http://scienceofmom.com/2014/08/08/caffeine-and-breastfeeding/
From the webapge:
A few weeks ago, I wrote about the safety of caffeine in pregnancy, and several readers wanted to know about the postnatal effects of caffeine – how mom’s caffeine intake might affect her breastfed baby. I promised to take a look at the literature and report back, and so here we are.
When you drink a cup of coffee, how much caffeine ends up in your breast milk?