Iron is very toxic in large amounts. In just 3 to 4 days, toxic levels of iron can cause death. In a severe overdose, iron quickly destroys the lining of the intestinal tract. It may lead to holes in the intestine. Free iron ions in the bloodstream destroy the lining of the blood vessels (endothelium). This leads to irreversible shock. Too much iron can also cause severe liver damage.
Iron supplements, including prenatal and children's vitamins, often come as brightly colored tablets. Young children find these attractive. They may attempt to eat an entire bottle. Because iron is very toxic and large overdoses can be fatal, it's important to store iron supplements out of the reach of children. Close to 100% of iron poisonings happen in children. Iron is the leading cause of fatal poisoning in children.
Iron can also cause side effects at normal doses. These can include constipation or black stool. Taking a stool softener may help.
Taking daily doses of iron above the recommended amount may cause iron to build up in your body. This can lead to iron overload. This harms the liver and causes cirrhosis. It can also damage the heart, pancreas, pituitary gland, and other organs. This condition is called acquired hemochromatosis.
Taking in too much iron is also linked with heart disease. Studies are also looking at whether too much iron plays a role in some types of cancer.
Many blood diseases can cause anemia. Taking iron supplements can mask these issues. This can cause them to go undiagnosed. Some blood diseases, if treated with iron, may cause iron overload. They include:
- Sickle cell anemia.
- Glucose-6-phosphate dehydrogenase deficiency.
- Hereditary spherocytosis.
- Hereditary elliptocytosis.
- Pyruvate kinase deficiency.
- Acquired or genetic hemochromatosis.
- Thalassemia.
Iron supplements often contain tartrazine or sulfites. People who are allergic to aspirin have a higher sensitivity to tartrazine. People who have asthma are more likely to be allergic to sulfites. People with these conditions should talk to their doctors before taking an iron supplement.
Iron interacts with many medicines. Antacids can decrease how much iron your body absorbs. So can cimetidine, a medicine that blocks the production of stomach acid. This means iron supplements won't work as well. Ascorbic acid (vitamin C) increases how much iron is absorbed. The antibiotic chloramphenicol increases the levels of iron in your body.
Any medicine in the tetracycline family will bind with iron. This will decrease the absorption of both the medicine and iron. Iron also interferes with levodopa, methyldopa, etidronate, levothyroxine, penicillamine, and quinolone antibiotics. Iron decreases how well these medicines work.
Eggs, dairy foods, and drinks such as coffee and tea can decrease iron absorption. You shouldn't take iron within 2 hours of eating these foods. Calcium, fiber, tannin (found in tea), soy protein, and oxalic acid (found in some vegetables) can keep your body from absorbing iron.