I'm a retired La Leche League leader. I believe there are many benefits to breastfeeding, but any difference in IQ is relatively small (original claims were 6-10 points, more recently it has been downgraded to a slightly more conservative number) and may be due to the intelligence of the parents more than the milk itself. In the US, smarter parents are more likely to choose to breastfeed.
Four or five points may push a gifted child into HG or an EG child into PG territory, but it will not make an average kid into a genius. Otherwise, people of the US born in the last hundred years or so would be the stupidest people in history.
We practice extended breastfeeding here.
