Iron is a mineral essential for the human body, and its primary function is in the synthesis of hemoglobin.
However, iron comes in many forms. The iron in cast iron cookware is "elemental iron" in its atomic state. Even if a tiny amount of iron leaches into food during cooking, forming inorganic iron, it is difficult for the human body to absorb. The type of iron that can be absorbed by the body is "ferrous iron" in its ionic state, also known as heme iron. Furthermore, there are individual differences in how the human body absorbs iron, so very few people can actually supplement their iron intake by cooking with an iron pot.
In an era of material scarcity, for those with iron deficiency, iron leaching from iron pots could help prevent anemia. But in today's affluent world, eating half a pound of animal liver provides far more iron than cooking with an iron pot. Moreover, cooking with an iron pot increases the loss of antioxidants. Relying on an iron pot to reverse iron-deficiency anemia or solve other health problems is simply not realistic.