A long-term study has pointed to a link between breastfeeding and intelligence. The research in Brazil traced nearly 3,500 babies, from all walks of life, and found those who had been breastfed for longer went on to score higher on IQ tests as adults.

Experts say the results, while not conclusive, appear to back current advice that babies should be exclusively breastfed for six months.

But they say mothers should still have a choice about whether or not to do it.