I'll just add to this discussion something I wrote somewhere else, but lost it...

There have been conflicting studies on vitamin K.

One study came out and showed an increased risk of childhood leukemia.
Another study came out and dismissed it.
Another study came out and said yes there is a link, but not as bad as we thought.

It's all very confusing. So I asked my teacher and she basically said that if you are going to breastfeed and have had a normal healthy birth, then you might like to choose not to have it. But if baby is bruised or you have had a traumatic birth, forceps etc, you would probably choose to have it.