By the time you read this, many of you are probably already in panic mode.
The news outlets are probably heralding the news of a NEW study, PROVING that breastfeeding reduces a child’s risk of leukemia, or the unfortunate corollary, that formula feeding raises a child’s risk of developing this cancer.
Take a deep breath. This “study” is actually a meta-study. Meta-studies are often considered the highest level of research, since they are synthesizing data and ruling out certain study findings based on quality criteria, thus weeding out the “bad” studies and only showing us the ones with results worth caring about. They are very useful, because one study alone doesn’t tell us much; many high-quality studies, when looked at together, can give us a much better feel for what the reality of the research actually is.
But the same thing that makes meta-studies so useful can also be their fatal flaw. If the body of research they are considering “quality” is not actually that high-quality at all, then the results they get are far less impressive. As Joan Wolf has suggested, if you do the use the same poorly-designed study protocol one hundred times, you may very well get the same result. But that result comes from poor design.
That’s basically what’s going on in this study, Breastfeeding and Childhood Leukemia Incidence: A Meta-analysis and Systematic Review. Despite numerous references to controlling for “quality” in the studies they chose, there is no discussion of which confounding factors were controlled for in any of these studies:
Selection criteria for the present meta-analysis included articles researching the association between breastfeeding and childhood leukemia… Studies had to be case control for the purpose of the statistical analysis; have breastfeeding as a measured exposure and leukemia as a measured outcome; include data on breastfeeding duration in months, including but not limited to, 6 months or more (where relevant data were unavailable in the publication, the authors of the studies were contacted); and been published in peer-reviewed journals with full text available in English. Two investigators… independently searched the literature, reviewed and assessed the articles, and decided on inclusion. We identified 25 case control studies examining the relationship between breastfeeding and childhood leukemia risk, 7 of them were not included in any previous meta-analysis.
I looked up most of the studies they referenced, and they were pretty similar to the general quality of infant feeding studies (in other words, lacking a lot of necessary and relevant controls). And sometimes, it wasn’t even the study authors’ faults – because the design of the study didn’t really allow for much control, or because they just didn’t focus that closely on breastfeeding. For example, one study they referenced as “high quality” had “never breastfed” as one of many factors they examined for correlation to leukemia. And yes, “never breastfed” had a moderately higher rate of leukemia- but so did “having eczema”.
On a positive note, since the study did not/could not control for exclusive breastfeeding, but rather just “breastfeeding to six months”, this might mean that the benefit could be conferred even for supplementing or combo-feeding moms, which is a type of breastfeeding more women are finding it possible to do. That also suggests, to me, that more research needs to be done into the mechanisms behind this benefit – for example, did they control for the type of formula used? Is it something in the formula, or simply something that the formula is lacking? Did they control for the reasons the babies stopped breastfeeding in the first place? Could introduction of solid foods have something to do with it (the six month aspect is intriguing – why not a great benefit at 4 months? 5 months? What is so important about that 6 month mark)?
It would be far more interesting and newsworthy to see a metastudy which really controlled for confounders – one that only used studies which did their due diligence in controlling for everything that can screw up infant feeding research, and discussed how they went about this.
And something else: remember the outrage when an interviewee on this blog hypothesized that there might be a association between insufficient feeding/brain injury in the neonatal period and autism? The consensus was that it was premature to even speak of a possible association – to even put the idea out there – which I fully understand (again, those were the physician’s views, not mine – I do not have a sufficient understanding of this particular body of research to even converse intelligently about it). Yet, some of the same people who have run this physician over the rails for merely suggesting her hypothesis, are the first to jump on the not-breastfeeding-causes-cancer bandwagon. And that’s just hypocritical, because you can’t be raging about scaring parents unnecessarily, and then in the same breath, scaring parents unnecessarily. Until we have a figured out exactly how breastfeeding until 6 months may prevent leukemia, there is simply no reason to believe it’s anything more than an association.
This science isn’t my biggest concern with this one, however (mostly because there was no science involved in this particular study – just an analysis of other people’s science). I’m far more interested in how the authors jump to the conclusion that breastfeeding is a “highly accessible, low-cost public health measure”, as quoted below:
The meta-analysis of all 18 studies indicated that compared with no or shorter breastfeeding, any breastfeeding for 6 months or longer was associated with a 19% lower risk for childhood leukemia (odds ratio, 0.81; 95% CI, 0.73-0.89). A separate meta-analysis of 15 studies indicated that ever breastfed compared with never breastfed was associated with an 11% lower risk for childhood leukemia (odds ratio, 0.89; 95% CI, 0.84-0.94), although the definition of never breastfed differed between studies. All meta-analyses of subgroups of the 18 studies showed similar associations. Based on current meta-analyses results, 14% to 19% of all childhood leukemia cases may be prevented by breastfeeding for 6 months or more.
CONCLUSIONS AND RELEVANCE
Breastfeeding is a highly accessible, low-cost public health measure. This meta-analysis that included studies not featured in previous meta-analyses on the subject indicates that promoting breastfeeding for 6 months or more may help lower childhood leukemia incidence, in addition to its other health benefits for children and mothers.
“Highly accessible” is not exactly an accurate representation. As I said to reporter Tara Haelle for Forbes.com, “Women have clearly gotten the message that “breast is best” – in fact, reduction of leukemia risk is one of the benefits public health posters like to emphasize, as it packs an emotional punch. This is not “new” news.” And if women weren’t finding it easy of possible to breastfeed for 6 months before, despite being freaked out that their kids might get cancer because of it, this reiteration of old news isn’t going to change that.
I actually think it would be amazing if they did discover some factor in breastmilk that could reduce cancer. It’s certainly plausible; we’ve already seen evidence of cancer-fighting properties in breastmilk, via lab studies. But our goal should be isolating that factor in a way that we might recreate it, or at least mitigate the risks to babies who cannot receive their mother’s milk, rather than using it as a motivating factor for breastfeeding promotion.
Why? Because there always have been, and always will be, children who cannot or will not get breastmilk from their mother for 6 months. We have always needed and desired alternatives. If we can focus on finding out why there is an association between breastfeeding and leukemia risk (and again- take a breath, because there have also been studies that showed no significant correlation between the two, so it’s certainly not an open and shut case), maybe we can mitigate that risk for those who are not breastfeeding. Now that would be something worthy of some juicy headlines.