Lynn,
exogenous means from the outside.  as opposed to endogenous, which means
generated within.
I was using exogenous as meaning from the outside of the mother-baby
relationship, iron that was not from the mother's milk.
        Lactoferrin is an iron scavenger.  Any free iron in the baby's
gut that was not absorbed into the baby's intestinal villi is grabbed by
lactoferrin and flushed out of the body.  Bacteria cannot then get the
iron away from the lactoferrin.  Many of the nastiest germs need iron in
order to reproduce and grow.  If you think of lactoferrin as a sponge
that is designed to pick up about half the iron in breastmilk (the amount
that the baby does not absorb), then you can see how adding more iron to
the baby's digestive system will fill the sponge.  Once that sponge is
full, any additional iron is left for the bacteria, and the baby is
vulnerable to illness.  This is only one of the known functions of
lactoferrin, it also interferes with bacterial carbohydrate metabolism
(germs eating sugar) which is how it prevents cavities.  But again, all
the functions of lactoferrin are dependant on it's unsaturated state.
This is a complex chemical that we have just begun to study.
        An important concept here is that of bioavailability-  It's not
how much you take, it's how much you can absorb and use.  Human milk iron
is 49% bioavailable, that's a huge bioavailability.  Iron filings
(elemental iron) are 2% bioavailable.  That's the form that is in abm.
Iron salts are slightly more bioavailable.  Meat is a highly bioavailable
source of iron.  So it is a different thing to offer a breastfed child a
few shreds of beef than to feed a half cup of iron (filing or salt)
fortified cereal.
        Hope this clears up your questions, if not, ask again.  This is
complicated stuff that we are just beginning to understand.  My own
personal bias is to leave kids on breastmilk alone until they are
grabbing the food on the table and stuffing it in their own mouths.  Then
offer the child small bits of whatever the family is eating, sans the
major allergens- especially cow milk.
--
Catherine Watson Genna, IBCLC  NYC  [log in to unmask]