Most breastfeeding women are told by their health care provider to continue taking prenatal vitamins after they give birth. A woman's requirement for iron while breastfeeding is low, yet prenatal vitamins contain a large amount of iron. The purpose of this study is to see if breastfeeding women are getting too much iron when taking prenatal vitamins.

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:

1. To compare markers of lipid oxidation (urinary isoprostane) and DNA damage (urinary 8-OHdG (urinary 8-hydroxy-2'-deoxyguanosine)) among 3 treatment groups: (iron given between meals (27 mg daily, in a multivitamin-mineral supplement), iron given with meals (27 mg daily, in a multivitamin-mineral supplement) and multivitamin-mineral supplement with no iron, given between meals) at the beginning and end of 3 months of treatment in 114 lactating women.
2. To compare hemoglobin and iron status (ferritin, transferrin saturation, and hepcidin) before and after treatment among the three treatment groups described above.

Inclusion Criteria:

• Women less than 4 weeks postpartum
• 18 years of age or older
• Took prenatal vitamins for at least 3 months during pregnancy
• Successfully initiated breastfeeding

Exclusion Criteria:

• Anemic (Hgb < 110 g/L)