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A story has appeared on the nutraingredients website about US research that "benefits of breastmilk over infant formula are 'overstated'".

In the expectation that this will be seized on by sectors of the more mainstream media, here's a closer look.

For the media, Mike Brady, Campaigns and Networking Coordinator at Baby Milk Action said:

"There are many curious aspects to this research and the way it is being reported. The research looked at a set of historic data and found that overall breastfed children did significantly better than formula-fed children, but that is not the headline appearing around the world. 

"The researchers highlight that in a subgroup no benefits were found from breastfeeding, but look closely: they compared a child who may have only been breastfed once with a sibling who had no breastmilk at all and looked at things like their maths ability and vocabulary years later. Finding little difference between these children, they concluded that factors such as their parents' education have a bigger impact than how the children were fed. No kidding! Years of robust research on health outcomes is being cast aside for this? 

"They also draw conclusions about breastfed children having higher asthma rates, contrary to other research, but to do so they have to turn their previous logic on its head. The NHS review of this research points out that in the subgroup of brothers and sisters fed differently there was actually no difference between reported asthma outcomes. From this you could conclude the feeding method does not have an impact on asthma risks if you follow the same logic the researchers use for reading and maths ability etc."

Researchers found breastfed children did significantly better on 10 of the 11 outcomes studied

The researchers analysed 25 years of data gathered by other researchers following a group of people in the United States from birth. The study states:

"Results from standard multiple regression models suggest that children aged 4 to 14 who were breast- as opposed to bottle-fed did significantly better on 10 of the 11 outcomes studied."

However, reports such as nutraingredients have picked up on a different conclusion:

"Breastmilk may be no more beneficial than infant formula for 10 of 11 long-term health and wellbeing outcomes traditionally associated with breastfeeding".

So what is going on?

Headlines are based on an exceptional subgroup of children

Well, the researchers focussed in on data specifically relating to siblings who were fed differently. Amongst this subgroup of brothers and sisters they found the better outcomes for children who were breastfed became insignificant.

However, the researchers counted a child as breastfed if the mother "breastfed him/her for any length of time." 

 So in this subgroup a mother may have started to breastfeed her child, encountered problems, not had good support, and soon after introduced formula. For the researchers the child was breastfed, even if it had just one feed. Such a mother may then have used formula for other children straight away. Should we really expect these children to have signficantly different reading and maths skills years later?

The majority of the outcomes the researchers considered (8 out of 11) were to do with behaviour or school performance, such as maths ability and vocabulary. In the population as a whole, the breasfed children generally did better, but not in this subgroup.

A more reasonable conclusion might be that further research is needed into why mothers did not breastfeed all their children. The researchers simply say, "all of the scenarios we can call to mind in which siblings are differently fed favor the breastfed sibling." Really? How about: mother has a difficult breastfeeding experience that leaves her and her child distressed, so she switches to formula and then uses formula for her other children? That is all too common where breastfeeding support is lacking. There is no right to paid maternity leave in the US, so mothers are already up against it when caring for young children.

Research methodology flawed

The flaws with this research – and more so the headlines it has generated - are obvious by looking at what it actually involved. However, to check my understanding, I asked Professor Mary Renfrew, Professor of Mother and Infant Health at the School of Nursing and Midwifery, University of Dundee what she made of the study. She told me:

"The exposure measures for breastfeeding were very crude. There was no measure of exclusivity, for example."

She added:

"Families where one sibling is breastfed and another not are likely to be different from those where siblings are fed in the same way. For example, perhaps the breastfeeding experience was problematic resulting in other children being formula fed, or perhaps one child was sick/small and the mother was unable to breastfeed."

So is it really possible to draw conclusions from this subgroup? Well, headlines will soon be going round the world because of it saying "benefits of breastmilk over infant formula are 'overstated'".

The outcomes investigated are a curious selection - maths ability at 14 years old?

The list of 11 "health and well-being outcomes" investigated by the researchers is as follows:

Body Mass Index (BMI)

Obesity

Asthma

Hyperactivity Score

Parental Attachment

Behavioral Compliance

PIAT Math Skills

PIAT Reading Recognition

Peabody Picture Vocabulary Test

Weschler Intelligence Scale (WISC)

Scholastic Competence

Now, across the data as whole, remember, the researchers found breastfed children (even with their weak definition), "did significantly better on 10 of the 11 outcomes studied."

All but body mass index (BMI), obesity and asthma are behavioural or scholastic outcomes, where parental influence is going to be most significant - such as do they read to their kids. Even then, drawing conclusions on the first two of these three physical factors is a difficult task in a country with such an unhealthy relationship to food as the United States.

The researchers were looking at children aged 4 to 14 years old. The home environment and attitudes to food and exercise may outweigh the generally healthier growth profiles of breastfed children.

Remember, the US is a country where over 35% of the population are classified as obese and nearly 70% have a BMI that classifies them as overweight or obese. So even optimally breastfed children will be hard pressed to retain their advantages once they are immersed in a fast food culture and assessed years later.

See: http://www.cdc.gov/nchs/fastats/overwt.htm

Feeding method did not make a difference to risk of asthma in siblings fed differently

The findings for the subgroup of siblings who were fed differently have been used to generate the headlines about no supposed benefits from breastfeeding, despite the flaws described above.

Yet when it comes to asthma, the findings show that siblings fed differently had the same risk of asthma. So you could conclude the feeding method makes no difference to risk of asthma - just as the researchers concluded for the other outcomes. This is what the National Health Service for England and Wales says in its review of the research. See:
http://www.nhs.uk/news/2014/02February/Pages/Breast-milk-no-better-than-bottled-researcher-claims.aspx

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

When it comes to asthma the researchers change their focus to look at the population as a whole. The NHS says:

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. 

However, fears are not being allayed. This headline was reported in Brazil today: "Breastfeeding increases risk of asthma, Ohio researchers find."

Let us know what you think of this research and how it is being reported.

Colen, C.G., Ramey, D.M., Is Breast Truly Best? Estimating the Effects of Breastfeeding on Long-term Child Health and Wellbeing in the United States Using Sibling Comparisons, Social Science & Medicine (2014), doi: 10.1016/j.socscimed.2014.01.027.