How much was previously known about breastfeeding duration and intelligence?
Several studies have previously reported a benefit of breastfeeding on performance and intelligence tests in children and adolescents, but, in adults, these benefits have not really been assessed.
Furthermore, studies have reported an increased performance in IQ tests among children who had been allocated either to receive breast milk during their stay at the inter-city care unit or among children whose mothers had been allocated to receive a Breastfeeding Promotion Intervention.
Finally, in a systematic review and meta-analysis that we carried out, which should be publish in the next couple of months, we observed a minimal effect of about a 2.5 points difference in IQ performance between adolescents and children who were breastfed and those who were not.
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In what way did your recent research impact this understanding?
Our research shows a benefit of breastfeeding on performance in IQ tests that was similar to the benefit reported in previous tests among children and adolescents, suggesting that the benefits of breastfeeding are still observed in adulthood.
Our first question was: is the benefit that we're observing in adolescents and children still observed in adulthood? We are showing that it is.
The other question was that if breastfeeding leads to an approximate 3.0 point rise in IQ, what is the meaning of this difference and what are the consequences?
We show that this small difference in IQ has a real effect later in life, by increasing school performance and achievement, as well as income during adulthood.
What did your recent study involve and how did you measure intelligence?
We have been following these subjects since their birth. During the last visit, when the subjects were aged 30 years, we carried out examinations using a psychological interview and the Wechsler Adult Intelligence Scale.
How many people did you study?
We were able to follow about 3,700 subjects at 30 years.
What are the main factors you considered when choosing an intelligence test to use and in what ways are IQ tests limited?
Well, of course, one factor was using an IQ test that could give results that were comparable with other studies. We decided to use the Wechsler Scale because it is the most commonly used among other studies.
The problem or the limitation of IQ tests is that they do not provide a full picture of someone’s intelligence and show only some dimensions. These tests assess only a part of the human overall competence because we have emotional intelligence and other domains of intelligence that cannot be assessed by IQ tests. This means you only determine school-related success and not life success in general.
How did you disentangle the effect of breastfeeding from that of socioeconomic advantage?
First of all, in contrast to what has been observed in most high-income countries, in Pelotas, the prevalence of breastfeeding is not affected by socioeconomic status. The poor mother and the wealthy mother breastfeed for more or less the same amount of time. Therefore, socioeconomic status should not be considered as a real confounder in our studies.
However, we still decided to adjust our estimates for several socioeconomic variables. We included in the analysis several different measures of socioeconomic status to show that our results are not confounded by socioeconomic status.
Which factors did you take into account?
We included maternal schooling, maternal income, federal income, and house score index, which measures not only the possession of goods, but also the type of house construction.
What were your main findings and were you surprised by these results?
Our main findings were that breastfeeding is positively associated with IQ, income and schooling. What surprised us was the magnitude of the association between breastfeeding and income. I did not expect the benefit to be so huge, but it was a positive surprise.
What do you think is the likely mechanism underlying the beneficial effects of breast milk on intelligence?
That is a good question. It could be a nutritional effect because breast milk carries some nutrients such as body saturated fatty acids that were not present in the formulas available when our subjects were babies. Those fatty acids are related to brain development, so that is one explanation.
Another explanation could be that breast milk promotes bonding between the mother and child, which is also thought to boost the child’s development.
What are the public health implications of your research?
Well, this is very important. Irrespective of whether there is a nutritional or psychological, maternal bonding effect, our findings have reinforced the importance of promoting breastfeeding.
The societies and government should take action in terms of promoting breastfeeding and those actions should be tailored for every country, according to the factors related to a shorter duration of breastfeeding in each place.
What further research is needed to corroborate your findings?
The findings should be replicated in another setting because one important factor to consider when assessing relative associations, is whether or not our findings in one setting are replicated in others.
Where can readers find more information?
Association between breastfeeding and intelligence, educational attainment, and income at 30 years of age: a prospective birth cohort study from Brazil. Victora, Cesar G et al. The Lancet Global Health , Volume 3 , Issue 4 , e199 - e205 http://www.thelancet.com/journals/langlo/article/PIIS2214-109X%2815%2970002-1/abstract
About Dr Bernardo Lessa Horta
PhD in Epidemiology and Biostatistics – McGill University. Associate Professor Postgraduate Program in Epidemiology – Universidade Federal de Pelotas
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