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.

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