Breastfed babies ‘are more intelligent’

“Breast-fed babies grow into more intelligent children, with IQs up to eight points higher than those who are bottle fed,” the Daily Mail said today. Several newspapers reported on a study that is reputedly the biggest of its kind, looking at 14,000 children for more than six years, which found that breastfeeding improves children’s IQ and academic performance.

The Guardian reported that this study has the added strength that the women in it were randomly allocated to either having breastfeeding support and education aimed at prolonging the duration of breastfeeding, or to receiving standard postnatal care only. It said that earlier studies had suffered from the problem that the women involved had chosen whether they received breastfeeding education or not, meaning that the differences could have been caused by the intelligence or behaviour of the mother. The lead researcher said, “Our study provides the strongest evidence to date that prolonged and exclusive breastfeeding makes kids smarter.”

The study does have some limitations that need to be considered when interpreting its results. However, it is a large and carefully designed study and along with the many other established benefits of breastfeeding, promotes the idea that breast is best.

Where did the story come from?

Dr Michael S. Kramer and colleagues from McGill University in Canada and National Research and Applied Medicine Mother and Child Centre in Belarus, carried out the research. The study was funded by the Canadian Institutes of Health Research. The study was published in the peer-reviewed medical journal: Archives of General Psychiatry.

What kind of scientific study was this?

In this cluster randomised controlled trial, maternity hospitals in Belarus were randomly allocated for their mothers to either receive breastfeeding education or normal maternity care. This was to see whether prolonged and exclusive breastfeeding influences a child’s intelligence by the time they reach the age of six and a half years.

The Promotion of Breastfeeding Intervention Trial (Probit) enrolled 31 Belorussian maternity hospitals between June 1996 and December 1997. In the hospitals and clinics that were randomly allocated to promote breastfeeding, mothers who had chosen to breastfeed received support and education on breastfeeding. Those mothers in the hospitals that had been allocated to the control group received standard care only.

A total of 17,046 babies were involved, all of whom were above standard birth weight. Both groups were similar in areas such as the mothers’ age, education, and whether they smoked during pregnancy, other children living in the house, the number of babies delivered by caesarean and other details of the baby’s birth. The research article does not provide information on the proportion of mothers in the breastfeeding promotion or control hospitals who chose to breastfeed their children, although over 95% of women in Belarus were reported to have chosen to breastfeed in the period of recruitment for the study.

The researchers followed up the children between December 2002 and April 2005, when they were approximately six and a half years of age. This resulted in 13,889 children available for follow up, with 7,108 children in the breastfeeding promotion group and 6,781 in the control group. The follow up included paediatrician interviews, examinations and the children taking the Wechsler Abbreviated Scales of Intelligence (WASI) test: a 30 minute test of vocabulary, maths and geometry. Those children who were at school by this time were also evaluated for reading, writing, maths and other subjects by their teachers. Each child was rated on a scale using the Teacher Report Form of the Child Behaviour Checklist and the teachers did not know what group the children were in when they rated the children.

The researchers used statistical tests to look for differences between children from the breastfeeding promotion and control group.

What were the results of the study?

The breastfeeding promotion prolonged the duration and exclusivity of breastfeeding (breast milk alone). More mothers in this group were still breastfeeding three months after birth (72.7% v 60% in the control group), at six months (49.8% v 36.1% in the control group), at nine months (36.1% v 24.4% in the control group) and at 12 months (19.7% v 11.4% in the control group). The proportion of women exclusively breastfeeding at three months also was much higher amongst the women who had received support (43.3% v 6.4%).

The researchers followed 81.5% of the babies through to childhood (13,889) with no differences in drop out between the two conditions. On the WASI tests they found that children from the breastfeeding promotion group scored significantly higher than the controls on scores of vocabulary (mean 4.9 points higher), similarities (mean 4.6 points higher) and verbal IQ (mean 7.5 points higher) aspects of the test. Other aspects of IQ showed a trend for improved scores in the breastfeeding promotion group, but the differences did not reach statistical significance.

There were no significant differences between the groups in teacher ratings of academic performance (about 75% of the children received school assessment). There were wide within-group differences in scores obtained from the children of each of the different hospitals or clinics in either group.

What interpretations did the researchers draw from these results?

The researchers say that their results are “based on the largest randomised trial ever conducted in the area of human lactation,” and that they “strongly suggest that prolonged and exclusive breastfeeding improves cognitive development as measured by IQ and teachers’ academic ratings at [the age of] 6.5 years”.

What does the NHS Knowledge Service make of this study?

This is a large and carefully designed study. However, there are some limitations worth considering when interpreting it:

• This was primarily a study seeing if a breastfeeding programme aimed at promoting the duration and exclusivity of breastfeeding has an effect on childhood intelligence; not whether breastfeeding in itself has an effect on child intelligence. The researchers could not actually tell women to breastfeed or not as this would be unethical. In both groups, there were women who were breastfeeding, and the decision to initiate breastfeeding was the mother’s personal choice.
• It is not possible to comment on the effect that the four to seven points difference in certain measures of the WASI scale would actually have in terms of intelligence or the academic performance of a child.
• It was not possible to blind the paediatricians conducting the WASI tests as to whether the child had come from the group with breastfeeding promotion or from the standard care group. Some of the paediatricians had themselves been involved in promoting breastfeeding in the postnatal period. Therefore, there is the potential that children from this group were scored more favourably as the paediatricians could have been expecting their scores to be higher.
• Different paediatricians conducted the tests at each of the hospitals and clinics and there was considerable variation in the score results within both groups. To test the validity of these scores, the researchers selected a small group of children (190) for audit tests by independent blinded paediatricians. Although the trend for results was the same (breastfeeding promotion group scores being slightly higher) the size of the point difference was slightly less for each individual measure. A larger sample size for audit would have been ideal.
• The children were only followed for six and a half years. It would be helpful to see whether the breastfeeding support programme had longer-term implications by following the children to a later age.
• A very high proportion of women in Belarus choose to breastfeed their children (reportedly greater than 95% during the period studied), and the duration of breastfeeding appears to be longer than might be found in other countries. Both the breastfeeding support programme and standard postnatal and maternity care may also be different in Belarus than in other countries. This should be considered when trying to generalise these findings elsewhere.
• From this study, it isn’t possible to determine whether any potential benefits to intellect from breastfeeding are actually caused by what is in the breast milk or whether it is the close mother-infant interaction that produces the result (i.e. whether the same effect would be seen if a baby were bottle-fed their mother’s breast milk).

However, regardless of any limitations that this study has, the benefits of breastfeeding are clearly established and this study serves to again promote the idea that that breast is best.

Sir Muir Gray adds...

There are many possible causes of bias in a study like this. Perhaps the mothers who chose breastfeeding were different from the mothers who did not.