Duration of exclusive breastfeeding and risk of anaemia
There's been a lot of stuff in the news today about a paper that's just been published in the BMJ by Mary Fewtrell and colleagues, which questions the current recommendation that infants should be exclusively breastfed for 6 months. There are many issues here, and I don't have time to look at all of them, but one thing that I found interesting is that the paper raises the possibility that exclusive breastfeeding for 6 months may increase the risk of iron-deficiency anaemia in the infant, compared with exclusive breastfeeding for only 4 months.
So what does the evidence show?
The short answer is: not much. A systematic review, last updated in 2006 (bizarrely described as a 2002 paper in Fewtrell et al's paper) found conflicting evidence. A randomised trial from Honduras found some evidence that hinted in the direction that breastfeeding for 6 months might increase the risk of anaemia, but the evidence was weak. There was a statistically significant, but small reduction in haemoglobin levels, but no significant increase in the risk of haemoglobin levels below 110 g/L in infants exclusively breastfed for 6 months, compared with those weaned at 4 months.
In contrast, however, an Italian study found that exclusively breastfed infants had higher haemoglobin concentrations. So the evidence from that review that exclusive breastfeeding increases the risk of anaemia is very weak, particularly in developed countries. It is quite possible that the different nutritional statuses in developed and developing countries mean that trials in one setting are not generalisable to the other.
Anyway, back to Fewtrell et al's paper. They discuss the risk of iron deficiency anaemia further, and and point to a study published since the systematic review (in 2007) by Chantry and colleagues. Fewtrell et al's paper is not a systematic review, and so it's possible that there are other relevant papers that have been published in recent years. I don't know whether they have been or not. I couldn't find any in a 5 minute literature search, but it's quite possible that a more careful search would have revealed something.
Chantry et al's study is described by Fewtrell et al as showing that "US infants exclusively breast fed for six months, versus four to five months, were more likely to develop anaemia and low serum ferritin". They also point out that iron deficiency has "irreversible long term adverse effects on motor, mental, and social development".
Let's take the second point first. The evidence cited for the risk of adverse consequences resulting from iron deficiency was not specific to breastfed infants. To claim that 6 months exclusive breastfeeding causes iron deficiency and iron deficiency causes irreversible developmental problems and therefore that 6 months exclusive breastfeeding causes irreversible developmental problems is a rather weak argument. It would be much more convincing if it were shown that 6 months exclusive breastfeeding causes irreversible developmental problems, but that has not been shown. It is quite possible that infants with iron deficiency as a result of delayed weaning could be very different from infants with iron deficiency due to other causes.
But anyway, how sure are we that 6 months exclusive breastfeeding really does increase the risk of iron deficiency?
Well, after reading Chantry et al's paper, I have to say the answer is "not sure at all". Chantry et al looked at 2 separate cohorts of children, and measured iron deficiency by 3 different measures: low serum ferritin, low haemoglobin, and a history of anaemia. A major weakness of the study is that history of anaemia was based mainly on reports by the parents, with no medical verification. I'm not at all sure how reliable such self-reporting is.
If I were to be convinced that 6 months exclusive breastfeeding increases the risk of iron deficiency, then I would like to see some sort of consistency in the results. However, the results were highly inconsistent. The risk of low haemoglobin was not significantly increased in either cohort after 6 months exclusive breastfeeding. The risk of low serum ferritin was increased in one cohort, and the risk of a history of anaemia was increased in the other cohort. Only 2 significant results out of a possible 6 results does not strike me as convincing. It's also worth noting that although the risk of low haemoglobin was not significantly different between those exclusively breastfed for 6 months and those exclusively breastfed for 4-5 months, the risk of low haemoglobin was significantly higher in those exclusively breastfed for less than 4 months in one cohort.
To cite that paper as evidence that exclusive breastfeeding for 6 months increases the risk of iron deficiency anaemia therefore strikes me as misleading. Now of course it's possible that there may be an increased risk of anaemia, as the evidence is inconclusive, and although we don't have good evidence that there is an increased risk, we also don't have enough evidence to say with certainty that there is no increased risk.
But, of course, there is much good evidence that 6 months exclusive breastfeeding is beneficial on other outcomes. It's probably still wise to recommend breastfeeding for 6 months given that we know there are benefits, and the possibility of harm is at this stage unproven. As Chantry et al concluded in their paper "Full or exclusive breastfeeding for 6 months provides greater protection against both respiratory and gastrointestinal infections than does shorter durations, and should continue to be recommended."
Not surprisingly, the paper has been poorly presented in the media. And if you are a regular reader of this blog, you will know by now that it's important to read the research paper before making up your mind about any health stories reported in the media. But there is a further lesson here. Even the journal article may not give the full story. I found out how weak the evidence was here by going back a stage further and looking at the papers cited in the first paper. Just because something is cited in a journal article as being evidence of something doesn't mean that it's good evidence.
The advice not to introduce solids before 6m applies to both formula and breast-fed babies. However this is not addressed in the study and has not been picked up in any coverage I've seen. This study would have been more helpful if it had chosen to review the evidence for the optimum time to introduce solids and whether this is different for breast and formula-fed babies, and whilst they're at it, those babies who are fed both. It has been really depressing to see the media turn this into a 'debate about breastfeeding' when actually it's a question about when to introduce solids that affects all parents and infants irrespective of whether they are formula or breast-fed. Sadly I have read too many comments today from those who have just read the headlines, not even the news article, let alone the original study, who are interpreting this as meaning bf is a 'bad thing'.
I wonder how long it will be before we see the formula companies focussing their marketing to emphasise the iron content of their products....
Adam - thanks for this valuable analysis, a very important perspective. In Canada I've seen little about this story in the media but if it has been poorly presented in the UK is it fair to call it "dreadful science reporting"? Journalists are not scientists. Their job is to report what the scientists say. If the science is poorly presented by the scientists there's only so much a journalist is qualified to do about it. But I hear you!
[...] #90 Irina R(3) Member Duration of exclusive breastfeeding and risk of anaemia Looks like the media are hyping up what was actually a rather inconclusive piece of research... [...]
Hi Kate
I didn't really go into the way this has been reported in the media in any depth in the blog above, but trust me, it was dreadful. Here is an example. "Breast is not best" is a hugely irresponsible headline, and I'm sure we can all agree it's dreadful. The scientists never said anything of the sort, and the journalists were entirely at fault for reporting such rubbish.
Now, in this case, there is a further complexity, which is that the peer-reviewed paper itself had subtle flaws in it. I suspect what you're arguing here is that journalists couldn't be expected to spot those flaws. Maybe not. But a good journalist should be alert to the possibility that the flaws might be there, and maybe ask a few people who could be expected to know.
I know who to ask now! I did see a good report by Sarah Boseley in the Guardian ( http://www.guardian.co.uk/lifeandstyle/2011/jan/14/six-months-breastfeeding-babies-scientists ) and was particularly impressed that she brought up the issue of industry ties. Not that it completely skews thing, but it's worth noting that the authors of the paper have received consulting fees from baby food and infant formula companies in the past.
Interesting point about the industry ties, Kate. I didn't mention them in my post above because I don't think they're actually that important in assessing the data. The data should stand on their own merits. If the conclusions of the paper are justified by robust data, then the paper is fine. If the conclusions of the paper are based on shaky data, then the paper is questionable. Both those things are true irrespective of any competing financial interests.
However, the industry ties are interesting in that they provide a useful pointer about when it might be worth reading a paper more critically. If a paper concluding that early weaning is beneficial has financial ties to the baby food industry, then to me that is simply a warning sign. Having noticed the warning sign, it then seems worthwhile to look closely at the data to see if the paper stacks up.
A medical analogy seems appropriate. Think of the competing interests as recurrent unexplained tiredness and a biased paper as anaemia. You may or may not have anaemia. You will only know if you have a blood test. You are more likely to have the blood test if you are being investigated for unexplained tiredness. However, the results of the blood test give you a definitive answer, and being tired is no longer relevant.
But, Adam, there *isn't* 'much good evidence that 6 months exclusive breastfeeding is beneficial on other outcomes' - at least, not that it's all that beneficial compared to exclusive breastfeeding for 4 - 5 months followed by breastfeeding plus solids, which is the alternative being suggested by the authors. Have a look at the WHO recommendations that everyone's hyping up so much. The only difference their review found in terms of outcomes for babies was from the PROBIT study by Kramer et al, in which breastfed babies who started mixed feeding or solids between three and six months had a slightly higher rate of gastroenteritis than babies exclusively breastfed for six months. The actual risk of gastroenteritis for the mixed-feeding-after-three-months group was around 1 in 40, and that will include cases caused by mixed feeding between three and four months, which will skew the results further. There's one other study (by the Chantry et al group that also wrote the paper on iron-deficiency anaemia that you're critiquing above) that found a slightly increased risk of chest infections and frequent otitis media in babies who started solids or formula between 4 and 6 months (again, the attributable risk of chest infection was only around 1 in 40 on adjusted figures) but not all the babies in that group were continuing breastfeeding until six months, so, again, that would skew the result.
So, we're looking at some flawed evidence of relatively small benefits. I agree that the evidence for potential harm with delaying solids until six months is currently also pretty poor, but I do wish people would look as searchingly at the other side of the argument instead of simply parroting wholesale the dogma that there's good evidence for keeping babies exclusively breastfed for six months. There's some evidence, but it's really not that great.
Hi Dr Sarah
You make a good point. Although it's true that the evidence for the benefits of breastfeeding in general are compelling, you're quite right that the evidence for the benefits of 6 months exclusive breast feeding in comparison to 4 months exclusive breastfeeding is pretty weak. I guess I was confusing those two issues a bit in my post when talking about the benefits, so thanks for picking me up on it.
I've had a look at those two papers (Kramer et al and Chantry et al), and I agree with you that the evidence for benefits is rather weak. The evidence suffers from similar problems as the evidence of harm, ie not being replicated in other studies, not showing consistently statistically significant results on all outcomes, etc. There is evidence of benefit, of course: reduced gastrointestinal infections in one study and reduced risk of pneumonia and recurrent otitis media in the other study, and to be honest I think it's slightly stronger than the evidence of harm, but I agree it's still far from conclusive.
So I think I agree with you. The evidence for 6 months exclusive breastfeeding versus weaning from 4 months is really pretty weak either way.
Thanks very much for your contribution. It's good to be made to think a bit more about any bits where I may have missed something.
Adam
Thanks for your response! After all the one-sided hype I've been reading, I do appreciate having somebody treat the subject with such even-handedness. ;-) And I was very interested to read your comments on the Chantry et al paper on risk of iron deficiency - I don't have access to that study, so it's good to hear the views of someone impartial who has.
I'm wondering if you would be able to comment on another relevant study? The 13th reference the authors give is to a study done in Germany that may be relevant to this question, but, from the abstract, I can't tell whether the study compared the 'exclusively breastfed for 4 - 6 months' group to the 'exclusively breastfed for 6 months' group. If they did, it would be very good to know the results, plus any obvious flaws/strengths you can see in the study. 'Rebhan B, Kohlhuber M, Schwegler U, Fromme H, Abou-Dakn, Koletzko BV. Breastfeeding duration and exclusivity associated with infants’ health and growth: data from a prospective cohort study in Bavaria, Germany. Acta Paediatr2009;98:974-80'. If you do have any chance to look at it and comment I'd be most grateful. Damn, I miss not having access to a proper library...
The Rebhan et al paper compared 3 groups: exclusively breastfed for at least 6 months, exclusively breastfed for at least 4 but less than 6 months, and with infants breastfed for less than 4 months (or not at all).
It found a significant reduced risk of gastrointestinal infections in the >6 months group, which seemed to be robust in multivariate analyses. However, as with all epidemiological studies, it's hard to know whether they controlled for all relevant confounders in the multivariate analysis, so the results, while encouraging, are far from conclusive. They also relied on self-reports of gastrointestinal infection, and it's possible that some bias was introduced there.
It's one of the pieces of evidence suggesting that 6 months exclusive breastfeeding reduces the risk of gastrointestinal infections. But as we agreed above, that relationship is not conclusively proven.
If we start at the beginning of a new baby's life and delay cutting the cord until all of baby's blood is in his or her body, maybe this would have a bigger impact on iron levels rather than questioning the weaning age and possibly 'blaming' breastfeeding for lower iron levels in children.
Nicola, thanks! That's exactly what I was going to say! I've been reading a lot about physiologic cord clamping this month, and I am convinced that for most healthy, term infants, they need that blood! It is theirs!
And I'm a big advocate of letting the baby show when he/she is ready for solids; some may be 4 months old; some may be 12 mos. old! I've had 3 kids who would.not.take any solid food until close to 10 or 11 months old. Just not.
Nicola & Becky, it does indeed appear that delaying cord clamping can help the baby's iron levels. However, the evidence isn't totally conclusive, so it's yet another of those areas where "more research is needed".
There's a Cochrane review of delayed cord clamping here.