The high mortality of old age is associated with a high concentration of iron in the tissues, just as the high mortality of young infants is associated with a high concentration of iron. As the infant's iron is diluted by growth, mortality decreases.
Infectious disease and leukemia, which have been associated with excess iron, are highest in childhood and old age. June Goodfield's book gives a nice summing up of the early research on the relation of iron metabolism to cancer and immunodeficiency:
"... in essence the immunological system has evolved with the ability to survey, and recognize, and utilize -I don't know exactly what. But this ability is expressed as a capacity to survey metals and, in particular, iron. It goes in as ferrous iron, and is then rapidly oxidized into ferric iron. This is then bound to a protein, transferrin, and so is carried into the bone marrow and thus given to the early red blood cells, which need it for the blood cycles. But Iron is also bound to a second protein, ferritin, which is a storage protein .... When red cells get old they break down in the spleen and are eaten up by the macrophages, which then make ferritin. (It enters the storage pool again.) Then there is the third protein, lactoferrin, which Is synthesized by polymorphs, the white cells, and is present in milk and in our secretions. The amount we excrete per day is absolutely minimal. You can only shove it in; you can't push It out. Now if, for some reason or other, there is too much iron around, the macrophages go and mop it up. And as far as I'm concerned, in the diseases we've been studying - Hodgkin's. leukemias - there is an abnormality in the lymph nodes and the macrophages in regard to the intake, or the handling, of the iron... I have a simple scheme, again probably too simple.
Lymphocytes go and are caught where there is an excess of iron. A malignant cell, like a virulent cell, behaves like a virulent bacterium. It becomes capable of sucking up iron avidly and utilizing it... if the tumor cells eat up the signal - iron – the lymphocytes won't go there. The tumor will grow undisturbed because the lymphocytes have not had a signal to move toward it.”
As I mentioned above, I think some of the excess iron accumulates in the form of age-pigment, and that this material serves to keep glycolysis running as an emergency energy source. Glycolysis produces lactic acid, which is characteristic of tumor metabolism even in the presence of oxygen, and lactic acid has its own direct effects on immunity. – Ray Peat ‘Mortality Again’