Breastfeeding duration may be associated with IQ score and level of education

Beyond being essential for growth, breast milk provides many benefits to both baby and mother. Babies who are breastfed have a lower risk for developing:

These health benefits are likely due to the presence of antibodies in the breast milk that confer some protection to the infant from bacteria and viruses. Many of the health benefits of breast milk are still being researched but the general consensus is that breast milk is good for your baby and the longer you can maintain feedings the better the outcomes for your baby will be. The beneficial effects of breastfeeding are not limited to the infant. Mom’s who breastfeed will feel a stronger maternal bond to the infant thanks to the release of hormones into the blood and will also have a decreased risk for developing breast, ovarian, and endometrial cancers. There is also a decreased risk of developing post partum depression in mothers who breastfeed. Breastfeeding is not always possible due to the presence of infectious diseases or certain medications and as such, formulas are often used to replace breast milk for a period of time. They do not offer many of the same benefits but will keep the baby nourished until breast feeding can resume.

For many years people have wondered whether there was a link between breastfeeding and intelligence later in life. The results have been mixed (12) and the answer to this question is still very much up in the air. A recent report, published in The Lancet Global Health hopes to shed some more light on the debate.

The study that was launched in 1982 recorded information about breastfeeding frequency and duration on 3,493 infants in Brazil. When these people reached the age of 30, they collected information about their scores on a standardized IQ test, their educational attainment (in years of education), and their income. Their results showed that the longer the people were breastfed as infants, the more their IQ score and educational level increased. In particular, they found that participants who were breastfed for 12 months or more had their IQ score increase by an average of 3.7 points over participants who were breastfed for less than 1 month. These participants also had almost a year’s more of education and earned about $340 more per month than those who were breastfed for less than a month. The researchers think this increase in income is likely due to the increase in IQ score. An important point of this study is that the researchers controlled for many other variables that could account for differences in IQ and earning potential. These included family income, maternal education, maternal smoking during pregnancy, maternal age, maternal weight before pregnancy and the participant’s birth weight. Each of these factors have been shown to impact IQ scores. Even after correcting for these variables the researchers saw a significant effect of breastfeeding on IQ.

Now for the important question, does this much of an increase really matter that much? Sure it was significant increase, but how much does a change in about 4 IQ points make in intelligence or an extra year of schooling make in education? There is a phenomenon known as the Flynn effect where peoples intelligence has been steadily increasing (measured by IQ tests) since the 1930s. It has been calculated to be around 3 IQ points per decade. Taking this into account, the participants in this study would have had an IQ that increased by 9 points over the duration of the study, so again, how much difference does 4 points make? What about the people who didn’t breastfeed for a whole year but somewhere in between? 6-12 months of breast feeding was associated with a 3.5 IQ point increase. 3-6 months? That was a 1.8 point increase. Any breastfeeding duration over a month was associated with an increase. It is also important to know that many people believe the IQ test is not a perfect measure of intelligence because it neglects creativity and emotional intelligence. Similar to the small IQ increase, 0.9 years extra education may not make much of a difference, or it could make all the difference. That is the difference between a bachelor’s degree and a master’s degree in some disciplines. The results seem small, but we don’t really know the real world importance of them yet.

But does it really matter if the IQ increase really means anything? Does it matter if the increase in education or earning potential is large enough? No, with all the other benefits breastfeeding provides, the IQ and other increases are the least important of all the benefits. This is just another addition to the long list of breast milks benefits. More and more women in western society are returning to breastfeeding and that is a good thing. We need to be more accepting of breastfeeding, especially if it will make our future generation smarter and healthier.

Just remember, correlation does not equal causation and more work still needs to be done before this result is confirmed. 


2 thoughts on “Breastfeeding duration may be associated with IQ score and level of education

  1. Props for promoting breastfeeding.

    I don’t think the Flynn effect affects results exactly. (As I imperfectly understand it, there is a lot of debate about its interpretation too.)

    What I would like to know: did they actually measure and control for parental intelligence? IQ, like almost anything, is partly heritable. If smarter parents breastfeed longer and pass on more intelligence, the study’s showing the reverse of what they imply (IQ=breastfeeding instead of breastfeeding=IQ). But they would have thought of that… right?

    Also, one possible contributor to the Flynn effect is improving nutrition in the last few generations, quite related.


    • You’re right, I do not think the Flynn effect changes the results and is open to quite a bit of debate. I was aiming to put the change in IQ into context. 4 points over 30 years (1.33 points per decade) is less than the expected 3 per decade that most people may see in a population so it may not be a huge difference (although does it really matter with all the other benefits of breastfeeding).

      In response to your question, yes they did control for paternal intelligence to some degree although not by measuring IQ. At birth, they took a measure of the mothers education in years and then at two visits post recruitment they took a measure of parental education in years. They controlled for both of these variables (along with others including socio-economic status) in their analysis and after controlling for them, the results were significant. Whether this means increases in breastfeeding duration lead to greater IQ, still debatable but the study was interesting to say the least. Still need cause an effect before it is confirmed and you wont get that from this type of study.

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