Tuesday May 10 2011
The study did not assess why some women did not breastfeed
“Mums should breastfeed for at least four months to avoid having naughty kids,” reported The Sun.
The news report is based on a large study into whether the duration of breastfeeding is associated with a child’s risk of behavioural problems at age five. The study looked at behavioural problems, rather than just general naughty behaviour as might be thought from the newspaper headline. Children who had breast milk for more than four months were 33% less likely to have behavioural problems than those who had never had breast milk.
The study has several strengths, but also some limitations. It did find an association between breastfeeding and behaviour, but cannot show that one directly causes the other. Both infant feeding patterns and child behavioural problems are influenced by many different factors. Many of these were taken into account in the analysis, but the study did not assess whether mothers who did not breastfeed could not or chose not to, and it is possible that other confounding factors could have had an effect.
Breastfeeding has many benefits for both the mother and baby. Current guidance encourages women to ideally breastfeed exclusively for the first six months of life. See our breastfeeding guide for more information.
Where did the story come from?
The study was carried out by researchers from Oxford University. Funding was provided by the Policy Research Programme at the Department of Health, UK. The study was published in the (peer-reviewed) medical journal Archives of Disease in Childhood.
The BBC News reported this story well, highlighting in its headline that this study assessed the risk of behaviour problems rather than the general naughty behaviour implied by some of the other newspapers.
The Sun’s headline “Breastfeed 4 months or child will be bad” could cause undue distress for some mothers. The rest of the newspaper reports were generally accurate.
What kind of research was this?
This prospective cohort study examined whether breastfeeding is associated with a child’s behavioural development and their behaviour at age five.
The researchers say that it is natural for all children to occasionally behave inappropriately and have a temper tantrum from time to time. They were specifically interested in inappropriate behaviours that occur repeatedly over a period of time, interfering with the child’s or their families everyday life and having a negative impact on the child’s development. Behavioural problems may include excessive clinginess and anxiety, hyperactivity or conduct problems, such as lying or stealing.
The researchers speculate on how breastfeeding may be linked with fewer behavioural problems. They say that breast milk may contain essential fatty acids needed for brain development, or that breastfeeding involves more mother-baby interactions and better communication.
A prospective cohort study can only show associations between things – in this case baby feeding and later behaviour. However, it cannot conclusively demonstrate that one caused the other.
What did the research involve?
The study used data from the Millennium Cohort Study (MCS). This was a survey of infants born in the UK during a 12-month period in 2000-2001. The study included mother-child pairs who had participated in an assessment when the babies were nine months old, and another assessment when the child was five years old. The study only included white mother-child pairs. The researchers excluded children who were born extremely prematurely, and twins and triplets as their behavioural development may differ from singleton children. In total, data from 10,037 mother-child pairs was available.
At the nine-month assessment, women were asked whether they had ever tried to breastfeed their baby and, if so, the age of the child when they were last given breast milk. Additionally, the mothers were asked when the child had first been given formula milk, other types of milk and solids. Breastfeeding was defined as exclusive if the infant had received only breast milk, and no other milk solids or fluids other than water. Breastfeeding was categorised as never, less than two months, 2 to 3.9 months or more than 4 months.
A total of 512 children had been born prematurely (prior to the 37th week of pregnancy). As infant feeding and behavioural outcomes may have been affected by premature birth, these children were assessed separately from the children born at full term. As there were fewer premature children, they were divided into two breastfeeding categories: those who had been breastfed for less than 2.9 months, and those who had been breastfed for more than 3 months.
Behavioural problems were assessed when the child was five years old, using a validated questionnaire called the Strengths and Difficulties Questionnaire (SDQ). This consists of 25 parent-rated statements in five areas of child behaviour designed to identify children with behavioural problems. The researchers defined cut-off points where behaviour was considered problematic. According to this categorisation, about 10% of the children had problematic behaviour.
As there are other factors that may influence a child’s behavioural development, the researchers collected information on potential confounders. These included household socioeconomic position (SEP), the mother’s mental health, the mother’s age, education, whether she smoked or consumed alcohol during pregnancy, her relationship status and whether the baby had been admitted to a neonatal unit. They also assessed mother-baby attachment, whether the child was a first child or had older siblings, the type of childcare the child attended, and the age at which the child started childcare.
What were the basic results?
The researchers found that in both the term and preterm children, around 65% of mothers initiated breastfeeding. Of the full-term babies, 29% were breastfed for at least four months compared to 21% of the preterm babies. For women who breastfed for more than four months, the average length of breastfeeding was between 9.6 and 9.8 months. At five years, 15.2% of children in the preterm group and 11.9% of children in the term group had abnormal SDQ scores that indicated problem behaviour.
When the scores were adjusted for all potential confounders, children born at full term, and exclusively breastfed for over four months were 39% less likely to have behavioural problems than those who had never been breastfed (odds ratio [OR] 0.61, 95% confidence interval [CI] 0.45 to 0.83).
Children who were breastfed for more than four months but not exclusively (meaning they consumed other fluids or solids), were 33% less likely to have behavioural problems than children who had never been breastfed (OR 0.67, 95% CI 0.54 to 0.83).
For children who were breastfed for less than four months, there was no difference in the likelihood of behavioural problems compared with those who had never received breast milk.
For preterm children, being exclusively breastfed or non-exclusively breastfed for more than three months did not reduce the odds of developing behavioural problems (OR 1.20, 95% CI 0.45 to 3.22, and OR 1.02 , 95% CI 0.44 to 2.37, respectively).
How did the researchers interpret the results?
The researchers said that their findings “suggest that longer duration of breastfeeding (at all or exclusively) is associated with having fewer parent-rated behavioural problems in term children. The evidence for an association between breastfeeding and behavioural problems in preterm children was unclear”.
This large prospective cohort study found an association between breastfeeding for more than four months and a decreased likelihood of problematic behaviour at the age of five. One of the study’s strengths is its large size (in more than 10,000 mothers and children) and that the analysis took into account a large number of potential confounders that could influence infant feeding patterns and child behaviour. However, there are various limitations to this type of study, some of which the researchers highlight:
- The researchers say that although asking mothers to recall how long they breastfed their baby is reasonably reliable, there may be some bias as mothers may not recall accurately or may want to give the interviewer what they consider to be a “socially acceptable” answer.
- Owing to the small number of preterm children available to the study, the researchers could only look at two categories of breastfeeding duration, unlike the term children who they could categorise into three groups as there was a larger number.
- The study only looked at white mother–child pairs, so the findings do not represent the UK population as a whole.
- The researchers only looked at singleton pairs, and it is not clear whether breastfeeding is associated with behavioural outcomes in twins or triplets.
- The study did not assess the reasons why women did not breastfeed, i.e. whether this was by choice, or because the woman had problems with breastfeeding, or due to practical reasons, such as needing to return to work. Investigating reasons for not breastfeeding may have identified other confounding factors that could have influenced the child’s development.
This study demonstrates that breastfeeding after four months may be associated with a lowered risk of behavioural problems, but more research is needed to see why this may be the case.
Current UK NICE guidance suggests exclusive breast milk for the first six months of life. After this time, it is recommended that breastfeeding should continue for as long as the mother and baby wish, while gradually introducing a more varied diet. For more information, read the NHS Choices Breastfeeding guide.