To investigate the extent to which socioeconomic position and maternal cognitive ability explains the association between breastfeeding and cognitive development, researchers from NPEU led a new analysis using data from the UK Millennium Cohort Study (MCS)*. The results have been published today in PLOS ONE.
The dataset included information on 7,855 children born in 2000-2002, who were followed up to age 14 years. For each child, two aspects of cognitive ability were assessed using standard tests. The first of these, verbal ability, describes the ability to understand and communicate effectively with words, and was assessed at 5, 7, 11, and 14 years. The second, spatial ability, tests the ability to mentally visualise and manipulate objects and shapes, and was tested at 5, 7, and 11 years.
Mothers completed survey questions about whether they had breastfed their child and for how long. The analysis also included information on the mothers' socioeconomic position (measured by occupational social class and level of formal education) and their cognitive ability (based on a verbal cognitive test).
Out of the total study sample, 34% of the children had never been breastfed, and 23% had been breastfed for at least six months.
Children who were breastfed for longer were more likely to be growing up in socially advantaged families (for instance, their mother may have had a higher level of formal education).
Longer breastfeeding durations were associated with higher verbal and spatial cognitive scores up to ages 14 and 11, respectively.
Taking into account the mother's socioeconomic position approximately halved the effect of breastfeeding duration on both cognitive abilities.
Taking into account maternal cognitive ability further reduced the influence of breastfeeding, but a modest effect remained.
For verbal ability, the largest effect size was seen at age 14. Compared with children who had never been breastfed, children who had been breastfed for longer than 12 months had a mean score that was 0.26 standard deviations higher.
For spatial ability, the largest effect was seen at age 11, for children who were breastfed for between 4 and 6 months. Compared with children who were never breastfed, this group had a mean score that was 0.25 standard deviations higher.
According to the researchers, the potential mechanisms by which breastfeeding could improve cognitive development include the provision of nutrients important for neural development, such as polyunsaturated fatty acids (PUFAs) and micronutrients (including iron, folate, zinc, and choline). In addition, breastfeeding offers long-term protection against infectious diseases and other illnesses which may affect early development.
However, it remains possible that the association between breastfeeding and cognitive development is caused by other characteristics the researchers could not account for in the study, such as the father's intelligence.
Reneé Pereyra-Elías, a DPhil student in NPEU and lead author for the study, said: 'Our study showed that the positive associations between breastfeeding duration and cognitive development still remain after accounting for social advantage and maternal intelligence. Although the effect we see is small for individual children, it could have a much larger impact when we think about the effect across all children in the population.'
Associate Professor Claire Carson (NPEU), a co-author for the study, added: 'A real strength of this study is that we had detailed data on socioeconomic characteristics and maternal intelligence. Future breastfeeding research needs to take into account these important influences on child cognitive development. In any case, breastfeeding should continue to be encouraged, as any improvements in children's cognitive abilities are only one aspect of the benefits it provides.'
* The UK Millennium Cohort Study is a nationally representative cohort study that is following the lives of around 19,000 young people born across England, Scotland, Wales and Northern Ireland in 2000-02. So far, these have been followed-up at ages 3, 5, 7, 11, 14 and 17 years.