"Breastfeeding has no benefit over bottle feeding when it comes to a child's IQ," the Daily Mail says, reporting on the results of a study that found no significant link between breastfeeding and increased intelligence.
Researchers assessed the intelligence of children involved in the Twins Early Development Study between the ages of two to and 16, testing them 9 times over the course of the study.
They found a small increase in the average IQ of breastfed girls compared with bottle-fed girls at the age of two, but this did not affect boys. They found no differences in average IQ between those fed by breast or bottle in later years.
The idea that breastfeeding might improve IQ is based on the idea certain proteins only found in human breast milk could be important for developing nerve cells.
Previous studies have reported that breastfeeding improves children's intelligence. However, it is possible that these older studies were not sufficiently rigorous to get a reliable result.
While breastfeeding may not be a brain booster, it does bring physical health benefits, such as improved immune protection against infection.
Read more about the physical health benefits of breastfeeding.
Still, the results of the study should reassure women who are unable to breastfeed for health reasons. As the lead author puts it, "Being bottle-fed as an infant won't cost your child a chance at a university degree later in life."
The study was carried out by researchers from the University of London and King's College London. We currently do not have information about who funded the study.
It was published in the peer-reviewed journal PLOS One.
The study was covered accurately by the UK media, and most news stories included reminders that breastfeeding is likely to have other important health benefits.
Cohort studies allow researchers to collect a lot of data about a large group of people, which they can then use to look for links between different factors – in this case, whether breastfeeding has any effect on children's IQs over time. But this type of study cannot prove one factor directly causes another.
The researchers used data from the study to construct a model of the children's IQs over time, based on nine assessments of their intelligence carried out from ages 2 to 16.
The researchers looked at whether there were differences between the IQs of children who had been breastfed and those who had not. They looked for differences at the start of the study and at how the children's IQs changed as the study progressed.
Based on previous studies, the researchers thought they might find that breastfed children had a higher IQ at two years old, and the difference between the IQs of breastfed and bottle-fed children would stay the same over time, but not increase.
If the IQ differences started mainly in later childhood or the gap increased, it would suggest that other factors – such as the children's education – were more important than breastfeeding.
Breastfeeding is more common among better-off families, so breastfed children might have gone to better schools and had access to private tuition.
Additional factors taken into account in the model were the parents' educational achievement and type of employment, the mothers' ages when the children were born, and the children's gestational age (how many months after conception they were born).
The researchers found a small but statistically significant difference in the IQs of girls who had been breastfed and girls who had not at the age of two.
However, the link was quite weak. There was no difference in IQ between boys who had or had not been breastfed.
After that initial stage, there was no statistically significant difference in average IQ between children who had or had not been breastfed once other factors had been taken into account.
Of the children in the study, 62% were breastfed for an average of four months.
The researchers were cautious about the small increase in IQ they found in breastfed girls at the age of two.
"Because our observed effects were weak and at best modest, we interpret the findings as evidence for the lack of benefits of breastfeeding on cognitive development," they said.
In a press statement, they added: "Comparatively small events like breastfeeding are very unlikely to be at the core of something as big and complex as children's differences in IQ."
They said that children's family background and schooling were more likely to explain any differences.
This study suggests that if breastfeeding has any effect on children's intelligence, the effect is small and does not last beyond early childhood. While the study does not rule out any effect, it seems likely that other factors, such as family background, are much more important.
This study has a number of strengths, including the fact that a lot of children (11,582) from a range of backgrounds, representative of the UK population as a whole, were used.
The children were tested nine times during their childhood, using a range of tests previously shown to be a good way of assessing IQ. The researchers constructed their model in a way that took into account factors such as family background before they looked for the effect of breastfeeding.
However, there were a couple of limitations, although the results of this large, well-conducted study appear to be robust and reliable. The number of additional factors included that might have affected children's IQs was relatively small. We don't know anything, for example, about the children's diet after weaning, or their education.
Although they have previously been judged as reliable, the tests used to measure IQ were carried out by the children at home, supervised by the parents. Some early tests relied on the parent's observations about the child, rather than an objective test of ability.
It's possible that these tests were less reliable than if they'd been given by a trained, impartial researcher. All the children involved in the study were twins, so the results may not be directly applicable to single births.
However, breastfeeding has many beneficial effects on children's health, including the development of a healthy immune system. Public Health England recommends that babies should only be fed breast milk for the first six months of life, where possible.
Other ways you can help your child's cognitive development include reading to them and involving them in creative play, such as drawing or playing pretend games. Read more about play ideas and reading with your child.