I do not believe that the sodium does anything at all.  High sodium
occurs when a mother is weaning a baby from the breast, or in mastitis.

Many health professionals admit dehydrated babies to the hospital and
then test the mother's milk because of the baby's high serum sodium.
The mother's milk has a high sodium and this is supposed to explain the
problem.  It does not.

The problem is that the baby is not breastfeeding.  And if he is not
breastfeeding, the mother's body interprets this as "weaning" and the
milk sodium rises.

Babies fed cow's milk are getting 50-55 meq/l and they only ran into
problems if they started getting gastroenteritis.  Then they got
hypernatremic.  When tested, mother's milk rarely if ever gets as high
as that.

This mother should breastfeed.  She needs a good start and to know how
to know the baby is breastfeeding (not just sucking).  Testing the
breastmilk is irrelevant and might just frighten her.  Sodium in
colostrum tends to be high as well.

Jack Newman, MD, FRCPC