Iron is a trace mineral that is found primarily in the hemoglobin of red blood cells. It is also found in relative abundance within the myoglobin of muscle cells, where it is required for oxygen and carbon dioxide transport. Iron is also used in several enzymes and energy-producing systems in the body; it is also essential in the production of the neurotransmitters dopamine, norepinephrine, and serotonin. Most often, a deficiency of iron leads to a particular form of anemia known as microcytic/ hypochromic anemia. Iron deficiency can have serious, and often times, damaging consequences; even resulting in death. Conversely, it is also one of the most frequent causes of poisoning-related deaths in small children. 
Iron supplementation is quite controversial; typically menstruating women are the only group of people that need iron replacement on a continual basis because of regular blood loss. Men rarely require iron supplementation and interestingly, men with higher intakes of iron have an increased risk of heart disease. If you are unsure about your need for iron supplementation it is recommended that you first consult with your physician.
Iron is found abundantly in animal products, as well as certain vegetables. Red meats contain the highest percentage of iron content found in all animal sources, while dark green leafy vegetables have the highest iron content of plant origin.
Iron absorption from foods varies greatly depending on the form of iron contained in a given food source. Typically, food sources contain heme iron or non-heme iron; heme iron is better absorbed (roughly 20 to 23 percent) while non-heme iron is absorbed at some 15 - 20%.  Animal sources of iron contain both of these forms. Plant sources only contain non-heme iron. If plant sources are boiled, steamed, or cooked, the availability of their iron content is increased. However, if stored or refrigerated for an extended period, these preparation methods negate iron bioavailablity. 
Regardless of how the food is cooked or what type it is (or the amount of iron it contains), the body will typically absorb a maximum of 15% of the iron ingested. This is highly variable. Factors influencing iron absorption include individual health status, physiological need. 
As mentioned earlier, iron is necessary for oxygen and carbon dioxide transport in the body; specifically within the electron transport chain (an intercellular energy production system), the enzymes of the Krebs cycle (a major energy production cycle), and in neurotransmitter development. 
Iron is a primary form of treatment in various health conditions. The broadest application of iron is in the treatment of anemia and other iron deficient states. Iron is mandatory for the production of red blood cells and therefore is applied in any condition in which iron levels are suboptimal and blood quantity is affected. [6, 7]
Iron is vital for early childhood development. Deficiencies are associated with impaired neurologic and behavioral development, with multiple organ systems being affected.  Iron deficiency during pregnancy leads to abnormal developments during gestation and impacts the health of the infant. There is also an increased mortality rate of iron-deficient mothers following birth. 
Newer research is investigating the use of supplemental iron in attention-deficit hyperactivity disorder (ADHD); it appears that supplementation with iron improves symptoms of this condition. 
Iron has been used empirically for fatigue in many patient populations despite normal levels. Research findings point to the effectiveness of moderate iron supplementation in non-anemic women by improving symptoms of fatigue. 
The RDA has established dosage guidelines for iron in several different age groups:
Infants and Children:
- Infants 6 months and under: 0.27 milligrams per day
- Infants 7 to 12 months: 11 milligrams per day
- Children 1 to 3 years: 7mg/day
- 4 to 8 years: 10 mg/day
- 9 to 13 years: 8 mg/day
- Boys 14 to 18 years: 11 mg/day
- Girls 14 to 18 years: 15 mg/day
- Men age 19 and older: 8 milligrams per day
- Women age 51 and older: 8 milligrams per day
- Women 19 to 50 years: 18 mg/day
- Pregnant women: 27 mg/day
- Lactating women: 10 mg/day for ages 14 to 18 years, 9 mg/day for ages 19 to 50
All other indications for iron supplementation should be under the supervision of a physician.
Iron deficiency is a relatively common condition, with dire consequences in the young and treatable circumstances in adults. Deficiency of iron, primarily caused by dietary factors, is most common among vegetarian women who may not consume enough iron in their diets to counter regular blood loss through menses. Pregnant women are also at higher risk of becoming iron deficient, due to the increased blood volume and requirement for this mineral during gestation. Iron supplementation in pregnancy is very common.
Men are rarely iron deficient; they may become deficient following certain types of surgeries or chronic disease, in which blood loss is the key contributing factor. Another group that may become iron deficient (from factors other than iron absence in diet or disease) are competitive athletes. Certain athletes may suffer from exercise-induced hemolysis (destruction of red blood cells) and intestinal blood loss for unknown reasons. 
At doses within the abovementioned recommended ranges, side effects are rare. However, doses larger than 45 milligrams per day may lead to symptoms of abdominal pain, constipation, nausea, and vomiting in the short term. Normal doses of iron are known to cause constipation and gastrointestinal upset. Long term overuse of iron leads to a condition known as hemosiderosis, in which iron is stored throughout the bodily tissues in excessive amounts. Acute overdosage of iron can lead to vomiting, diarrhea, cardiovascular and metabolic toxicity, and death.
Excessive levels of iron are theorized to influence certain disease conditions. Numerous studies show a link between iron and cancer; however, this parallel remains uncorroborated. [12-14] There may also be an association between iron intake and risk of heart attack and/or coronary heart disease. [15, 16]
Supplementation with iron must be carefully considered; appropriate laboratory testing should be performed prior to ingesting any supplemental forms of iron. Iron is one of the few supplements available without prescription that carries relatively high health risks if used improperly.
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