I have no studies about this, just a personal opinion and lots of
anecdotal evidence.
        When I talk to mothers of newborns, particularly babies who have
problems sleeping as much as their parents think that they should at
night, I always remind them that a baby's need for contact, touch and
nursing (breastfeeding for non-Americans) is a 24 hour need.  If for some
reason the baby cannot or does not get enough during the day they will
compensate at night.  I also think that there is some hormonal influence
of night nursing.  We do know that it is frequent night nursing that
suppresses menstruation etc.  It seems to me that slightly older babies,
and their mother's bodies, are probably still at least partly regulated
by these mechanisms.  As a result co-sleeping and frequent night nursings
will be very important in maintaining a supply.

Sarah

Sarah Friend Barnett, LLLL,  IBCLC
Bronx, NY