While breastfeeding is often recommended by doctors to help protect newborns from infections and diseases, the question of whether breastfeeding actually leads to cognitive benefits for infants isn't so well settled.
Despite previous studies indicating that breastfeeding has a positive impact on children's intelligence – which researchers say could be due to nutrients in breast milk – a new study now suggests that there are no long-term cognitive benefits to breastfeeding.
Using data from the Growing Up in Ireland longitudinal study, a team from University College Dublin studied 7,478 children, whose cognitive abilities were assessed at ages three and five.
During the assessments, children were tested on their problem-solving and vocabulary skills, and were also evaluated in terms of their behaviour, including assessing their emotional symptoms, hyperactivity, and relationships with others.
The researchers found that after accounting for socio-economic variables such as parents' education and income, there was no strong evidence to suggest that children who had been breastfed as babies demonstrated cognitive benefits over babies who hadn't.
"[W]e didn't find any statistically significant differences between children who were breastfed and those who weren't, in terms of their cognitive ability and language," one of the researchers, Lisa-Christine Girard, told Katie Forster at The Independent.
But on one measure, the results did show a contrast.
"We did find direct effect of breastfeeding on a reduction in hyperactive behaviours when the children were three years old," says Girard. "This wasn't found at five years, suggesting there may be other factors that are more influential as children develop."
In other words, it's possible that the notion that breastfeeding confers a benefit to children's intelligence hasn't successfully accounted for all the parental, lifestyle, and other socio-economic factors that can also influence a child's development and upbringing.
"I think [the study] fits well in the body of literature that long-term benefits of breastfeeding look a whole lot smaller or non-existent if you properly control for your confounding variables," statistician Brooke Orosz from Essex County College in New Jersey, who was not involved with the study, told CNN.
"The easy question – do kids who are breastfed have better outcomes? The answer is yes. The difficult question is: is it breast milk that improves their brain, or is it that growing up with parents who are better educated and have better incomes makes a difference?"
While the new study might not be able to provide a definitive answer on that issue, the results do seem to suggest that socioeconomic factors could have played a part in skewing previous data – but Girard's team doesn't expect this to be the end of the discussion.
"This has been a debate for over 100 years, and we're working hard to understand the complete picture," she told Allison Aubrey at NPR.
In any case, while researchers will continue to investigate the link – if any – between breastfeeding and developmental benefits, scientists say the new study shouldn't dissuade anybody who wants to breastfeed from doing so, given the commonly accepted health and nutrition advantages.
Of course, not every mother is able to breastfeed, due to a range of conditions that make breastfeeding difficult or impossible for some – but for women who don't experience those complications, the advice from physicians is firm.
"There's a strong body of evidence to support that breastfeeding is one of the healthiest things we can do to support children's immune systems," paediatrician Ellie Erickson from Duke University, who wasn't involved with the study, told NPR.
On that issue, at least, it's a point that the study authors are in complete agreement with.
"The medical benefits of breastfeeding for both mother and child are considered numerous and well documented," the researchers write in their paper.
"[T]hese findings do not contradict the many medical benefits afforded to both mother and child as a result of breastfeeding."
The research is published in Pediatrics.