Iron
Iron is essential to all organisms, except for a few bacteria.
Iron deficiency is the most common mineral deficiency in the world, causing anemia in men, women and children.
Iron distribution is heavily regulated in mammals, both as a defense against
bacterial infection as well as the potential biological toxicity of iron. The
iron absorbed from the duodenum binds to transferrin, and is carried by blood to
different cells. There it gets by an as yet unknown mechanism incorporated into
target proteins.
Good sources of dietary iron include meat, fish, poultry, lentils, beans, leaf
vegetables, tofu, chickpeas, black-eyed pea, strawberries and farina.
Iron provided by dietary supplements is often found as Iron (II) fumarate. The
RDA for iron varies considerably based on the age, gender, and source of dietary
iron (heme-based iron has higher bioavailability).
Metallic iron filings are added to some breakfast cereals and listed in the
ingredients as "reduced iron" ("reduced" referring to redox chemistry). If the
cereal is crushed, the iron filings can be separated with a magnet.
Excessive iron is toxic to humans, because excess ferrous iron reacts with
peroxides in the body, producing free radicals. Iron becomes toxic when it
exceeds the amount of transferrin needed to bind free iron. In excess,
uncontrollable quantities of free radicals are produced.
Iron uptake is tightly regulated by the human body, which has no physiological
means of excreting iron and regulates iron solely by regulating uptake. However,
too much ingested iron can damage the cells of the gastrointestinal tract
directly, and may enter the bloodstream by damaging the cells that would
otherwise regulate its entry. Once there, it causes damage to cells in the
heart, liver and elsewhere. This can cause serious problems, including the
potential of death from overdose, and long-term organ damage in survivors.
Humans experience iron toxicity above 20 milligrams of iron for every kilogram
of weight, and 60 milligrams per kilogram is a lethal dose. Over-consumption of
iron, often the result of children eating large quantitities of ferrous sulfate
tablets intended for adult consumption, is the most common toxicological cause
of death in children under six. The DRI lists the Tolerable Upper Intake Level
(UL) for adults as 45 mg/day. For children under fourteen years old the UL is 40
mg/day.
If iron intake is excessive iron overload disorders can sometimes result, such
as hemochromatosis. Iron overload disorders require a genetic inability to
regulate iron uptake; however, many people have a genetic susceptibility to iron
overload without realizing it and without knowing a family history of the
problem. For this reason, people should not take iron supplements unless they
suffer from iron deficiency and have consulted a doctor. Blood donors are at
special risk of low iron levels and are often recommended to supplement their
iron intake.
The medical management of iron toxicity is complex. One element of the medical
approach is a specific chelating agent called deferoxamine, used to bind and
expel excess iron from the body in case of iron toxicity.
