Notwithstanding that epistemic error (and others noted below), the authors of the study actually wrote a fairly modest paper and almost kept their conclusions appropriately tentative. They cannot be blamed for the news frenzy that followed the publication (presumably BMJ, the journal it was published in, or the authors’ university’s publicists deserve that blame, though it is possible that the authors become less accurate when talking to reporters – a lot of them do). Basically the authors observed that, contrary to the official WHO advice, it does not appear that there is any strong argument for women in wealthy countries to exclusively breastfeed (no other food) their babies for 6 months rather than just 4.
The justification for the extra two months is mainly infection risk, which the authors of the new paper found appears to be a bit higher in rich countries, but not much. This contrasts with poor countries where prolonged exclusive breastfeeding is the best defense against foodborne and waterbourne disease, or starvation for that matter. WHO is notorious for making recommendations as if the world were a lot more homogeneous than it really is, and local health officials commit the even less forgivable error of not bothering to figure out when WHO is offering them bad advice. So, the main bottom line was that British women who wanted not to exclusively breastfeed for the extra two months should not feel bad about that, despite Britain adopting the WHO recommendations.
That is about it. If only the authors had simply said “There is no compelling evidence favoring 6 months over 4.” everyone would be a lot happier and better informed.
Indeed, the authors acknowledge that they are working with evidence that is inadequate for saying much more:
Yet infants exclusively breast fed for 6 months represent, globally, a small, potentially biased subgroup (for example, under 1% of UK infants in the 2005 UK Infant Feeding Survey [reference note]), that presumably excludes those perceived by their parents as signalling [sic] hunger and so requiring weaning foods earlier. Generalisation from this subgroup must therefore be questioned.
So they recognize that we do not really have much data on 6 versus 4 – enough to detect a big difference but not a small one. Well, maybe they recognize that. They do not say it, and what they actually say is wrong: If many babies apparently need supplemental feeding before 6 months, or the mothers otherwise bail on exclusive breastfeeding despite the current recommendations, then this advice does not apply to them (other than to perhaps say “do not sweat it so much”). The question is what to tell those who think that going the full 6 months – is it worth the extra effort, or is it even a good idea.
This is another case of researchers knowing just enough epidemiology to be dangerous. They understood the concept that it is possible to have data from a subgroup that is unrepresentative of the whole population. But apparently they only remember being told that this is a bad thing. The missed the detail that this is a bad thing only if you want to extrapolate to the entire population. If you actually want to study that subgroup, then it works out quite nicely. In this case, it is obviously that subgroup that is of interest. Mothers who were not going to exclusively breastfeed for 6 months anyway do not need to be advised to consider not doing so.
It never fails to amaze me how often epidemiologic analyses draw conclusions based on rules of thumb that clearly do not apply to the particular case.
As for affirmative reasons to introduce other foods before 6 months, the authors went on to suggest that there are a couple of reasons. A single study that they found suggested that the extra two months have a huge effect on whether babies suffer from serious iron deficiency. This result seemed rather incredible, an increase in the risk from about 2% to about 10%, particularly because there was no suggestion that this result had ever been replicated despite the fact that it is (a) huge, (b) important for people to know, assuming it is really true, and (c) relatively easy to check in any number of ways. This strongly suggests that this is a classic case of “our study is the first to show…” calling for the conclusion “…and therefore it is almost certainly wrong.” That study was based on mining a general health survey, which in itself is not necessarily a problem, but given how many dedicated breastfeeding studies there are, we would not expect something real to show up there that was missed everywhere else. I cannot report much more about it, though, because I could not get a copy (who knew that something published in the journal “Breastfeeding Medicine” would be so difficult to get a copy of; after all, there must be dozens of libraries that subscribe to it – a perfect case of “publication” as score-keeping rather than actual communication of information). Thus, it seems like a big mistake to have taken this claim seriously.
The second argument against longer exclusive breastfeeding was rather more convincing, being based on several studies. Some research has found that failing to introduce gluten (grain protein) before 6 months increases the risk of celiac disease (an inability to eat gluten due to an autoimmune reaction), which is quite a problem given our grain-centric diets. Assuming we take this caution seriously, the advice from the new study really should have been not just, “There is no compelling evidence favoring 6 months” but also “and it is probably a good idea to introduce some grain, if nothing else, before 6 months”. A careful reading of the paper (if you skip over the faith in the one study that claims a huge risk of iron deficiency) shows that the authors basically report this.
So what went wrong? Why did this cause headlines, fearful reports on the television news, and substantial consternation? Because it was reported as if it were some radical change in advice. That is, the naive WHO advice had been touted by naive British officials as if it were definitive and precise, and represented a huge variation in health risk, when actually it was tentative and as far as anyone could tell, whichever way was best was only slightly better. And the vague suggestions from the new review were presented the same way. (And why did American reporters make a big deal about it? Apparently because they did not even stop to notice that the “new” advice conforms to what is typically advised in the US, notwithstanding the random assertions of the Surgeon General today.) While it is gratifying that reporters and their readers have so much faith in epidemiology, it might be useful to realize it is much fuzzier around the edges than typically portrayed.
At least there is some good news. Since we cannot be sure whether it is better for someone to believe the “old standard” or the “new advice”, and any difference is small, then whatever people took away from the news frenzy makes little difference. The bad news is that while some reports touted this as imperative advice, a few recognized the fuzzy edges and did not go overboard with their conclusions, and most were in between, I do not recall seeing a single report that mentioned their one interesting conclusion: that introducing gluten in the fourth or fifth month dramatically lowers celiac disease risk.
That, I think, was the fault of the researchers and their publicists. Reporters often bury the lead, but if they had been told that this was the main important piece of advice, I suspect they would have run with it. It is a perfect story: “And coming up after the break, the simple food that could save your baby from a lifetime of misery. Stay tuned.” It is sad to see the hype masters let us down so badly.
On the other hand, I am not sure how good the evidence is about celiac disease, but I intended to find out in the next 2-3 months and will probably find it blog worthy, so stay tuned.