Tag Archives: observational studies

Is breastfeeding all it’s cracked up to be?

Zoe Williams wrote an intriguing article in The Guardian that challenged some widely held assumptions and beliefs about the benefits of breastfeeding (‘The backlash against breastfeeding’). It did, as you might imagine, generate strong reactions from those who vehemently espouse that “breast is best”. It was written on the back of a recent front cover of Time magazine that caused an even greater furore (‘Are you mom enough’), which championed a form of ‘attachment parenting’ that encouraged breastfeeding until the child is well over one year old.

I did feel that Zoe Williams’ article raised some interesting points, some of which I wanted to address here.

But I also had the strong suspicion that the claims made for [breastfeeding’s] benefits – the higher IQ, the protection against obesity, the superior bonding, the warding off of disease both now and for ever, both for baby and for mother – were mostly bogus. A lot of the reasoning seemed syllogistic (babies born into low-income families end up fatter; low-income mothers breastfeed less than high-income mothers; therefore breastfeeding prevents obesity) or frankly lame.

This relates to the concept I’ve written about before, that correlation does not imply causation. As she quotes Joan B Wolf later in the article: “Breastfeeding cannot be distinguished from the decision to breastfeed, which could represent a more comprehensive commitment to healthy living.”  

While this is true, that is not to say that the researchers who conduct these types of observational studies are not aware of this limitation. It is hard to do interventionist, controlled studies, as you would do in a lab or in randomised controlled trials to test a new medicine. Imagine randomly assigning new mothers to one of two groups – breastfeeding or formula-feeding – and getting them to stick to this regimen so that you can measure the outcomes of the children. Not likely, which is why such interventionist studies have been limited (1 & 2).

So researchers work with the tools available to them. They try to include appropriate comparator groups and make statistical adjustments to account for potential confounding variables. Not perfect by any stretch, but the best available methods.

I knew a lot of mothers who formula fed; they didn’t seem to love their babies less.

Ignoring the submission to anecdote, which is a mortal sin to evidence-based thinkers, a more worthwhile point to address is an argument I’ve often heard that goes approximately: “Well, they say breastfeeding is best, but I formula-fed and my child turned out alright”.

There are two key flaws in this reasoning. One is that by advocating breastfeeding, it is implying that formula-feeding is bad. No. It’s just there’s less chance that any outcomes associated with breastfeeding will also be seen with formula-feeding. The second misconception is that there’s a complete separation, or dichotomy, between the two groups. But here we’re comparing averages of large study groups – there will be huge amounts of variability around the averages and a lot of overlap, and only the right statistical analyses can reveal any true differences.

Put simply, there will be mothers of formula-fed babies who form strong attachments (to carry on the example in the article) and mothers of breastfed babies who do not.

By analogy, there will be some people that do all the ‘right’ things – not smoke, eat healthily, exercise, apply sun cream – who will get cancer and there will those who smoke 40-a-day and drink to excess who do not. It doesn’t disprove the link, it’s all about stacking the odds in your favour.

(I should clarify that the evidence I’ve seen for superior bonding associated with breastfeeding is somewhat weak, but I referred to it here to address a more general point about the common use anecdotal evidence).

This struck me as a bizarre place to have arrived at; where even to talk about the evidence behind the benefits of one type of infant feeding over another is heretical.

Absolutely correct. We should constantly gather and scrutinise data, and if strong enough evidence emerges that contradicts our prior assertions, then we should be prepared to change our minds. I applaud the fact that this article was written, even if there are bits I wouldn’t necessarily or wholeheartedly go along with, as we should always be ‘talking about the evidence’.

The questioning of the orthodoxy is taken as a direct attack on babies.

[Charlotte Faircloth, sociologist]: “… Everything has got very heated, and very moralised. How you feed your kids is no longer a personal decision. There’s this idea that you can breastfeed your way out of poverty, or if you don’t breastfeed your kid’s going to be fat or have a low IQ…” She pauses. “It’s all got a bit out of hand.”

Williams is right that some breastfeeding advocates are evangelical and overly ideological about breast milk, to the point that some mothers feel over-bearing pressure to breastfeed. As Charlotte Fairclough is quoted, it’s a personal decision. Fairclough also touches on my earlier point that there’s no binary distinction in the outcomes of children who are breastfed and those who are not – breastfeeding doesn’t determine the outcome but may make it more probable (and, if it does, it will certainly still only be one factor amongst many).

Williams then quotes French feminist Elisabeth Badinter:

“when it’s recommended that you breastfeed your child for one year – six months exclusively, with nothing else, day and night, on demand – there are obviously consequences for a couple.”

“There are women for whom breastfeeding is a true pleasure. It’s very good for them and it’s very good for the baby. But to breastfeed a baby if the mother herself doesn’t like it? It’s a catastrophe. The decision to breastfeed is an intimate and private decision. No one should be able to interfere.”

In my mind, this touches on something I have written about before – that to lay down a hard-and-fast prescription for parents to follow is not always straightforward or productive. A more nuanced approach is often required that takes into account the familial circumstances and considers the parents’ well-being as well. It would be no good hectoring parents to follow a particular path, if it leads to a significant worsening of their own physical or mental health, especially if the knock-on effect is a deterioration in family relationships.

It seems highly unlikely that this would allow people to be good parents nor provide a decent environment for the child (a brief look at the scientific literature suggests this assumption isn’t entirely unreasonable, e.g. thisthis and this). It also risks attaching blame to a parent for any perceived character flaw in their child, and guilt-tripping parents in this way seems a counter-productive approach.

The research about ear infections, respiratory disease and diabetes is very mixed. Neither fussiness around new foods nor constipation are classic or very salient markers of good health. The obesity studies are debatable. The weight loss of breastfeeding mothers is taken from a WHO report, based on two interventionist studies in Honduras. It’s nothing like that straightforward: it does use 500 calories a day, but if your appetite increases at the same time, it is amazing how quickly and easily you can pop 500 calories into your mouth. Meanwhile, Wolf points out, no study on maternal cancer has “distinguished the effects of breastfeeding from the behaviour of women who breastfeed”

Again, I agree, it’s not straightforward! But I would, perhaps, strike a more positive tone.

The studies aren’t perfect (Williams also quotes the American Academy of Paediatrics: ‘There are a lot of methodological problems’), but that’s no reason to just give up on evidence altogether. The best available evidence, as far as I can see, is saying that breastfeeding is likely to bring a range of benefits to the child, and possibly some to the mother. A Cochrane Review from 2009 includes many citations that support various benefits of breastfeeding, as well as a discussion of some of the uncertainties.

I also agree that the weight loss data must be taken in context, such as whether you are dealing with developed or developing countries, and some effects, such as iron status, can be achieved through supplementation. So, in some instances, there’s no need to be over-zealous about breastfeeding, as long as adequate healthcare advice is in place.

“The notion of risk [has been] transformed from a dichotomy to a continuum.” It’s no longer a case of “safe” versus “dangerous”; rather, everything carries some risk and you announce your fitness as a parent to the world by interpreting hazards in the most credulous, fervent way. The onus isn’t on the researcher to prove the point any more – the onus is on the parent, or parent-to-be, to prove that they’ll believe the researcher.

I’m not sure this is true and seems an over-generalisation. There’s a huge variety in parental attitudes and some are incredibly questioning, and whether and how this has changed in recent years is uncertain without any data. I think it misrepresents the role of a researcher, too – that the onus is on them to ‘prove a point’. Scientists don’t (or shouldn’t) undertake work to prove already held beliefs, rather they formulate hypotheses and design experiments to support or reject those theories.

There are lots of other points in and around the ones I’ve highlighted, a lot of which veer from my intention to address evidence-based decisions, but I do encourage you to read the whole article for some interesting discussion of feminism and social policy.

I’ll summarise by saying that I would still state that breastfeeding can potentially bring a range of benefits over formula-feeding, because that is where the balance of scientific evidence is, with little or no contrary evidence to dissuade me yet. And this should be reflected in the healthcare advice that is provided. I absolutely agree, though, that foisting this decision on mothers is, at best, unnecessary and, at worst, damaging. Healthcare advice must take context into account.

On a more general point, I welcome any sensible, critical look at the evidence behind claims, as Zoe Williams has done. It’s certainly made me re-evaluate – and in some instances, such as in the link to lowered risk of maternal breast cancer, made me temper – my own standpoint on the benefits of breastfeeding.

A final point, though. It was disappointing that an article that relied so heavily on rejecting or challenging some of the evidence that is used to promote the “breast is best” standpoint, did not once link to any primary research. A few quotes here and there from, no doubt, serious academics, and a link to a book, but nothing that could point the reader to the original research studies.

It is perennial complaint that evidence-based advocates level at popular journalists, so I don’t want to single out this author for special criticism. But it is something that could do with a cultural shift and, perhaps, mainstream commentators will start to follow the examples of their science colleagues.


Hat-tip to Mum-in-law, Jenny, for The Guardian article.

Demanding babies and fraught mothers

There was quite a bit of coverage at the end last week about a report published by Essex and Oxford-based researchers that looked at the effects of on-demand feeding versus scheduled feeding. The researchers analysed just over 10,000 thousand babies born in the 1990s and checked whether babies fed in a particular way at 8 weeks and 33 months achieved better academic results later in their lives and whether the well-being of the mothers was affected.

The authors of the study reported an association between being fed on-demand as a baby and higher IQ scores at 8 years and better SATs exam scores at 5, 7, 11 and 14 years. This held true for breastfed and bottle-fed babies. Another effect they uncovered was that mothers who fed on-demand reported lower confidence, higher fretfulness and worse sleep patterns.

Photo by Anton Nossik*

Now I’ve mentioned quite a few times the mantra that “correlation does not imply causation”, and so my immediate reaction to seeing this in The Guardian was ‘here we go again’. Journalists often overlook the limitations of correlative studies in favour of neat and tidy story – after all, “this behaviour causes this effect” has a bit more punch than “this behaviour is associated with this outcome, but it may be acting through a third or multiple independent variable(s)”.

For an entertaining and revealing example of this issue, I would recommend reading stand-up mathematician Matt Parker’s ‘mobile phone masts cause increase in birth rates’ hoax story.

My first thought when my wife told me about this story was that, rather than on-demand feeding directly causing the higher IQ scores, it could equally be that a third factor was at play. As a speculative example, it could be that an attentive personality primes a mother to feed on-demand and also, independently, to spend more time with their child on educational development. This is an important distinction because it would mean that mothers wouldn’t be able to improve their child’s academic chances by feeding on-demand, rather they would have to pay more attention to educational development.

The authors were well aware of possible confounders and tried to take into account other differences between the groups to narrow down the possibilities as much as possible. This involved adjusting for family income, the education level of the parents, different parenting styles, the age and sex of children, and general maternal health. After all this, there was still a significant difference – children who were fed on-demand as babies had, on average, IQ scores 4 points better than children who were fed to a schedule.

This study has an advantage over many other correlative studies in that a third group presented itself – mothers who wanted to feed to a schedule but were unable to and so fed on-demand, i.e. they wanted to be in one group (scheduled feeding) but ended up as if they were in the other group (on-demand feeding). Crucially, the children in this third group achieved the same elevated academic achievement as seen in the other on-demand group.

Photo by Tom Carmony**

This meant that the authors were able to suggest that the improved academic outcomes weren’t due to having the type of mother who wishes to feed to a schedule, but that they were due to the actual act of being fed on-demand. This relies on an assumption that the mothers in the scheduled feeding group and the attempted scheduled feeding group had similar characteristics, and would therefore have similar approaches in other ways that may affect educational development. This may not be entirely true as other, more subtle differences could exist between these groups, but it’s a tantalising result that merits further investigation. I guess measuring the amount of time spent with the child on learning and development would be something at which to look.

There will still be other factors at play and it is still essentially a correlation, but it starts to narrow down the possibilites. The authors themselves admit the limitations in their study, with the lead author Dr Maria Iacovou telling Science Daily:

“At this stage, we must be very cautious about claiming a causal link between feeding patterns and IQ. We cannot definitively say why these differences occur, although we do have a range of hypotheses. This is the first study to explore this area and more research is needed to understand the processes involved.”

Dr Iacovou was also fairly even-handed on Channel 4 news, rightly highlighting that we still don’t know the mechanism for the observed effects and this is really the first step in establishing a causal relationship.

The final thing to note about the study, is that it was gratifying that the researchers looked at both sides of the issue – the outcomes for the baby (IQ, academic achievement) and the mother (well-being indicators). I’ve written before about the importance of looking at all knock-on effects, as it can be counter-productive to focus solely on the baby if it means a serious detrimental effect on the mother’s mental health.

If on-demand feeding really does drive academic development, then implementing a healthcare strategy to encourage this must take into account the negative impact this may have on the mother and include an appropriate support mechanism. Otherwise, the effectiveness of the intervention will be limited, as mothers will be more likely to give up in favour of a reassuring routine.

As Dr Iacovou said, “mothers are people too”.


Hat-tip to mum-in-law Jenny who sent me this story.

*CC licence: http://creativecommons.org/licenses/by/3.0/deed.en

**CC licence: http://creativecommons.org/licenses/by-nc-nd/2.0/deed.en_GB

On the benefits of breastfeeding (and getting the policy right)

Certain benefits of feeding children with breast milk over modified cow’s milk (‘infant formula’) have been well established, such as bolstered immunity, reduced risk of diabetes, and a lower risk to the mother of developing breast cancer. A recent article in the Observer introduces the possibility of an extra benefit of breast feeding, in that it could boost a child’s later cognition (as measured by IQ score). This is likely to be of interest to any parent wanting to help their child acquire the proper mental faculties to lead a fulfilling life.

by Flickr user: muskva*

This newspaper story, however, brings to bear some important cautionary tales. First of all, the types of studies the researchers have assessed mean results should be treated with a note of vigilence. It is unclear from the article whether the conclusions are based largely on the quoted researcher’s own research or a synthesis of past, published work conducted by others (more on that later), but the Institute for Social & Economic Research’s own website suggests that this is based on primary research. The Observer article does, however, indicate that the researchers analysed “studies in the fields of epidemiology and public health”. It is likely that these would have been observational studies, where the cognitive abilities of children from groups of women who had chosen to breastfeed their babies are compared with the IQ scores of children from other groups who had chosen to use infant formula. The Essex and Oxford researchers in the article appear to claim that those children who were fed breast milk, on the whole, outperformed those children who were fed formula milk. On the face of it, a neat result.

But that brings us back to familiar adage that correlation does not mean causation. It doesn’t take much scrutiny to realise that if children from more affluent families are more likely to breastfeed, then simply growing up in more comfortable, less stressful and education-rich environment could easily account for the improvement in cognitive abilities. The team that carried out the work are clearly aware of this, and claim to have corrected the data to eliminate the effects of other factors such as the family wealth, but this always introduces additional sources of potential error. This doesn’t make the research any less worthwhile, only limits the conclusions that can be drawn from it.

These types of study are often one of the first type to be done on human populations and it emphasises the experimental boundaries. If this sort of question were to be asked for, say, a rodent, the researchers could take a group of animals from the same population and split them equally into two groups. Each group could be raised in controlled environments that are identical to each other (temperature, access to food/water, number of companions, etc.). The only variable would be that one group would be suckled with mammary milk and the other fed with milk from another source. Any difference in the performance of the offspring in subsequent behavioural tests could suggest that it was down to the mammary milk. It wouldn’t prove it, though, as it could be more subtly due to increased mother-baby contact or an unknown variable, but it would be an interesting result that would warrant further investigation.

It is, understandably, improbable that this kind of experiment would be done in a human population – who could convince a mother to agree to be randomly assigned to one of two groups, breastfeeding or non-breastfeeding? – and so investigators have to use the next best thing. This could lead to targeting interventions or different levels of support at two or more groups from the same socioeconomic background and seeing whether that affects children’s IQ scores, which would allow comparison of women from the same group but receiving different treatment. But, again care needs to be taken to eradicate or account for potential confounding factors.** These limitations bedevil many researchers trying to find out more about factors affecting child development and is part of the reason why much of the guidance about parenting is not evidence-based or is, at best, based on suggestive findings.

Anyway, the second cautionary tale comes from the way the evidence is presented. The newspaper article states that the scientists are to present their findings at a policy conference. Conferences are the vital arenas at which researchers’ current theories are presented to and subsequently challenged (robustly!) by their colleagues. Many a hypothesis has been revised, re-interpreted or rubbished at a conference. Many pieces of work, such as that in the Observer article, will not have even been published in a peer reviewed journal. This means that it has not been formally reviewed and accepted as scientifically valid by other experts in the research field.

Even after this assessment and publication by a scientific journal, it is still only one piece of evidence in a vast sea of scientific work. It often takes a review of several scientific studies tackling the same research question before any firm conclusions can be made. So with this appreciation of the scientific process, the claims in the Observer article start to look less conclusive as the headline would suggest. As I mentioned earlier, the researchers are well aware of the caveats, but a casual reader may not be. It took digging beyond the article, to the ISER’s website, before I could determine the nature of the research, as the article didn’t link to anything other than more guardian.co.uk articles.

This is a problem that is widespread in science reporting – bold claims in newspapers are often based on tentative evidence, unpublished findings or misleading press releases (see ‘churnalism’) – and is a particular problem when it comes to parenting, as it can instantly affect the decisions parents make. One only has to look at scare stories about pregnant women’s sleeping position and the risk of miscarriage, vaccine safety, mobile phone use, plus countless other examples, to see the difficulties people face in picking out the sound evidence.

It is also problematic because evidence presented in the media can influence public opinion and the policies introduced by governments. Looking back to the breastfeeding story, if it is genuinely that the act of breastfeeding or a component of breast milk that boosts the chances of a child having improved cognitive scores, then the government may wish to look at improving breastfeeding support programmes. If, on the other hand, the major influence turns out to be the societal factors, then this would require a broader set of interventions that tackle social deprivation.

A further issue with policy documents, such as the one mentioned in the Observer, is that they circumvent the usual quality control for scientific research. They are often not published in peer reviewed journals and, as such, not subjected to the same rigour or openness as work that has been critiqued by other experts in the field. This opens up the possibility of a greater degree of bias and subjectivity. In this case as well, the report is not yet available (only a working paper) so the general public has to largely rely on the media’s reporting of researchers’ interpretations, something that is riddled with potential problems.

For the record, the Observer article seems fairly non-sensational – the headline is probably overly-conclusive, there’s a lack of linking to information about the conference and research, and the caveats could be included.

The causes and consequences of speculative science reporting have been dissected brilliantly elsewhere (see Martin Robbins of The Guardian on the subject and Brian Switek at wired.com for a recent example), so I will summarise by saying that it is incumbent on scientists to not inflate the nature of their findings for the sake of publicity, the universities or research institutions to issue balanced press releases, and for science journalists not to over-spin the story.

Not that I’m asking too much.

*(under Creative Commons licence, some rights reserved: http://creativecommons.org/licenses/by-nc-sa/2.0/deed.en)

**Interestingly, another recent research article does point towards a causal link of breastfeeding with infant IQ, by seeing whether the same trends are apparent in both high-income and middle-income populations