The effects of breastfeeding on children, mothers and employers

The effects of breastfeeding on children, mothers and employers is a £240,000 project funded by the Economic and Social Research Council. This wide-ranging project is the most comprehensive study of its kind in the UK and is examining the effects of breastfeeding on children, mothers and employers.

A team of researchers at ISER and the University of Oxford is examining the relationship between breastfeeding and a child’s early development including early literacy and numeracy skills at Key Stages 1 and 2. It is also looking at whether there are links between breastfeeding and a child’s social development by examining areas such as hyperactivity and peer problems. The study is also exploring whether there are any links between breastfeeding and the health of mothers, for example in areas such as post natal depression, as well as the impact of family-friendly working practices on breastfeeding duration and the mothers’ decisions to return to work.

Data

The project is making use of two major data sets involving thousands of children.

The Millennium Cohort Study (MCS)

The MCS is a nationally representative longitudinal survey of over 18,000 children born in the UK in 2000 and 2001. Data were collected when the children were aged 9 months, 3 years, and at entry to primary school (age 5). The MCS contains information on the child’s birth, including factors correlated with breastfeeding initiation, such as the length of stay in hospital. There is detailed information on breastfeeding (71% of mothers breastfed initially, and 66% of those breastfed for 6 weeks or more), very rich data on the family’s socioeconomic status, and on the child’s cognitive and psycho-social development. Moreover, the MCS data can be linked to external data on the hospital where the child was born, allowing us to use hospital-level variables as a source of exogenous variation to explain breastfeeding initiation and duration.

The Avon Longitudinal Survey of Parents and Children (ALSPAC)

ALSPAC is a longitudinal study of around 12,000 children born in the Avon area in the early 1990s. Data were collected at four points during pregnancy and at several points following birth – from parents, the child him/herself, and the child’s teacher. Topic areas covered include physical and mental health, socioeconomic status, and child development; SATS results and school-level data are available via merged records. The data on breastfeeding are very rich: there are repeated questions on attitudes to breastfeeding, feeding practices, and the exact duration of breastfeeding (79% of mothers breastfed initially, and 60% of those breastfed for 6 weeks or more).

What the team are looking at

The research is looking at the effects of breastfeeding across a range of individual outcomes of a wide group of potential beneficiaries, including the child, the mother and her employer.

Cognitive development

Differences in children’s cognitive development emerge at early ages and this underlines the importance of timely parental investments. Breastfeeding is a very early intervention, and one where there is great scope to increase uptake. This project examines the relationship between breastfeeding and a range of indicators of cognitive development including parental and teacher assessments of children’s early literacy and numeracy skills, Key Stage 1 SATS scores, and other standardised tests.

Non-cognitive development

Recent research shows a significant impact of behavioural and psycho-social outcomes on earnings and education and indicates parental inputs as the most important determinants of non-cognitive development in children. This research focuses on the relationship between breastfeeding and aspects of psycho-social development including prosocial behaviour, hyperactivity, emotional, conduct and peer problems.

Maternal mental health

Conditions such as post-natal depression have an immediate impact on mothers and carry long-term risks for their future mental health. Depression among mothers is also found to have a serious impact on the cognitive, social and physical development of their children. The research is examining the link between breastfeeding and maternal depression, using repeated measures of maternal mental health, and detailed information on breastfeeding intentions and practices.

Mothers’ return to work and absenteeism

The case is often made that measures to promote breastfeeding among working mothers benefit employers by reducing turnover and absenteeism among workers. However, there are very few empirical studies which support these claims. This research combines the mother’s choice to breastfeed and the employer’s decision to introduce family-friendly working practices in a unified theoretical framework, and analyses mothers’ decisions to return to work after birth and their absenteeism rates.

Innovative methods

In research on breastfeeding, it is notoriously difficult to identify whether the observed relationships are causal, rather than arising because breastfeeding is more likely to be practiced by mothers whose characteristics (higher social class, higher IQ, higher education, etc.) favour more positive outcomes. As ethical considerations make it difficult to implement large randomised trials in this area, the most convincing attempts to circumvent this endogeneity problem have involved exploiting changes in maternity leave legislation or studying sibling pairs. In this research project we are making use of two methodologies – Instrumental Variables and Propensity Score Matching – and two large data sets to investigate the question of causality.

This project is innovative in four ways:

• It examines the effects of breastfeeding on a wide range of child outcomes which have been extensively linked to measures of adult economic achievement, including non-cognitive as well as cognitive child development.
• It explores whether breastfeeding has beneficiaries other than the child. In particular, it is studying the effects of breastfeeding on the mother, in terms of her mental health, and on employers, in terms of absenteeism and mothers’ return to work decisions.
• It assesses the extent to which the relationship between breastfeeding and childhood development can be given a causal interpretation. Our strategy consists of adopting two different approaches to the endogeneity problem, and using in each case the dataset which is best suited to the methodology.
• It examines issues of heterogeneity – that is, whether some mothers and babies stand to benefit more than others from breastfeeding. Many existing studies on breastfeeding are unable to do this because of small sample sizes; others focus only on pre-term or low birthweight babies. This study is based on large and representative samples of UK children and this allows us to explore differences in effects between women with different education and socioeconomic characteristics.