"Iron is abundant in biology. Iron-proteins are found in all living organisms, ranging from the evolutionarily primitive archaea to humans. The color of blood is due to the hemoglobin, an iron-containing protein. As illustrated by hemoglobin, iron often is bound to cofactors, e.g. in hemes. The iron-sulfur clusters are pervasive and include nitrogenase, the enzymes responsible for biological nitrogen fixation. Influential theories of evolution have invoked a role for iron sulfides, iron-sulfur world theory."

"According to the National Health and Nutrition Examination Survey (NHANES) III, intakes for men generally exceed the RDA, whereas most women consume lower than the RDA. A key point to remember is that the RDA for premenopausal women is 10 milligrams higher than the RDA for men, thus making it more challenging for women in this age group to consume an adequate amount of iron. The ability of the body to absorb and utilize iron from different foods varies. The iron in meat, poultry, and fish is absorbed and utilized more readily than iron in other foods."

"DRI Tables"

"Recommended Dietary Allowances (RDA) - The daily dietary intake level of a nutrient considered sufficient by the Food and Nutrition Board to meet the requirements of 97.5% of healthy individuals in each life-stage and sex group. It is calculated based on the EAR and is usually approximately 20% higher than the EAR. ... Tolerable upper intake levels (UL) - To caution against excessive intake of nutrients (like vitamin A) that can be harmful in large amounts. This is the highest level of daily consumption that current data have shown to cause no side effects in humans when used indefinitely without medical supervision."