As it turns out, the largest pediatric practice in the area had started recommending iron supplements for exclusively breastfed babies, starting soon after birth.
In my training I'd learned that most healthy, full term babies have iron stores that last for at least six months, and that the iron in breastmilk is very well absorbed. So, I got out my books. Here's what the textbook Breastfeeding and Human Lactation had to say:
Iron supplementation is not usually needed and may in fact be detrimental to the breastfeeding baby in the first half-year after birth. Excess iron tends to saturate lactoferrin and thereby diminish its antiinfective properties.
The book referenced this important study on iron supplements and breastfed babies, which found that iron supplementation for exclusively breastfed babies actually resulted in slower growth, smaller head circumference, and more diarrhea than babies who were not given iron supplements.
Now, before we go any further, I need to say that iron deficiency is a serious problem, and iron supplementation is critical if a baby is iron deficient. For more on the topic, see this page on kellymom.com, and of course consult with your pediatrician for medical advice suited to your own situation.
Why is giving iron supplements to exclusively breastfed babies - who are not iron deficient - a problem? The theory has to do with the function of lactoferrin, an important component of breastmilk. Lactoferrin has the job of binding with iron in the baby's gut and getting it absorbed into the baby's system. In doing so this component of breastmilk deprives bad bacteria (E.coli, Staphylococcus, etc.) of their favorite food source: iron. If extra iron is given to the baby, the lactoferrin in breastmilk gets "overwhelmed" and can't bind with all of the iron. This leaves extra iron in the system to fuel those bad bacteria. There is even some suggestion that extra iron reduces the ability of lactoferrin to bind with the iron in breastmilk, resulting in the baby getting less of the available iron. In this case, less is more.
So, what happened with the pediatric practice in our town? My son is a patient at this practice and at his 3 year check up (pictured in this post) I expressed my concerns about the iron supplementation policy. My son's doctor listened and asked for references for the concerns I raised. I dropped off the study and references a few days later, and our doctor said that he'd bring it up with the other pediatricians in the practice. Shortly after, he called to let me know that the practice had decided to change their policy and are now not recommending iron supplements for exclusively breastfed babies unless they are iron deficient.
That's why I love our pediatrician.