Iron metabolism is shaped by iron's status as an essential nutrient for which there is no mechanism for excreting any excesses that may accumulate in the body.
A 70 kilogram man contains about 3.7 grams of iron.
Most of this, almost 70%, is present in hemoglobin.
Most of the rest, almost 30%, is stored as ferritin.
The remainder is in myoglobin, the cytochromes, other hemoproteins, the iron-sulfur proteins of respiration, and so forth.
Iron is very active chemically.
For example, it
binds nonspecifically to many proteins, with deleterious consequences to their structures.
acts catalytically in assorted oxidation reactions, such as peroxidation of unsaturated lipids in cellular membranes.
Because of this it is always found in bound form.
It therefore does not get excreted. Iron is lost from the body only by processes such as
bleeding
sloughing of cells
menstrual flow
transfer to a developing fetus.
The body's iron content is regulated by controlling absorption.