The Institute of Medicine sets the upper tolerance for iron supplements, which is the highest daily dose that appears to be safe, at 45 milligrams per day. Taking more than 45 milligrams per day can lead to digestive problems such as nausea, vomiting and constipation.
Iron supplements should always be kept in childproof containers because a single large dose of iron (over 60 milligrams) can cause serious iron poisoning in children under the age of five years. Seek emergency care if you think a young child might have taken a large dose of iron.
Iron Overload Disease
Hemochromatosis is a condition that causes too much iron to be stored in the liver and other organs. It isn't caused by taking too much iron, but people who have it are unable to remove any extra iron that their bodies don't need.
It's more common in males than females and might lead to organ damage if left untreated. People who have hemochromatosis must watch their iron intake. They may also take medication or have blood removed occasionally to reduce iron build-up.
It's unlikely you'll get too much iron from eating a normal diet. Foods high in iron include red meats, organ meats, dark green vegetables, legumes and iron-fortified foods. The iron found in animal-based foods is called heme iron and is easier to absorb than the plant-based form called non-heme.
Institutes of Medicine. "Daily Reference Intakes: Elements." Accessed September 17, 2012. http://iom.edu/~/media/Files/Activity%20Files/Nutrition/DRIs/DRI_Elements.pdf.
Medline Plus. "Hemochromatosis." Accessed September 17, 2012. http://www.nlm.nih.gov/medlineplus/hemochromatosis.html.
Natural Standard. "Iron." Accessed September 17, 2012. http://naturalstandard.com.
Office of Dietary Supplements, National Institutes of Health. "Dietary Supplement Fact Sheet: Iron." Accessed September 17, 2012. http://ods.od.nih.gov/factsheets/Iron-HealthProfessional.
The Children's Hospital of Philadelphia Poison Control Center. "Iron Poisoning." Accessed September 17, 2012. http://www.chop.edu/service/poison-control-center/tox-talk/iron-poisoning.html.