IQ and breastfeeding

A recent Brazilian study has found that longer-breastfeeding was linked to higher IQ. The study, published in the prestigious peer-reviewed journal the Lancet, began with 5,914 newborn babies in 1982, and were able to follow up with 3.493 of those individuals three decades later.

The study found that those babies who had been breastfed for up to a year, as opposed to those who has been breastfeed for one month or less, score up to 4 IQ points on average when tested by the age of 30.  The study also found that, perhaps as a consequence of developing higher IQs, the follow-up cohort had 0.9 years of additional schooling and that the earnings were higher by a third of the average income. The authors took the care of controlling for a number of confounding variables such as maternal education, birth weight of the child and smoking during pregnancy.

According to this study, IQ and breastfeeding are positively correlated, which gives credence to the UK Government’s stance that “breast is best”.

Although some have considered that the follow-up rate of 59% is relatively weak, (as a rule of thumb, a drop-out rate of 20% or more is considered to be reasonably high)  there is no suggestion that the individuals who were traceable during the follow-up would represent a group with directionally predictable IQ behaviors. The fear is of course that people who were traceable would have had higher IQ, although it is equally safe to assume that individuals with the highest IQs would be the most mobile, and could therefore have been more difficult to trace in the follow up period. With a final sample of c.3,500, is it reasonably safe to assume that the results of the study ought not to be compromised owing to the survivorship rate of the original sample of babies.

Another criticism of the study is that mothers were asked to recall breastfeeding habits three decades later, which could have resulted in recollection errors, which could distort the ability to accurately study the link between IQ and breastfeeding. This is perhaps the study’s greatest weakness, although mother’s tend to have a fairly good recollection of details surrounding the birth of a child.

IQ and breastfeeding are positively correlated: although you need the right genes.

In any case, the recent Brazilian study backs several prior research studies that have also found a correlation between IQ and breastfeeding. A 2007 study of UK and New Zealand newborns has also found that IQ and breastfeeding are positively correlated variables. Specifically, the researchers found that babies which had carried the C-genotype of the gene known as FADS2 (90% of people possess the C genotypes, while 10% possess the G genotype), a gene which is closely associated with the processing of fatty acids in diets, recorded average IQs of up to 7 points higher than children who either possessed the G genotype or who were not breastfed. This led to the conclusion that the vast majority of people are genetically predisposed to get an IQ boost from breastfeeding.

So the emerging evidence appears to be that IQ and breastfeeding are positively linked, and if you are a mother who is able to breastfeed your child, then you should do this.  If you are unable to breastfeed, either because it doesn’t work or is too painful or stressful, then there is no point in beating yourself up over the issue as heritability is likely to be a much stronger variable than breastfeeding. But that said, the most important takeaway is that mothers should nurture their babies in the best way that they can.

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