or by taking a single overdose. Single doses as low as 10 to 20 mg/kg can cause some symptoms of iron toxicity. Medical attention is required at doses greater than 40 mg/kg, and more than 60 mg/kg can be lethal.
Excessive iron can be damaging to the gastrointestinal system. Symptoms of iron toxicity include nausea, vomiting, diarrhea and stomach pain. Over time, iron can accumulate in the organs, and cause fatal damage to the liver or brain.
Toxic cellular effects occur as well. Oxidative phosphorylation and mitochondrial function can be hindered by large amounts of iron, leading to death of cells. Iron toxicity primarily affects the liver, but other organs and the blood may also be affected.
Metabolic acidosis occurs due to fluid loss, dilation of the blood vessels and an anaerobic metabolism due to inhibition of oxidative phosphorylation.
Iron overload is a condition that can develop over time, particularly in people who receive many red blood cell transfusions, such as patients with myelodysplastic syndrome, thalassemia, or sickle cell disease.
When the body absorbs too much iron and its iron-binding proteins are saturated, the result may be a disorder of iron overload, known as hemochromatosis. The illness causes a bronze tint to the skin. However, it also brings about more serious effects of the disorder on the organs. Deposits of iron in the liver can cause cirrhosis, while in the pancreas, it may lead to diabetes.
Hemochromatosis is a genetic disorder of iron metabolism. It does not result from excess iron intake by a genetically normal individual. People with hemochromatosis can reduce the risk of illness due to iron overload by reducing their intake of iron-rich foods like red meat, and donating blood frequently. They should also avoid using iron cookware, and should not combine foods high in vitamin C with foods rich in iron.
High iron levels have been shown to cause cancer in humans and animals. High levels of heme iron in the diet are associated with an increased risk of colon cancer. Heme iron may lead to formation of carcinogenic N-nitroso compounds in the digestive tract.
Reviewed by Liji Thomas, MD