Positive association between breastfeeding and intelligence, between three tiers of family income. Five IQ points is 1/3 of a standard deviation.
Editor’s note: I would like to tread very lightly on this topic because of the complexity of the relationships between all the factors discussed and the implications a study like this has. I probably would not have written about it at all, had it not been published in such a prestigious medical journal, and had been as comprehensive as it was.
Breast milk is the ultimate pre- and probiotic. It is essential in developing infants’ microbiomes by inoculating and enriching their guts in certain bacterial species. There have been a number of studies showing alterations of the gut microbiomes of infants that are formula fed, and other studies showing that formula feeding results in a higher risk of asthma and allergies later in life. The complicated relationship between breastfeeding, the microbiome, and phenotypes like autoimmune diseases are not understood at a mechanistic level. Still though, it appears that formula feeding, rather than breastfeeding, may have long term consequences for the health of a child.
To that end, there had been a few small scale studies that demonstrated a general association between breastfeeding an IQ. Just last week, a new study, much more comprehensive than any previous one, delved into this topic and found the same result: duration of breastfeeding was positively associated with IQ, educational level, and income. The results of this study were published in The Lancet.
In 1982 researchers from Brazil began a longitudinal study using a cohort of over 500 newborn infants. At that time, one of the things the scientists measured was the duration that each infant was breastfed. Then, in 2012, the researchers followed up with 3000 of those people in the original study and surveyed them for their educational levels and incomes, as well as measured their IQs. They discovered that each of these three variables was directly related with the length of breastfeeding, with the possibility that over 12 months of breastfeeding actually slightly decreased each. Even after factoring in confounding variables such as maternal education, family income, and birthweight the relationship between breastfeeding and IQ, education, and income still held. The researchers acknowledged the link was tenuous, and that there exists a whole host of other important variables that were not measured in 1982. Nevertheless, the study suggests that breastfeeding improves intelligence upon adulthood.
Breastfeeding, if possible, is clearly preferred to formula feeding, and studies like this show that it may be in everyone’s interest to promote breastfeeding children. It will be necessary to decipher the connection between breastfeeding, the microbiome, and these observations, but with more studies in the pipeline showing the value in breastfeeding everyone should be aware of its importance.