Tag Archives: confounding factors

Does breastfeeding ‘cut leukaemia risk’? No good evidence

Occasionally my work and home life collide – I read some stories in the press about research claiming breastfeeding for six months or more could cut the risk of childhood acute leukaemia. The research was shaky, so I wrote this for the Leukaemia & Lymphoma Research blog (where I work).


 

Reports coming out in the media (such as Express, Mail, Mirror) are suggesting that breastfeeding for six months or more can lower the child’s risk of developing leukaemia. But where did these findings come from and how reliable are they?

In this post, we take a look at the research that led to these reports, and suggest that the results are not very robust, the conclusions are overstated and the claims likely to cause unnecessary alarm.

Greater than the sum of its parts?

The new research, published in the peer-reviewed journal JAMA Pediatrics, combines many previous studies that looked at whether children who had been breastfed (and for how long) went on to develop childhood leukaemia. The studies in the new analysis were a mixture of size and quality, so on their own couldn’t lead to any definitive conclusions. But when put together and re-analysed – known as a meta-analysis – it is intended to boost the power of the findings.

The new study includes 18 studies that met a certain quality threshold. The researchers, based at University of Haifa in Israel, report that children who had been breastfed for six months or more had up to a 19% lower risk of developing leukaemia than children who had never been breastfed or had been breastfed for under six months.

From this, they conclude this is sufficient evidence of a protective effect to further promote the health benefits of breastfeeding and encourage greater uptake amongst new mothers.

But we are not persuaded these claims truly stack up.

Correlation is not causation

The strength of a meta-analysis is that it tries to make sense of all the best research on the subject. But all of the studies within the new analysis looked at the association between breastfeeding and leukaemia, and therefore cannot tell you about true causes. Other background factors that affect both the likelihood of breastfeeding and leukaemia risk could have been missed or overlooked.

For example, parental affluence may affect the decision to breastfeed. But affluence will also affect a host of behaviours, like attendance at nursery, exposure to infections, decision to vaccinate, time of weaning, and many, many more. We don’t know for sure what factors do influence leukaemia risk – and parental affluence is just given as an example here merely to illustrate the complexity of background factors – but simply linking breastfeeding and leukaemia risk without consideration of other potential influencing factors is far too premature.

Experts who conduct these types of studies are well aware of these issues and always attempt to account for background factors, like socio-economics, lifestyle, gender, ethnicity, and so on, but it’s always hard to eliminate them altogether. Nevertheless, we were alarmed when we spoke to our statistical experts who noticed that the meta-analysis unusually relies on crude data that did not appropriately account for background factors.

They suggested that the authors’ relative inexperience with this type of analysis has led to a number of flaws.

Hidden biases

The experts we spoke to pointed out a gross error in the data – one dataset, that had been used in two different publications, is included twice. This could distort the statistical robustness or the size of any effect, and could be serious enough to consider a correction or withdrawal of the paper.

There are also a few ways these data could have been skewed to give wrong or exaggerated results. One is a bias in those participating in these studies. Many were based on phoning mothers at home or by a self-administered questionnaire. This introduces a potential participation bias, where the people surveyed and who agreed to take part were not representative of the population as a whole. This may mean certain groups, such as more educated or time-rich parents, were overrepresented in the comparison group (children who didn’t get leukaemia), suggesting a larger proportion of children who did not get leukaemia were also breastfed.

Almost all of the studies asked mothers or parents to remember the duration of breastfeeding, sometimes many years later. This introduces a possible recall bias, where parents may not have accurately remembered what they did or their responses were affected by knowing that their child had had leukaemia. And because childhood acute leukaemia is thankfully relatively rare – only three to four children in every 100,000 are affected each year in the UK – the small numbers could have inflated these biases.

It would be far better to recruit a large random sample of people, collect data in real-time, and then look at whether children went on to develop leukaemia. This is more costly and time-consuming, but it would help diminish some of these potential biases because the particpants and research questions would be defined up-front. 

The authors acknowledge these limitations in their discussion section of their paper, which is why we were surprised by the strength and certainty of their claims in the conclusions section.

What would this mean in the real world anyway?

There is some evidence that links proper immune system development to a reduced likelihood of developing leukaemia as a child and certain genetic faults present at birth can raise the risk substantially, but we are still far from truly understanding all the many different factors at play. It is an important area to be able to understand who is most at risk and what factors can alter their likelihood of developing this disease if we are to prevent some of these cases, but we are not convinced that this new analysis provides strong evidence for a significant role of breastfeeding.

We should also stress that because of the relative rarity of childhood leukaemia, even if the authors’ claims were true, it would still affect only a tiny number of children. And it would still only affect children who are already at risk because of key genetic faults that occur in the womb.

There is a lot of pressure on new mothers, some mothers cannot breastfeed and many factors can affect how long new mothers can breastfeed for. Parents of children who develop leukaemia can also feel a lot of guilt, even though we know some children will unfortunately get the disease whether they’ve been breastfed or not.

Stories based on problematic research do not help anyone.

  • For some expert opinion, including our Research Director and Prof Eve Roman (an epidemiologist whose work we support), see the Science Media Centre
  • Reference: Amitay & Keinan-Boker (2015). Breastfeeding and Childhood Leukemia Incidence A Meta-analysis and Systematic Review. JAMA Pediatr. 2015;169(6):e151025. doi:10.1001/jamapediatrics.2015.1025
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“It must be his teeth”: teething symptom myths

I wrote some time ago about how our little one was teething and the measures we’d taken to alleviate his discomfort. Well, this little chapter is still in full swing, with a mere two teeth erupted so far. But this isn’t a place to write long diary entries detailing my child’s progress; instead, I want to bring some science to light.

I’ve heard a number of physical signs regularly attributed to teething, such as rosy cheeks, diarrhoea, green faeces, fever, gnawing, irritability and drooling to name a few. It seems these beliefs are fairly common, as surveys of parents and health professionals have shown.

It gets interesting, however, when you look at some of the research done in this area. There seems to be some disagreement over which symptoms are actually caused by teeth eruption, and whilst it’s clear that individual babies will display different teething signs, it’s also apparent that some beliefs are not borne out by the evidence.

One of the difficulties is that the onset of teething (6-12 months) often occurs around the same time that babies become particularly susceptible to a variety of infections and upsets. This is mainly due to the decline in immunity imparted by maternal antibodies, as well as changes in behaviours that see infants actively interact with their environment.

There certainly seems a fair amount of evidence that many signs assumed to be caused by teething are actually caused by something else, such as meningitis, bacterial infection and herpes simplex virus infection. As the NHS Clinical Knowledge Summary bluntly puts it: “Teething does not cause children to become systemically unwell”. 

Another problem is our familiar foe: limited experimental design. Studies in this area are rather limited in number, often rely on self-reporting rather than objective measurement, deal with correlations not causations, and many look back at clinical data rather than tracking babies as they develop. These complications may be exacerbated by the fact that many health professionals hold erroneous beliefs too, which influences the data collected.

So what do we know?

Symptoms often misattributed teething:

  • Diarrhoea: This is one of the most common symptoms attributed to teething, but no solid data exist to suggest this is due to teething in the majority of cases. It has been tentatively suggested that slightly looser stools may occur during teething and this could lead to mild nappy rash.
  • Fever: Teething may cause a small rise in body temperature, but a feverish temperature above 38°C is unlikely to be due to teething.
  • Runny nose: The jury’s out on this one, but the reported associations are weak and this symptom is more likely to be a due to a wider problem.
  • Wakefulness: While teething may cause some disruption of sleep, this is probably over-exaggerated by parents, and may be partly down to changing sleep patterns and the formation of attention-seeking habits. I was also told by a midwife that teeth move more during the night, causing greater wakefulness – I initially thought not, as it seems more reasonable that the distress is apparent when there isn’t anything to distract the infant. Any data on this latter point would be gratefully received!
  • Green faeces: This is one I’ve heard a number of times, sometimes with an explanation of a change in the stomach acid balance. I can’t find anything in the literature (but please come forth and proffer!) but, on the face of it, it doesn’t seem to chime with idea that teeth eruption does not cause systemic upset.

 Symptoms more likely to be caused by teething:

  • Drooling: Excessive saliva can form and this may be seen by an infant dribbling more than usual. This isn’t conclusive, though, as salivary glands become active around 2–3 months of age and constant drooling can be expected then.
  • Gnawing: Teething infants may gnaw on cold, hard objects or on their fingers to temporarily help with teething discomfort.
  • Mild irritability: The pain associated with teething, which is mostly associated with an inflammatory response within the gums, might cause grizzliness, disturbed sleep, ear rubbing and a decreased appetite.
  • Rosy cheeks: This is some support in the literature that flushed, red cheeks are associated with teething, although this is not clear-cut.

As I said earlier, different babies will experience different symptoms and it’s worth bearing in mind that no single symptom can definitively ‘diagnose’ teething.

Many of these beliefs appear to have some root in history as far back as Hippocrates in the 4th century, when teething was thought to be a deadly disease (“dentition difficilis”, Latin for ‘difficult teeth’). Teeth eruption, it was believed, caused a disturbance in the infant’s nervous system, leading to severe systemic upset. This was, again, most probably due to coincidental timing of onset of teeth eruption and an increased likelihood of serious infection, which in those days often led to infant death. Worse still, many of the treatments used for teething right up until the 19th century were actually toxic, such as opiates, lead, mercury salts, bromide and salt.

So while some studies have suggested that teeth eruption is associated with certain physical symptoms, none has really been able to establish causal relationships, and others have found no associations at all. It may be that a diagnosis of teething can relieve parents’ anxieties about an upset infant. Understanding true causal factors, however, is important to prevent misdiagnosis – attributing symptoms to teething could miss more serious conditions that require immediate medical attention.

P.S. I was hampered in my access to a lot of the research in this area, and so if I’ve missed anything then please let me know. A good argument to support Open Access publishing!

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

Spuriouser and spuriouser: the Greenfield effect

Baroness Susan Greenfield, Professor of Pharmacology at University of Oxford, has been in the news a bit recently. She’s being getting a lot of coverage due to her views on the (possible) effects of computer-based activities on children’s mental development. The most striking claims are that the use of social media tools, such as Facebook and Twitter, can lead to autism and/or shortened attention span, and more recently that playing computer games can cause dementia and alter risk-taking behaviours.

These claims have attracted a lot of criticism from bloggers and fellow scientists alike for, amongst other things, being totally unsupported by any peer reviewed research and contradictory to known biological effects. Baroness Greenfield has responded at various points by accusing her detractors of stifling open debate and likening them to those who denied a link between smoking and lung cancer. She also asserts that she’s ‘just asking questions’, which prompted an inventive stream of similarly spurious links on Twitter (#greenfieldism). The serious point behind the humour being that, without any evidence behind, it is just as valid to juxtapose internet use and autism as it is to link Rebecca Black and the Greek sovereign debt (courtesy of @alsothings).

A similar thing happened when Glenn Beck started ‘just asking questions‘, which lead to counter questions about Glenn Beck’s personal history. Although this was an overly extreme question with which to respond, it does highlight the danger of suggesting causal links without any empirical support whatsoever.

Putting unsupported claims in the spotlight to push personal viewpoints about computer games and social media, especially when they’re packaged as scientifically validated ideas, is a dangerous path to lay. The effect of technology use on brain development is clearly an important topic to consider, but any guidance must have some scientific proof behind it. Even a single study that has been through the peer review process and published in an academic journal is not enough to make the sort of bold claims Susan Greenfield has made . Only once hypotheses have been discussed, repeated, followed-up, tested on different groups by other scientists do theories start to become accepted (or rejected) by the scientific community. Baroness Greenfield hasn’t even got as far as the first step.

Tentative evidence can be found to suggest we need to seriously consider the effect of increased computer activity, such as whether violent computer games can alter brain activity and wiring. These types of studies, however, are fraught with potential confounding factors – do violent computer games change the brain activity of gamers or are gamers with particular types of brain activity more drawn to violent computer games? This is why a body of evidence is needed to eliminate these confounding factors and tease out the true causal link.

Parents have a hard enough time in drawing out the best advice, many of which appears to be based on personal opinion and gut-feeling, and so a scientist making raising serious doubts without going through the proper scientific process first can only add to anxiety and confusion. These effects are often long-lasting too. While Andrew Wakefield’s dodgy claims about the link between the MMR vaccine and autism has been thoroughly refuted by the scientific community, culminating in the original research paper being retracted and Dr Wakefield being struck off the General Medical Council register (see this for a brief history), doubts linger in parents’ minds and huge efforts are still being made to bring the vaccination rate up to the required level (e.g.).

Technology now available to children provides unparalleled access to information resources, creative tools and network sharing, and my inclination is that this is A Good Thing for broadening and challenging the mind (see Carmen Gets Around for a similar conclusion). Of course, I await the evidence to support this, but one thing is clear, computer technology has changed the way our kids behave forever. Just watch this YouTube clip…

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