So does breastfeeding affect
intelligence or not?

Breastfeeding and intelligence

A study published in early October 2006 published results that breastfeeding does not affect a child's intelligence.

"In the largest study ever to address the issue, researchers found a positive impact for breastfeeding on intelligence only when other potential contributors -- such as the mother's IQ and the parents' educational and economic status -- were not taken into consideration."
Breastfed Babies Aren't Smarter

How could that be? many wonder, because in the past there have been several other scientific studies that have shown a positive effect of breastfeeding on intelligence.

Just stop and think: does ONE new study suddenly nullify all other previous results?

The way media outlets report on scientific studies, you would almost think so.

But that is almost never the case. We should never believe blindly any one study's results, especially if it the news reports sound sensational.

A new study can add to our knowledge, but if it contradicts previous results, that does not mean the earlier studies were in the wrong. It means that scientists and researchers need to find out WHY there is a discrepancy. Usually there IS an explanation for conflicting results.

Possible explanations

1) How is breastfeeding defined?

This study was using data from 1979 US national longitudinal survey of youth. In that, women had been asked whether they breast fed the child at all, and, if so, how old the child was when they stopped breast feeding.

In other words, the children classified as "breastfed" in the study could have been receiving 70% of their nutrition from formula, and 30% from breast milk. Or 90% and 10%. Or 0% and 100%. The children were classified as "breastfed" if they were breastfed at all, and formula-fed if otherwise.

Drawing conclusions about the effect of breastfeeding based on such a distinction is like drawing conclusions about the effect of not smoking in a population where some people claimed to have smoked continuously, while others said they smoked partially, occasionally, or intensively for short periods.

Or, one would not expect that research looking at the impact of eating vegetables on health would be useful if it was comparing a group of non-vegetable eaters who ate at McDonalds every day and a group of vegetable eaters who ate McDonalds 6 days a week and vegetables on one day would be useful. Similarly, you cannot expect that token breastfeeding can wipe out the impact of predominant formula feeding.

The crucial question that was not asked in that 1979 survey was, "Was the child exclusively breastfed, and if yes, for how long?"

The exclusively breastfed babies are THE true control group when trying to access effects of breastfeeding. (Unfortunately, when using United States data, those kind of babies are not very numerous so that makes conducting studies harder.) Studies should compare babies exclusively breastfed for first 6 months of life to totally formula-fed babies. The large group of mixed-feeders just confounds everything.

2) Another possible variable to take into account is the breastfeeding mother's diet.

We know that the fatty acid DHA affects babies' intelligence; that is why it is now added to many formulas.

Another fact well proven is that breast milk levels of DHA vary according to how much DHA mom gets. Eating fish (or taking fish oils) makes the levels go up.

In fact, a recent report Seafood Choices: Balancing Benefits and Risks by Institute of Medicine found evidence that maternal consumption of omega-3 fatty acids through seafood can contribute to vision and cognitive development in infants and lengthen the duration of gestation.

Typically, US mothers' don't eat much fish and their milk's DHA levels are low. But even a governmental agency is now basically recommending that mothers eat certain types of fish (avoiding the large predator fish that have the highest levels of mercury) to get adequate amounts of DHA fatty acids because it helps visual and cognitive development of their babies.

So there's an idea for yet a different study: how does mother's fish consumption affect her breastfed baby's intelligence?
(DHA is not the only factor in breast milk that helps the brain develop; for example the high lactose content is another.)

Newer results

A study published in 2007 found a VERY interesting relationship between breastfeeding and intelligence: it showed that whether breastfeeding affects a child's intelligence depends on a certain gene. In 90% of the children, the gene is such a way that breastfeeding DOES affect the child's intelligence, probably by affecting the fatty acid metabolism, or the way the body processes fatty acids. In the remaining 10%, breastfeeding versus bottle-feeding has no effect on intelligence.

This important finding now sheds some light on the previous studies that have had mixed results: there is another counfounding factor there, in the children's genetic material. But it further confirms the intellectual advantage breastfeeding can give for 90% of the children. (And of course even the 10% are helped by breast milk in other ways.)

Then, a study published in 2008 studied nearly 14,000 children in Belarus, and found that at age 6, the breastfed group scored almost 6 points higher on an IQ test. This is an improtant result because it is a large group, a randomized controlled trial, and the study design was such that the researchers were able to see the effects of breastfeeding alone without the confusing variables of maternal socioeconomic status and intelligence.

Sources

'Effect of breast feeding on intelligence in children: prospective study, sibling pairs analysis, and meta-analysis' by Der, Batty and Deary

The association between duration of breastfeeding and adult intelligence.
by Erik Lykke Mortensen, Kim Fleischer Michaelsen, Stephanie A. Sanders, and June Machover Reinisch, JAMA 287: 2365-2371
and
Breast-Feeding Linked to IQ Gain
By Marc Kaufman Washington Post May 8, 2002
This study examined young men and women from Copenhagen, Denmark. I just wonder how much more fish the Danish eat as compared to U.S. women.

Moderation of breastfeeding effects on the IQ by genetic variation in fatty acid metabolism
Proc. Natl. Acad. Sci. USA, published November 5, 2007, 10.1073/pnas.0704292104.
See also a news article Gene links breastfeeding to IQ.

Breastfeeding Boosts Mental Health, New Research Reveals
A new study has found that babies that are breastfed for longer than six months have significantly better mental health in childhood.

Study: Breastfeeding pushes kids up a social ladder
Researchers say one possible reason for the findings could be that breastfeeding improves health, stature and IQ.
Breastfeeding in infancy and social mobility: 60 year follow-up of the Boyd Orr cohort Arch. Dis. Child., Feb 2007

Breastfeeding and child cognitive development: new evidence from a large randomized trial.
by Kramer et al. This is the study done in Belarus. Arch Gen Psychiatry. 2008 May;65(5):578-84.

Breastfeeding builds brighter brains

Breastfeeding and intelligence from InFact Canada - referencing four scientific studies on the matter.

By sending in your comments, you agree that 007 Breasts may publish and edit your comments, or choose not to publish them for any reason.

Small breasts
Large breasts
Nipple worries
Breast development
Some other question? Check our Q & A page!