Even though iron requirements are much lower for lactating women than for pregnant or non-pregnant, non-lactating women, and iron stores during lactation are often high due to release of iron from the additional maternal erythrocytes produced during pregnancy, iron supplements are often taken by lactating women in the U.S. Many studies have shown that higher iron status is associated with higher risk of certain chronic diseases (e.g. cancer and cardiovascular diseases). The overall goal of this proposed study is to understand the potential for oxidative stress due to iron supplementation, and possible mechanisms for these effects, and to identify safe and efficacious ways to ensure adequate iron status during lactation. The specific aims are: