Professor Horta, what are the short term benefits of breastfeeding?
Breastfeeding protects against infectious diseases, morbidity and mortality from pneumonia and diarrhoea in childhood is lower among breastfed children. In a systematic review and meta-analysis carried out in 2013, we observed that hospitalization and mortality from diarrhea were 72% and 77% lower among breastfed infants, respectively. Concerning respiratory infection, the risk of hospitalization was 57% lower among breastfed infants, whereas mortality was 70% lower.
How long back did you and your team set out to establish the relationship between breastfeeding to IQ and achievement?
Our first study on the association between breastfeeding and school achievement was published in 2005. We observed that breastfeeding duration was positively associated with achieved schooling among males at 18 years of age.
What was the sample size of those enrolled for the study?
In 1982, we daily visited the maternity hospitals in Pelotas and identified all hospital deliveries. Those live births whose family lived in the urban area of the city were examined and their mothers interviewed (n=5914). And these subjects have been followed for several times through the life cycle. From June 2012 to February 2013, we tried to follow the whole the cohort and 3701 study participants were interviewed, which represented a follow-up rate of 68.1%.
Were you able to clearly establish the relationship with IQ and what was the enhancement in the IQ and by what age was it evident?
The causal nature of the association between breastfeeding and intelligence has been challenged because of the possibility of residual confounding by socioeconomic status, parental intelligence or genetic factors, including the possibility that infants who are better developed or more mature may breastfeed for longer periods. With respect to residual confounding by socioeconomic status, in our setting breastfeeding is independent of socioeconomic status. Therefore, the observed association between breastfeeding and intelligence in early adulthood is not due to residual confounding by socioeconomic status. With respect to parental intelligence, we adjusted the estimates to parental schooling, a proxy of intelligence. Concerning residual genetic confounding, in another analysis, we further adjusted the estimates to a schooling allele score and the estimates slightly changed. Suggesting, therefore, that residual genetic confounding is an unlikely explanation for the association between breastfeeding and intelligence. Therefore, we have strong evidence on the existence of an association of breastfeeding with intelligence. In our study, intelligence was only assessed at 30 years. But, in a previously published meta-analysis, we observed that this association has already been reported in early childhood.
Similarly what did your studies show about the relationship of breastfeeding to the level of income or attainment?
We observed that breastfeeding is also positively associated with income and school achievement at 30 years. Schooling was 0.91 years higher among those who had been breastfed for at least 12 months in relation to those who breastfed for less than one month. Monthly income was 341 Brazilian reais (equivalent to a third of the average income) higher among those who breastfed for at least 12 months. These differences were observed even after controlling for confounding variables.
Does the social pattern of breastfeeding differ between high income and low income countries?
In most of the high-income countries, duration of breastfeeding is positively associated with socioeconomic status, whereas most of the studies carried out in low and middle income countries have reported that breastfeeding is independent of socioeconomic status.
Does also the level of income within a society or country have a difference in the pattern of breastfeeding?
I answered this question in my previous answer.
What are the consequences?
As previously mentioned, in our setting duration of breastfeeding is independent of socioeconomic status. Furthermore, the association between human capital and breastfeeding was also observed after controlling for the schooling allele score. Therefore, it is unlikely that this association is due to residual genetic confounding, and we strongly believe that breastfeeding is positively associated with performance in intelligence tests.
Our readers are mainly the youth from many part of the world who look up to achievers such as yourself. A word of advice for them and the would be parents?
Breastfeeding has clear benefits for the child, on the short and long-term. Breastfeeding is an investment in the future of the child.
Photo: From the archive of Professor Horta