While most people take iron safely, excessive amounts of iron can be toxic. Symptoms may range from fatigue to life-threatening shock. The signs and symptoms of acute iron toxicity are different than those of chronic toxicity. A one-time massive overdose of iron can be fatal within 2 days, while long-term overingestion typically causes more subtle, progressive symptoms.
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Chronic Iron Overload
Multiple doses of IV iron therapy or chronic overingestion of oral iron supplements can eventually damage a variety of organ systems. The most common symptom of iron overload is fatigue. Other signs and symptoms include gray or brown skin discoloration, an enlarged liver or spleen, abdominal pain, congestive heart failure, an irregular heart rhythm, insulin dependent diabetes, joint aches, decreased sex drive, impotence, infertility, irregular menstrual periods, depression, mood swings and hair loss.
Acute Iron Overdose
Within 30 minutes to 6 hours after a large overdose of iron, a person may experience abdominal pain; vomiting, including the vomiting of blood; diarrhea; black, sticky stools; irritability; lethargy; or shock. In severe cases, progression to rapid breathing, fast heart rate and coma can occur. Between 6 to 24 hours later, symptoms may seem to settle down, but soon thereafter heart toxicity -- leading to low blood pressure, fast heart rate, pale appearance and shock -- may occur in the most serious cases.
Likelihood of Overdose
The total number of mg (milligrams) of an iron supplement is not the same as the amount of elemental iron it contains. The toxicity of iron depends on how much elemental iron is ingested. For instance, a 200 mg pill of the common supplement ferrous iron sulfate contains 65 mg of elemental iron, not 200 mg. A common dose of iron is 20 to 30 mg of elemental iron, which is often the amount found in a daily supplement. For comparison, the recommended dietary allowance of iron for healthy adults ranges from 8 to 18 mg.
When to Seek Medical Treatment
Up to 20 mg/kg of elemental iron is unlikely to be acutely toxic. For example, for a 150 pound (68 kg) woman, ingesting 20 mg/kg would equal 1,360 mg of elemental iron, far above recommended doses. So a single dose of 100 mg of elemental iron would not be toxic. However, in the case of any large overdose of iron, particularly if symptoms develop, one should seek medical attention immediately, as it can be fatal within 48 hours. In addition, any symptoms of chronic iron overload should prompt a visit to the doctor, as early diagnosis and treatment may improve the outcome.