popsycal, there are many papers showing a reduced risk of br cancer the longer you bf, but this is a new one to me - it is a very large study (over 110,000 women) and because it was done in a population where longer term breastfeeding is normal, they have enough of a cohort to show an effect.
This cohort shows that bf beyond 2 years protects the mother, which as I say, is a new finding for me, as I had only seen papers looking up to 2 years before now.
There was a good paper about three years ago in the Lancet that took in all the good studies up to that point, and made a calculation about how many breast cancers would be avoided each year (IIRC) if x per cent of women breastfed for x months longer than they do now.
I think it's crazy to deny that children can benefit from breastfeeding at whatever age - I mean, why wouldn't they? It's like saying 'I don't believe good quality food and drink is beneficial to a baby over x months - show me the proof!'.
Daft.
If he doesn't understand why it's daft then maybe he will accept the cancer stuff.
This is pre-menopausal cancer, BTW.