Breastfeeding and child development
What is this research about and why did you do it?
This research estimates the effect of breastfeeding on child development: cognitive and socio-emotional, as well as health. Breastfeeding is just one of many ways in which mothers can influence their child’s development, and mothers who breastfeed may also be more or less likely to make other investments that affect their child’s development. Although there is much research on breastfeeding, most previous work does not isolate the effect of breastfeeding from these other investments undertaken by families.
How did you answer this question?
Our research found that, among a sample of low educated mothers, babies born just before or during the weekend were less likely to be breastfed compared to those born on weekdays, because UK hospitals reduce breastfeeding support at weekends. This allowed us to disentangle the effect of breastfeeding from other investments that improve child development, because mothers do not choose when to give birth, so the costs of other investments are uncorrelated with timing of birth. We combined this observation with the Millennium Cohort Study dataset, collected by the UCL Centre for Longitudinal Studies, which follows children born between 2000-02 and collects data on their development (including cognitive tests) every two to four years.
What did you find?
We found that breastfeeding for at least 90 days improves children’s cognitive development by around 0.46 standard deviations on average between ages 3 and 7, 95% confidence interval (+0.1 ; 0.82). Concerning the effects on socio-emotional development and health, our estimates are not statistically different from zero, though the confidence intervals are wide.
On the horizontal axis, 0 refers to birth deliveries taking place on Mondays at 00:01am, and 168 to those taking place on Sundays at 23:59 pm. The probability of breastfeeding(solid dotted line, measured in the right vertical axis) decreases with the proximity to the weekend. The average value of the child’s cognitive development according to timing of birth (solid line, measured in the left vertical axis) tracks how the probability of breastfeeding evolves with timing of birth, indicating a causal link between timing of birth, probability of breastfeeding, and child’s cognitive development. The predictive index (light grey dotted line), which only depends on the child’s and mother’s observed characteristics, does not track the probability of breastfeeding, confirming the validity of our research design as it shows that the relation between timing of birth, probability of breastfeeding, and child’s cognitive development is not due to differences in mothers’ and children’s observable characteristics.
What implications does this have for the research on wealth concentration or economic inequality?
Breastfeeding is far more common amongst highly educated mothers: according to the 2010 UK Infant Feeding Survey, 56% of mothers who left full-time education at 19 or over breastfed their children for at least four months, compared to 22% of mothers who left full-time education at age 16 or before. Given our new evidence that breastfeeding improves children’s cognitive development, it may be an important contributor to the inter-generational transmission of human capital and the perpetuation of inequalities therein.
What are the next steps in your agenda?
A vital question is whether the strong effects on cognition persist or fade out as children get older. We plan to estimate the longer-term effect of breastfeeding on children’s academic attainment, using data from formal school assessments, the General Certificate of Secondary Education (GCSE), which students sit at 16 years of age. We will use the linkage between the Millennium Cohort Study database and National Pupil Database administrative records for this.
Citation and related resources
This paper can be cited as follows: Fitzsimons, E., and Vera-Hernández, M. 2022. 'Breastfeeding and Child Development.' American Economic Journal: Applied Economics, 14(3), pp. 329-66.
Related resources:
- The pre-publication version of this paper is available online
- Listen to a Freakonomics, M.D. podcast on this paper (web, Spotify, Stitcher)
- Press coverage in The Guardian (1 July 2022)
- Radio coverage in BBC Radio 4's Woman's Hour
