goingnowhere.....for mothers and babies, or both?
Yes, there is evidence, and for both, too.
But it can never be strong enough as 'proof', because it is mainly epidemiological (get a sample of a zillion people, see what has happened to them, then look at certain factors - in this case, breastfeeding - and see if there's a difference between what happened to them, related to these factors. Do your best to control for other stuff eg with heart disease, smoking, or heredity, or adult diet. Crunch the numbers. See what comes out).
Kramer's bf research was the 'highest' form of research, the randomised controlled trial, where you follow different samples, where the only different thing is the intervention - in his team's case, breastfeeding promotion, which one sample had and the other one didn't.
On the heart disease thing, this report is quite good, and clear:
www.webmd.com/heart-disease/news/20090421/breastfeeding-cuts-moms-heart-risk
It shows that in individuals, the effect is small, but of course over a population, the effect will be larger and will save lots of money.