Children who were breast-fed for more than 4 months were more likely to gain good grades in their examinations at age 16 compared with non-breast-fed children, according to a new study from the National Perinatal Epidemiology Unit at the Nuffield Department of Population Health in the University of Oxford.
Researchers noted that existing evidence suggested that breast-feeding duration was associated with improved cognitive development, but studies were not consistent as to whether the gains persisted after results were adjusted to account for important confounders, such as socioeconomic position and maternal intelligence.
Links with Cognitive and Educational Outcomes 'Debated'
"Consequently, the importance of breast-feeding for improving cognitive outcomes continues to be debated." Furthermore, "educational attainment is related to cognitive ability, and is a strong predictor of life trajectories", they said. However empirical evidence that breast-fed children have better school results than non- breastfed children remained "inconsistent".
Researchers analysed data on 4940 children born from 2000 to 2002 and enrolled in the Millennium Cohort Study, which followed up the children at ages 3, 5, 7, 11, 14, 17, and 22. They linked self-reported breast-feeding data from the study to the National Pupil Dataset, which stores longitudinal academic data of students enrolled in English state schools.
1 in 3 Infants Never Breast-fed
In the whole cohort, one third of the infants (32.8%) were never breast-fed, while almost 1 in 10 (9.5%) had been breast-fed for 12 months or longer. Children who were breast-fed for longer were more likely to have older mothers of higher social class and with higher educational qualifications.
In the crude analysis, all breastfed infants were more likely to achieve the crucial school outcome of five GCSEs with marks of 5 or greater than those who had never been breast-fed. Children who had been breast-fed for at least 4 months were 1.6 times more likely to achieve this outcome than those never breast-fed. Adjustment attenuated the effect, but the association with feeding durations of 4 months or longer persisted (RR: 1.13; 95% CI 1.02 to 1.23).
Longer Breast-feeding Linked with Higher GCSE Passes
Compared with children who were never breast-fed, those who were breast-fed for longer were more likely to have a high pass in their English and mathematics General Certificate of Secondary Education (GCSE), and were less likely to fail the English GCSE, but not the mathematics GCSE.
Only around a fifth (19.2%) of children who were breast-fed for at least 12 months failed their English GCSE, compared with 41.7% of those who were never breast-fed, while 28.5% of those breast-fed for at least 12 months achieved a high pass (A and A*) compared with 9.6% among non-breast-fed children.
For the mathematics GCSE, only 23.7% of children who were breast-fed for at least 12 months failed their test compared with 41.9% of those never breast-fed, while 31.4% of those breastfed for at least 12 months achieved a high pass (A and A*) compared with 11% among non-breast-fed children.
Additionally, compared with those never breast-fed, those breast-fed for at least 4 months had, on average, a 2-3 point higher attainment 8 score (a measure of scores across eight government approved school subjects ).
Gains 'Modest' but Persisted After Adjustment
The study, published online in Archives of Disease in Childhood, concluded that "longer breast-feeding was associated with modest gains in academic outcomes" and this was true "even after full adjustment for socioeconomic markers and maternal cognitive ability".
The strength of the association equated to a 38-39% increase in the probability of achieving high marks in both GCSEs, and a 25% reduction in the probability of failing English, the researchers said.
The team said their findings were nationally representative for children enrolled in state schools in England, and the large sample size allowed them to detect outcome differences between several breast-feeding duration groups.
They concluded: "Breast-feeding duration was associated with improved educational outcomes at age 16 among children living in England, after controlling for important confounders.
"However, the effect sizes were modest and may be susceptible to residual confounding." They suggested that future studies should adjust for both socioeconomic circumstances (comprehensively) and maternal general intelligence.
"Breast-feeding should continue to be encouraged, when possible," they urged, "as potential improvements in academic achievement constitute only one of its potential benefits."
Commenting on the study to the Science Media Centre, Andrew Whitelaw, emeritus professor of neonatal medicine at the University of Bristol, said: "It has been shown repeatedly that, in developed countries, breast-fed infants have significantly better scores on a variety of developmental tests and educational outcomes.
"This finding is confounded by mothers who breast-feed having consistently better education and socio-economic status, both factors that are associated with improved educational outcomes in their children. It is an important question as to whether this is a biological effect of substances in breast milk or whether intelligent mothers tend to have smarter children anyway by a combination of good genes and stimulating home environment."
He noted: “A true biological effect of substances in breast milk might be expected to show a 'dose effect', and another strength of the study is that the investigators were able to examine different durations of breast-feeding from zero to over 12 months." In fact the authors found that there was a dose effect, and this combined with statistical techniques to eliminate confounding factors such as maternal intelligence and socio-economic status "is the nearest an observational study can get to proving cause and effect".
"Thus, they went a little further than previous studies in identifying a pure biological effect of breast milk on child development," Prof Whitelaw said. He concurred with the authors that: "This is one of many important benefits of breast-feeding on the child and the mother."
The study was funded by the Nuffield Department of Population Health at University of Oxford. The authors declared no conflicts of interest.