What is Iron?
Iron is an essential dietary mineral present in a wide variety of foods, but the iron found in plants (notably grains and legumes) is less bioavailable than the iron found in meat (in the form of heme). Its main role in the body is as a critical part of hemoglobin, red blood cells' oxygen-carrier, and a deficiency in iron leads to poor oxygen transport (anemia) In addition, iron is a cofactor for many enzymes. It is the double-edged sword of the nutrient world. On the one hand, many people have insufficient levels, but on the other hand, iron overload can make it toxic to a wide variety of cells. Iron deficiency is the only reason to consider iron supplementation, though getting more iron through foods should be preferred when possible. For people who already have enough iron, taking an iron supplement has no proven benefit; on the contrary, it can lead to iron overdose.
What are Iron's benefits?
A lack of iron will tend to produce fatigue, depression, impaired cognitive function, restless leg syndrome, and other adverse effects. The correction of iron deficiency will tend to improve symptoms, and even among people who aren't anemic, there may be a need for more than the bare minimize to produce optimal amounts of hemoglobin and reap the benefits of greater oxygen deliver, though more research is needed, and the effect is probably limited to people with low iron levels by conventional standards. Iron deficiency is fairly common and a great number of factors negatively affect iron status, so iron supplementation and iron-rich diets can be expected to benefit many people.
What are Iron's downsides?
Supplementation can produce nausea, headaches, and other symptoms. As already mentioned, iron overload is a serious health risk.