Tag Archives: Breastfeeding

Four ways breast milk is really interesting

You might have heard a lot that breastfeeding may reduce the risk of infections, allergies and gut problems. But it’s perhaps even more fascinating than you realise.

1. Mums may produce different breast milk for sons and daughters

Dr Katie Hinde from Harvard University studies lactation in monkeys to understand how breast milk provides not only nutrition, but shapes immunity, nervous systems and behaviours in their offspring.

Her team has found that even a monkey mother’s own breast milk can vary in the composition of fat, hormones, protein and minerals. It can depend on her age, how many children she’s had and what she’s been eating now and in the past. But, as this Naked Scientists interview explains, it even matters whether she’s had a son or a daughter.

Rhesus macaque monkeys produce more, lower energy milk for daughters, but less, higher energy milk for sons, in such a way that the overall energy supplied balances out. Why this is is unclear and Dr Hinde’s team is working to unpick these tricky questions. The monkey mothers also produce more calcium for daughters, which Dr Hinde speculates is linked to a quicker development of daughters’ skeletons.

As the interviewer, Kate Lamble asks, how do the monkey mums know whether it’s a son or daughter? Dr Hinde thinks it’s probably down to more hormones produced during female foetal development affecting mammary glands. It could also be behavioural interactions between mother and offspring after birth.

The big question is, does this hold true for humans? Is this something that mattered more in our evolutionary past, but is less relevant in our cosier modern world?

2. Time of day matters

Many animals exhibit day-night rhythms that can affect everything from sleep-wake cycles, metabolism, immune responses and heart rate. And it seems breast milk production is no different.

Milk produced during the night contains higher levels of a hormone, melatonin, which is known to regulate day-night (“circadian”) cycles. Researchers have suggested this can help reduce irritability and prolong night-time sleep, but more work is needed to show this for sure. Adults can manufacture melatonin from essential molecules taken in through the diet, but babies can’t.

Other studies have focused on tryptophan – an important building block in the body’s biochemical manufacturing of melatonin. One study linked higher levels of tryptophan in breast milk at night with a rise in melatonin in the breast-fed babies, which was also associated with more sleep.

To try to establish whether elevated tryptophan caused improved sleep (rather than because of some other differences between breast- and formula-fed babies), another study compared babies who were fed formula milk with added tryptophan at night, added tryptophan in the day and with no added tryptophan at all. Only babies fed added tryptophan at night had better sleep and metabolites in the urine suggested this was down to the production of more melatonin.

Whilst the overall effect on babies’ sleep and whether fluctuations in the makeup of breast milk can really cause changes is still to be fully teased out, these findings suggest that mothers who express milk for their babies for a later time may want to pay attention to what time of the day they did it.

3. Hormones in breast milk can affect behaviour too

Hormone levels, such as cortisol, can naturally fluctuate throughout the day. Cortisol, in particular, is not only important in the stress response but is needed in the mammary glands to stimulate new milk production and protect the survival of mammary cells.

Researchers comparing breast- and formula-fed babies have suggested that higher cortisol levels in milk are associated with more fearful babies. Others studying monkeys and humans have reported levels of maternal cortisol affecting temperament in three-month olds, and this may differ for sons and daughters. For some animals, like red squirrels, it may give them a competitive advantage – cortisol-like hormone levels rise as a forest gets more crowded, which accelerates the growth of their offspring.

Back to Katie Hinde’s research. Again, studying rhesus macaques, her team wanted to know whether these effects were genuinely down to cortisol or because of variations in the amount of nutrients passed on (which are in turn affected by hormone levels). The researchers measured milk one month after birth, and again three to four months after birth. Generally, higher levels of cortisol in milk were associated with babies who scored higher for nervousness and lower for confidence.

But why? They point to evidence that elevated cortisol in humans may lead to reduced growth, and speculate that there may be a trade-off between infant temperament and growth – if more nervous, less confident behaviours reduce activity, then the available energy from milk can be put towards growth, particularly for sons. This may be particularly crucial in times when resources are scarce or competition is high.

At least in rodents, the receptors for these hormones are most abundant in the gut in infancy, before declining into adulthood. This suggests that babies of at least some animals may be taking an active role in sensing the environment through their mother’s milk.

 

4. Breast milk may shape the friendly gut bacteria

Californian researchers compared the bacteria in the intestines of breast- and bottle-fed baby macaque monkeys between five and 12 months old. They also took blood samples to analyse the immune cells in the growing babies.

The bacteria profiles in each group showed stark differences. The breast-fed babies contained higher levels of Prevotella, Ruminococcus and Lactobacillus, whilst the bottle-fed babies had higher levels of Clostridium. The immune systems of the two groups also differed. Breast-fed babies had more immune ‘memory cells’ and ‘helper cells’ (which help fight off foreign invaders) and produced a sturdier immune response when isolated blood cells were challenged. The researchers noticed differences in chemical signals in the blood known to influence how the immune system develops.

Another study, this time on mice, may give clues as to one way this can happen. By manipulating particular antibodies in maternal milk, these researchers showed that a lack of antibodies produced very different bacterial gut colonies and affected how well the mice could cope with an intestinal insult. Both studies showed that variations in bacterial profiles were still seen many months after the experimental diets ended, indicating that the effects on the immune system may be very long-lasting.

All this suggests that breast milk, possibly through the action of antibodies, causes certain helpful microbes to colonise the gut. These then produce a spectrum of chemicals that help shape the maturing immune system, making it better equipped to fend off infections and less likely to trigger allergic reactions.

The question is, for humans in today’s world, how much would these variations actually matter?

 

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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

Milking the (cash) cow?

Or, should I feed my one year old cow’s milk or infant formula?

The Skeptical Son is about to hit one year of age, which brings a few landmarks with it. MMR vaccination, standing up (albeit a little precariously), and a move from specialised (breast or infant formula) milk to regular, unmodified cow’s milk.

This latter point seemed pretty uncontroversial. The UK National Health Service and the American Academy of Pediatrics both recommend feeding cow’s milk to a baby beyond 12 months. The NHS explicitly states: “Infant formula, follow-on formula or growing-up milks are not needed once you baby is 12 months old”.

So I was intrigued to see infant milk formula products specifically targeted at the over one year olds, such as Aptamil 1+yr & 2+yrCow & Gate 1-2yr & 2-3yrHipp Organic growing up milk (from 12 months), and SMA 1-3yrs.

A look at the scientific literature, in line with the NHS and AAP guidance, backs up a move to cow’s milk at 12 months. Unmodified cow’s milk is not recommended before this age because it contains high levels of sodium, potassium, phosphorus, and calcium, and lacks vital nutrients, such as iron, vitamin C, and linoleic acid. As a baby’s diet becomes more varied and complex by the age of one, many of the nutrients previously gained from milk (breast or modified cow’s formula) is obtained from food. An infant can, in most cases, safely move to consuming cow’s milk, and it is only if a specific deficiency develops that they will need targeted supplementation.

http://www.flickr.com/photos/jelles/2902422030/

Cow by JelleS [CC-BY-2.0]

The NHS’s health information leaflet, however, says: “It is recommended that all babies aged from six months to 5 years are given a supplement that contains vitamins A, C and D, unless they are drinking 500ml (a pint) of infant formula a day (infant formula has vitamins added to it)”. This then brings us back to enriched infant formula.

The infant formula manufacturers appear obliged to acknowledge that breast milk is recommended for young babies (see disclaimer notice*), consistent with the World Health Organization’s guidance. All of them, though, promote their 1 year+ products as, variously, enriched with iron, vitamins C & D, GOS/FOS prebiotics and omega fatty acids. Advertising claims include milk formula that is “nutritionally superior” to cow’s milk, “has been specially developed to help meet the nutritional needs of toddlers”, and will “encourage your toddler’s natural friendly bacteria to thrive”.

So now I’m a little torn. Anaemia, avitaminosis and lactose intolerance are, evidently, serious conditions that need to be addressed, and products need to exist for these cases. But the marketing doesn’t seem in line with the healthcare advice: without looking into it, I was initially left with the impression that the specialised infant formulas represent the gold standard, containing everything that is needed to support my son’s “amazing development” [© Cow & Gate]. The adverts and packaging don’t suggest these products are for cases where a deficiency has been identified, rather it appears to play to the ‘don’t take any chances’ or ‘be on the safe side’ worry of parents. SMA, for instance, says “it is hard to know if they are getting all of the right nutrients they need at this important time”.

I guess this speaks to a wider problem with nutritional supplements, ‘superfoods’ and enriched dietary products, some of which make all manner of claims about health and well-being (see Andy Lewis’ Quackometer for more ‘Confusopoly of Diet’).

Anyway, now for a quick look at money, something that’s precious to many families. A 900g tub of Aptamil 1+ yr costs £8.49 (Sainsbury’s price). This means that a daily intake of 500ml will cost 79p (83.3g formula). An equivalent daily portion of whole cow’s milk costs 26p. Even adding in a multivitamin supplement works out at an extra 13p a day. Over a week this difference amounts to £2.80; over a year it’s a saving of around £145.

I should emphasise that the post-one year milk formulas seem completely legitimate products to sell and I’m far from claiming a conspiracy, but I explore it here simply to question whether their advertising is a little misleading. Of course, dietary products claiming all sorts of health benefits is not a new or isolated phenomenon, but I worry that the baby market particularly plays on the anxiety of parents that inclines them to prove themselves as perfect guardians.

Maybe I’m being overly cynical in suspecting that the manufacturers are being unreasonably opaque. Perhaps I’m too naïve in wishing that promotion of products that affect ours and our babies’ health was more honest. Would it be regulatory overkill to make infant formula products, in the same way as the breastfeeding disclaimer, carry an objective notice about cow’s milk and the current healthcare advice?

And on that ambivalent note, I shall end.

*The common wording across manufacturers’ websites and the prominent positioning of the statement (it is displayed any time one tries to click through to a product for the first time) suggests this is a statutory requirement. This would be interesting if it is, so any light that anyone can shed on this would be appreciated!

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.

Where are the facts?

This was the demand from a very pleasant woman we met on a train a couple of weeks ago. She had been enquiring as to how our son, now 6 months old, was getting on with his sleeping and weaning. Not great on either count, since you ask.

She was, however, slightly taken aback that current medical advice is to start weaning at 6 months, rather than at 3-4 months as she was advised when she was raising her babies (30-40 years ago, at a guess). She was also a little dismayed that babies are now overwhelmingly placed on their backs to sleep, instead of on their front.

So, “where are the facts?”

Well, science doesn’t really work like this and scientists don’t deal with immutable facts. Research is conducted, evidence is gathered, and conclusions are drawn. And the cycle is repeated over and over and over again. Sometimes, the new evidence backs up the previous conclusions and those ideas become strengthened. Sometimes, however, the new evidence doesn’t match the previous conclusions, and so thinking may change. As such, scientists should always be prepared to change or modify their positions as new stronger, evidence emerges. In the case of babies sleeping on their backs, an accumulation of evidence over many years that showed a reduced risk of cot death that led to the change in received wisdom.

There are also different strengths of evidence and there some types of studies in which we can more confidence. A study that takes a part of a population, randomly splits them into test and control groups before monitoring the effects of a treatment versus control has far more power than a study that looks back in time at a population and tries to work out why some groups are different. Because of this, a new study, using a more reliable method may be carried out that modifies experts’ views. This is especially relevant for pregnancy and child development, as it’s hard to perform randomised controlled trials (the first type of study I mentioned above) with pregnant women and children, because parents are generally less likely to enter into anything they perceive as potentially risky.

In the case of weaning at 6 months, one only has to look at the expert review that forms the basis of WHO’s current advice to see that we aren’t dealing with cast-iron ‘facts’.

The experts concluded that 6-month exclusive (or predominant) breastfeeding is required to provide the right nutritional balance and to protect against gastrointestinal infection. After 6 months, solids should be introduced in order to meet a baby’s additional energy and nutritional requirements. There are even apparent benefits to the mother from exclusively breastfeeding for 6 months rather than 4 – mothers showed greater weight loss (if this is indeed desirable) and had a longer post-natal infertility period. It wasn’t cut-and-dried, though, as care must be taken to avoid iron deficiency in babies exclusively breastfed for 6 months, as well as special care in developing countries to ensure that babies are not malnourished as a result of poor maternal nutrition.

But, there are a few cautionary tales to add to this. First, there wasn’t a huge number of studies that looked at the health status of babies who had been exclusively breastfed for different periods to compare. Second, some of the studies that were included looked at a relatively small population of babies. Third, the studies differed in their quality and potential for bias, such as whether it was observational or whether it relied on self-reporting. Fourth, some studies didn’t show a difference in health status – is this because no effect was present, because the study design was weak, or because they hadn’t studied enough babies to show an effect? We don’t know.

This is not to undermine the advice of WHO and other health agencies – it is advice we’ve followed for our son – it just highlights how health advice is often formed and how it can be subject to change.

The potential for scientific judgement to be swayed over time also means scientists are generally more cautious and moderate than perhaps people expect or, indeed, want. It seems common for people to desire clear-cut and, above all, ‘correct’, advice. This is often reflected in sensational newspaper headlines that overstate tentative research findings, which is unhelpful in informing the public as to the true nature of the findings, as well as to the scientific process itself (see the BBC’s “Spoon feeding ‘makes babies fatter‘” versus this more reasoned analysis from NHS Choices).

This can, unfortunately, sometimes be used as a stick with which to beat scientists: “people were wrong about babies sleeping on their front, so how do you know you’re right now?” A temptingly persuasive argument to ignore those boffins, especially if they’re telling you things you don’t want to hear. But scientists (honest ones, at least) are always working from a position that is based on the best available evidence. If you reject this best available evidence, then you’re working from an even weaker position.

In the case of WHO’s advice on when to introduce solids, it made its judgement because all the evidence, despite some weaknesses, was pointing in that direction. So even though there is more research to be done – the report even acknowledges this and makes recommendations for new studies that should be carried out – it would be unwise to act against what the best available evidence is telling us. And it wouldn’t take a single study to come along to turn that around, it would take an accumulation of solid evidence that showed an opposite and consistent trend.

I didn’t quite manage to finish telling this to the lady on the train, though.

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