Prolonged Breast-Feeding Linked to Higher Adult IQ

Prolonged Breast-feeding Linked to Higher Adult IQ
Troy Brown, RN
March 18, 2015
Prolonged breast-feeding is associated with higher intelligence in adulthood, longer schooling, and higher adult income, according to a study published March 17 in the Lancet Global Health.
"Our study provides the first evidence that prolonged breastfeeding not only increases intelligence until at least the age of 30 years but also has an impact both at an individual and societal level by improving educational attainment and earning ability," said coauthor Bernardo Lessa Horta, PhD, from the Federal University of Pelotas, Brazil, in a journal news release. "What is unique about this study is the fact that, in the population we studied, breastfeeding was not more common among highly educated, high-income women, but was evenly distributed by social class. Previous studies from developed countries have been criticized for failing to disentangle the effect of breastfeeding from that of socioeconomic advantage, but our work addresses this issue for the first time."
The researchers conducted a prospective, population-based birth cohort study of neonates born in 1982 in Pelotas, Brazil. They recorded information about breast-feeding in early childhood and examined IQ (Wechsler Adult Intelligence Scale, 3rd version), educational attainment, and income when the offspring were approximately aged 30 years.
The investigators used multiple linear regression and adjusted for 10 confounding variables, including parental education, household score index, genomic ancestry, maternal smoking during pregnancy, maternal age, type of delivery, maternal body mass index before pregnancy, gestational age, and birth weight.
Information about IQ and breast-feeding duration was available for 3493 of 5914 neonates originally enrolled in the study.
The researchers found a positive association between durations of total and predominant breast-feeding and IQ, educational attainment, and income, as well as dose–response associations with breast-feeding duration for IQ and educational attainment.
Specifically, adjustment for confounders, those who had been breast-fed for 12 months or longer had higher IQ scores (difference, 3.76 points; 95% confidence interval [CI], 2.20 - 5.33 points), more years of education (difference, 0.91 years; 95% CI, 0.42 - 1.40 years), and higher monthly incomes (difference, 341.0 Brazilian reals; 95% CI, 93.8 - 588.3 reals) compared with those who had been breast-fed for less than 1 month.
Mediation analysis suggested that 72% of the total effect of breast-feeding on income at age 30 years is mediated by an individual's adult IQ.
"The magnitude of the identified effects was important in public health terms," the authors write. "The difference in IQ between the most extreme groups was nearly four points, or about a third of a standard deviation; the increase of 0.9 years in education corresponds to roughly a quarter of a standard deviation, and the difference in income of R$341 was equivalent to about a third of average income."
"The likely mechanism underlying the beneficial effects of breast milk on intelligence is the presence of long-chain saturated fatty acids (DHAs) found in breast milk, which are essential for brain development. Our finding that predominant breastfeeding is positively related to IQ in adulthood also suggests that the amount of milk consumed plays a role," Dr Horta explained in the news release.
In a linked comment, Erik Lykke Mortensen, MSc, from the Department of Public Health and Center for Healthy Aging, University of Copenhagen, Denmark, writes, "With age, the effects of early developmental factors might either be diluted, because of the effects of later environmental factors, or be enhanced, because cognitive ability affects educational attainment and occupational achievements.... Victora and colleagues' study suggests that the effects of breastfeeding on cognitive development persist into adulthood, and this has important public health implications."
Mortensen concludes, "The findings from this Brazilian cohort suggest that breastfeeding might have long-term effects on intelligence in a population without strong social patterning of breastfeeding, and this effect might mediate effects on life outcomes, such as educational attainment and income. However, these findings need to be corroborated by future studies designed to focus on long-term effects and important life outcomes associated with breastfeeding."
The Wellcome Trust, International Development Research Center (Canada), Conselho Nacional de Desenvolvimento Científico e Tecnológico, Fundação de Amparo à Pesquisa do Rio Grande do Sul, and the Brazilian Ministry of Health funded the study. The authors and Mortensen have disclosed no relevant financial relationships.
Lancet Glob Health. Published online March 17, 2015.

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