>>Does anyone have information on the role of heavy exercise (running several
miles every day or two) on lactational amenorrhea and infertility?<<

Catherine,
Other than the nursing and related hormonal issues that you already know:

I don't think that running that is the issue, but rather the amount of body
fat. Some women athletes, especially marathon runners and Olympic-level
athletes, often work out so much that they become lean, mean, athletic
machines with less than normal body fat. A woman's body requires a minimum
amount of fat in order to cycle and ovulate, most likely due to the fact that
low fat levels historically signified starvation, and the body in turn
rejected starting a pregnancy with a poor probably outcome.  Please forgive
me if you already know this! :-)
-Lisa Marasco, IBCLC
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