Is breast milk really best, American study asks

"Breast milk is 'no better for a baby than bottled milk' and it increases the risk of asthma, expert claims," reports the Mail Online. The news comes from a large US study of children aged 4 to 14 looking at whether breastfeeding is associated with better health and academic outcomes.

The researchers argue that the majority of mothers who choose to breastfeed in developed countries are white middle-class women. It could be that this privileged position in society, rather than breastfeeding itself, accounts for the improved outcomes claimed to be associated with breastfeeding.

They found that overall, breastfed children had statistically better outcomes in 9 out of 11 areas. Unexpectedly, an association between breastfeeding and higher rates of asthma was also found.

But when they looked at children from the same family who had been fed differently (one bottle-fed, one breastfed), they found no statistically significant differences in outcomes for breastfed and bottle-fed children.

The researchers conclude that there is little evidence that breastfeeding improves outcomes. However, it is more likely that the influence of the children's genes and environment played a bigger role than whether or not they had been breastfed.

There is conflicting previous research looking at the association between breastfeeding and asthma, but the Department of Health and Asthma UK recommend breastfeeding where possible. Although breastfeeding is still the preferred option, the lack of a significant difference between siblings who were fed differently seen in this study should allay maternal fears if they are unable to breastfeed their baby.

Where did the story come from?

The study was carried out by researchers from the department of sociology at Ohio State University and was funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development.

It was published in the peer-reviewed journal, Social Science and Medicine.

The Mail Online generally reported the story accurately.

What kind of research was this?

This was a cohort study that used data from the US National Longitudinal Survey of Youth (NLSY). It aimed to see if breastfeeding made a difference to outcomes for children between the ages of 4 and 14 after socioeconomic factors were taken into account.

As this was a cohort study, it can only show an association and cannot prove that breastfeeding was the cause of any differences found. These could be related to other factors called confounders. The only way to prove causation is to conduct a randomised control trial, but this would be unethical.

What did the research involve?

The researchers took the NLSY data and studied physical, behavioural and academic outcomes to compare children who had been breastfed or bottle-fed. They then compared the results of the whole sample – sibling samples and "discordant siblings" (siblings who had been fed differently) – to determine if the differences were because of breastfeeding or socioeconomic factors.

They looked at data from 8,237 children who were born after 1978, interviewed (or their parents) between 1986 and 2010. Twins and triplets were excluded. Two subgroups of this sample were analysed:

• 7,319 siblings (more than one child per mother)
• 1,773 discordant siblings (siblings who were fed differently as babies)

The researchers say that studying discordant sibling data (within the same families) should eliminate socioeconomic status from having an effect on the results.

They also wanted to see if differences could be seen in later childhood, so looked at data from the age of 4 to 14 in terms of:

Physical health:

• body mass index (BMI)
• obesity
• asthma

Behaviour:

• hyperactivity
• parental attachment
• behavioural compliance

Academic achievement:

• reading comprehension
• vocabulary recognition
• maths ability
• memory-based intelligence
• scholastic competence (academic performance)

They analysed the data to take the following confounders into account:

• child age
• maternal age
• birth order
• marital status
• region
• maternal smoking and alcohol use during pregnancy
• prenatal care
• maternal educational achievement
• total family income
• maternal employment status
• insurance coverage

What were the basic results?

All three groups were comparable for the variable factors listed above. In the whole group sample, breastfed children had statistically better outcomes in most areas after adjusting for confounders. However, there was an association between breastfeeding and asthma, and there was no difference in parental compliance.

In the sibling sample – chosen to see if having a sibling made a difference to the results – the findings were similar. But there was no statistically significant difference in hyperactivity, attachment and scholastic competence, although compliance was better in the breastfed children.

When only discordant siblings were analysed, there were no statistically significant differences in any outcomes between breastfed and bottle-fed children, including for asthma.

How did the researchers interpret the results?

The researchers concluded that these findings "suggest that the relationship between breastfeeding and long-term childhood outcomes may not be as consistent and straightforward as once thought … The risks associated with a failure to breastfeed are drastically overstated…

"Once between-family differences are taken into account, we find relatively little empirical evidence to support the notion that breastfeeding results in improved health and wellbeing for children between 4 and 14 years of age."

Conclusion

This study does not alter the current body of research, which has shown the beneficial effects of breastfeeding. There were statistically significant differences in health, behaviour and academic outcomes in the full cohort, although there was an association between breastfeeding and asthma.

It is unclear why this reverse trend was found in this study, but it does not show that breastfeeding causes asthma or that bottle feeding prevents it.

The study did not show a significant difference between siblings within a family who were breastfed. This may be because genetic and environmental factors have more influence on these outcomes than breastfeeding at an individual level.

There are a number of confounding factors that were not adjusted for in this study, including the reasons for changing the feeding style within a family. There could have been maternal factors, such as breast disease, or an inability for the baby to breastfeed, such as a cleft palate.

Another factor to consider is that women are only offered unpaid maternal leave in the US. This could mean that the majority of women who can afford to take time off to care and breastfeed their baby are on a high income. It could be the case that breastfeeding would still be of significant benefit for children born to women on a lower income in the UK.

Other important childhood outcomes in which breastfeeding has previously been found to be beneficial were not measured, including allergies, immune status and diabetes.

Importantly, breastfeeding also brings benefits to the mother, such as reducing the risk of breast cancer and ovarian cancer.

Breastfeeding is still the preferred option where possible, the benefits of which have been confirmed by this study. However, as the study acknowledges, some mothers are unable to breastfeed for a range of reasons and it is important that they are not stigmatised. 

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