There is one study done a few years ago which showed that the quantity
of manganese in formula is much greater than in breastmilk.

Davidsson L, Cederblad A, Lonnerdal B, Sandstrom B.  Manganese
absorption from human milk, cow's milk and infant formulas in humans. Am
J Dis Child 1989;143:823-7

These were not done in mothers who had particularly high levels of
manganese in their blood or any reason to think so, but the authors
expressed concern about the CNS effects of the amounts of manganese the
babies fed formula would be getting.

Jack Newman, MD, FRCPC