Pregnancy and child

Breastfeeding 'doesn't boost children's intelligence'

"Scientists found tots given the boob had the same IQ at age three and five compared to bottle-fed youngsters," The Sun reports in its own unique way.

A new study followed about 8,000 babies in Ireland for five years to look at whether breastfeeding had an impact on problem solving and vocabulary (cognitive abilities), and problem behaviours.

One problem with assessing the effects of breastfeeding is that, in Western countries, mothers who breastfeed tend to have higher levels of education, be middle or upper class, and are less likely to smoke or live in households where there is smoking (as was the case with this study). These factors can skew the overall picture.

So the authors of this study used an approach known as propensity score matching. This involves using complex statistical methods to try and "match" breastfed children with non-breastfed children who have similar combinations of these factors. It aims to reduce the potential impact of these factors in the overall analysis, so they could just focus on breastfeeding. 

Once they did this the only difference they found was that those babies who were breastfed fully for over six months had slightly lower levels of hyperactivity at age three, but not at age five. There was no difference in the breastfed and not-breastfed children's cognitive abilities at three or five.

This study should not discourage women from breastfeeding. The authors themselves note that it does not bring into question the other known benefits of breastfeeding, such as reduced infection rates in babies. However, it may also offer some reassurance to mothers who have not been able to breastfeed.

Where did the story come from?

The study was carried out by researchers from University College Dublin in Ireland and the University of Montreal in Canada. It was funded by the European Union's Seventh Framework Programme, and the lead author was supported by Marie Curie International.

The study was published in the peer-reviewed medical journal Pediatrics on an open-access basis so you can read it online for free.

The reporting of this study is reasonable, although The Sun could perhaps consider a less childish way of describing breastfeeding than being "given the boob". The Mail Online also uses an odd turn of phrase, suggesting that women are under pressure to "resort to" breastfeeding.

What kind of research was this?

This was a cohort study called "Growing Up in Ireland". It followed a group of babies in Ireland from birth to five years of age. The current analysis was looking at whether having been breastfed affected children's cognitive abilities and other development at ages three and five.

While breastfeeding is known to protect babies from infection early in life, its long-term impact on outcomes such as intelligence is less clear. Some studies have found an effect, while others have not.

This type of study is the best way to look at links between breastfeeding and children's outcomes. This is because it would not be feasible to randomly allocate mothers to breastfeed or not. The difficulty with cohort studies is that many confounding factors can influence outcomes. So separating out the influence of individual factors is very difficult.

Women who breastfeed may differ from women who do not in factors such as parental education and socioeconomic status. And some researchers think these factors could be contributing to differences seen in children's cognitive abilities. The current study used a relatively new statistical method (propensity score matching) to try to remove the influence of these other factors in the analyses, so the researchers could isolate the impact of breastfeeding alone.

What did the research involve?

The researchers randomly selected families with babies born in a six-month period between the end of 2007 and early 2008 in Ireland to be invited to participate in the study.

They enrolled over 11,000 babies, and collected information about them from birth up to the age of five.

The current study looked at whether those babies who were breastfed differed in their outcomes at ages three and five from those who were not breastfed.

The researchers only analysed data from children who were born at term (that is, were not premature) and whose families had provided all required information when they were aged nine months. About 8,000 babies had complete information at this age and were successfully followed up to age five.

At nine months the mothers were asked four questions about breastfeeding, and the babies were grouped into those who had been breastfed at some point, and those who had never been breastfed.

Those in the first group were grouped according to how long they were breastfed for:

  • up to 31 days
  • between 32 and 180 days
  • 181 days or longer

The researchers tested the children's problem-solving skills and vocabulary (cognitive abilities) at ages three and five years. They also measured any problem behaviours.

The researchers then used a technique called "propensity score matching" to match the breastfed and not-breastfed groups for 14 confounding factors other than breastfeeding that could affect results, such as:

  • baby gender, birthweight and delivery method
  • maternal age, education, working status and presence of depression
  • presence of mother’s partner in the home
  • family social class, receipt of free medical care or not, and smoking in the household during pregnancy
  • presence of brothers and sisters in the household

They looked at whether, once they had done this, there were any differences in cognitive abilities or problem behaviours at ages three and five years.

What were the basic results?

The researchers found that about 60% of babies were at least partially breastfed for up to a month. Just over 40% were at least partially breastfed for between one and six months, with only about 5% continuing for over six months.

There were differences between the family circumstances of the breastfed and never-breastfed babies. The breastfed babies' families were, for example:

  • more likely to include the mother's partner in the household
  • more likely to be of higher social class (professional/managerial)
  • less likely to be receiving free medical care
  • more likely to have a higher maternal education level
  • more likely to have the mother in work
  • less likely to have a young mother (age 24 or under)
  • less likely to have been smoking during the pregnancy

The researchers carried out their statistical "matching" of the groups to remove the impact of these factors. They found no significant differences between the babies breastfed for up to six months and non-breastfed babies at ages three or five in cognitive abilities or problem behaviours.

Those babies who were fully (exclusively or almost exclusively) breastfed for over six months had slightly lower hyperactivity levels at age three (as rated by parents) than those who were never breastfed. This difference was not seen in those who were partially breastfed for this long, or by the time the children reached age five. 

How did the researchers interpret the results?

The researchers concluded that when looking at cognitive abilities and problem behaviours at ages three and five, breastfeeding was only associated with a small benefit in hyperactivity at age three.

There were no significant benefits seen in these outcomes at age five, once the children were at school. Importantly they note that "these findings do not contradict the many [other] medical benefits afforded to both mother and child as a result of breastfeeding".


This study has tackled the controversial question of whether there are long-term benefits of breastfeeding for cognitive ability or problem behaviours when children are older (ages three to five).

Although they found very limited evidence of benefit, the authors do note that there are some other studies that have used a similar analysis but found differing results. The researchers think this could be due to slight differences in analysis.

This does highlight the difficulties in being absolutely certain whether breastfeeding has direct impact on long-term cognitive outcomes.

What we can say is that, if there are differences, they do not appear to be large once other factors are taken into. This may be reassuring to women who were not able to breastfeed.

The strengths of this study include its large size, the fact that it followed participants prospectively for a long period, and took into account a large number of factors that could be influencing the link. There are some limitations. For example, they collected information on breastfeeding at nine months. In some cases mothers may not have been able to accurately remember exactly how long they breastfed for by that point, or felt pressure to report longer durations than were actually achieved.

This does not mean that it is not worth breastfeeding if you can. This study did not look at all aspects of baby and child health and wellbeing. Breastfeeding is known to protect babies against infections. It also helps reduce their risk of obesitytype 2 diabetes and cardiovascular disease in adulthood. Breastfeeding also offers health benefits for the mother – reducing risk of breast and ovarian cancer, as well as osteoporosis and cardiovascular disease.

Some women find it difficult to breastfeed, and it's important to ask for help early.

Read more about common breastfeeding problems and what can be done about them.

NHS Attribution