STATS ARTICLES 2006
What Science Really Says About the Benefits of Breast-Feeding
June 20, 2006
Dr. Rebecca Goldin
Director of Research, Statistical Assessment Service,Assistant Professor, Mathematical Sciences, George Mason University
Dr. Emer Smyth
Assistant Professor of Pharmacology at Univ. of Pennsylvania)
Dr. Andrea Foulkes
Assistant Professor of Biostatistics at Univ. of Massachusetts, Amherst
The Science Times section of the New York Times announced today that it had received more than 100 letters “pro and con” over its article “Breast-Feed or Else.” Coverage of the reaction suggests that this is a controversial topic, with the Times acting as an honest broker; but when a newspaper compared cigarette smoking to using infant formula, we suspected that there’s got to be something screwy with the science, which is, in fact, the case. By failing to take a thorough, critical look at the evidence for this new public health campaign, the Times has caused needless anguish to countless mothers.
The New York Times shocked women last week with an astonishing article in its “Science Times section” titled, “Breast-feed or Else.” While laying claim to a balanced approach by describing as “controversial” a public health campaign that compares the failure to breast feed as equivalent to smoking while pregnant,” the paper, nevertheless, ended up producing an extremely biased article. In claiming positive outcomes to breast feeding that are unjustified by scientific studies, the Times effectively told parents that giving their babies formula is tantamount to letting them smoke.
But the costs of nursing are substantial: the reduced time for work due to the need to pump, nurse, eat and sleep has a huge economic and social impact on women and their families. Nursing can also lead to depression or other unhealthy emotional states. It can be painful, and there are sometimes medical reasons why nursing is not recommended. Human cytomegalovirus (HCMV) infections can be transmitted by breast milk and can cause considerable problems in newborn babies - and sometimes lead to life-threatening illnesses. Drug addicts obviously should not nurse; but even smokers and drinkers ought to consider the impact (and quantity) of their use on their babies.
And for some women the milk simply isn’t there despite conscientious efforts. This can lead to either health problems for the baby who isn’t getting enough calories, or paying $4-$10 per ounce for donated milk (if it’s available). For a five-month old baby downing about 30 ounces a day, that’s one pretty little college fund gone in human milk.
For these reasons, many scientists have investigated the purported benefits of human breast milk for infants (largely ignoring the mother in their calculations), and the results are mixed. Only in a narrow segment of the population is nursing actually a bad idea, but the real question is how good is good? Can we quantify the extra benefit? Is nursing really so much better than formula that we can make a similar comparison to the risk of smoking and not smoking?
In affirming this comparison, the Times extensively quoted Dr. Lawrence Gartner, chairman of the breast-feeding section of the American Academy of Pediatrics (AAP). Gartner claimed that breast-feeding protects “against acute infectious diseases — including meningitis, upper and lower respiratory infections, pneumonia, bowel infections, diarrhea and ear infections.” The Times added that the AAP claims “Some studies also suggest that breast-fed babies are at lower risk for sudden infant death syndrome and serious chronic diseases later in life, including asthma, diabetes, leukemia and some forms of lymphoma.”
In the AAP primary scientific position statement (hosted on the front page of their breastfeeding page), the organization states “Extensive research using improved epidemiologic methods and modern laboratory techniques documents diverse and compelling advantages for infants, mothers, families, and society from breastfeeding and use of human milk for infant feeding. These advantages include health, nutritional, immunologic, developmental, psychologic, social, economic, and environmental benefits.”
We decided to take a closer look at these claims than the Times did; the real story is both surprising and reassuring.
Nursing and infant death
We start with the scariest question first: Will babies die if they are not nursed? According to the American Academy of Pediatrics (AAP), breastfeeding leads to a 21 percent decrease in the death rate of babies in an age range over one month and under one-year old.
But turn to the AAP’s source. The scientific study used to support this claim found that babies who are nursed are less likely to die… of injuries!
While it may be hard to explain away that data, it is hard to believe that the AAP is recommending that exhausted, tired, guilt-ridden, and otherwise strung out mothers nurse because otherwise, their child might end up falling off a table.
There is, in this paper, a weak association between nursing and a reduced risk for Sudden Infant Death Syndrome (SIDS). But the association is not statistically significant (the 95 percent confidence interval is .67-1.05). And since there is no obvious mechanism for this either, we are left wondering whether this is because breast milk (possibly in a bottle) helps reduce the risk, or whether it’s the physical attention obtained by being nursed frequently during the night, or whether it’s that nursing babies are sleeping with their parent more. If it’s the latter, for example, then we should advocate co-sleeping rather than nursing.
Finding this kind of poor science behind a huge AAP campaign to promote breast milk and nursing over formula got us wondering. What other wives tales are out there?
Nursing and infection rates
Let’s be honest: if the only adverse consequence of not nursing is that babies get a few more colds, we could leave the decision making to the parents. The real question is whether there are dangerous or potentially long-term damaging illnesses (such as ear infections that lead to hearing loss) for babies who aren’t nursed versus babies who are. And how long (or how much) should a baby be nursed in order to keep his or her risk down?
One of the big problems in trying to assess this question is that not all nursing is equal. There are mothers who nurse exclusively, mothers who use expressed breast milk (delivered in bottles), mothers who freeze milk, or use pasteurized (donated) milk, or use some breast milk and some formula, and a combination of all of the above.
Then there are the babies, some of whom are premature, or have low birth weight, or have other health issues that could make nursing harder; there are some babies who are nursed until they are four-years old, and others who nurse until they are six-weeks old.
Finally, we must add a complicating factor that it’s virtually impossible to carry out the gold standard of research on this issue – a randomized controlled study in which mothers are randomly assigned whether to nurse or not. Our observational power may also be limited; at least in principle, because women (and families) who nurse are not the same as those who don’t, making any comparison of the outcomes extremely difficult.
But even if we accept these difficulties and try to assess the literature, the picture is not as clear as that painted by the AAP. We found several incidents, like the death-by-injury statistic, which suggested the organization was exaggerating the findings in the literature.
Many of the papers referenced were done in the 1980s, when medical care, daycare, and social contexts were significantly different from those today. Perhaps more importantly, studies done in the 1980s did not control for all the factors (such as whether the parents smoke) that we now know have an important impact on infant health. Other studies – especially more recent papers - simply didn’t find what AAP claimed they did.
Let’s take the article “ Differences in morbidity between breast-fed and formula-fed infants,” published in 1995 by the Journal of Pediatrics. This article tried to assess the health impact, if any, for affluent families in the United States. These were highly-educated families with access to medical care. The authors compared those babies who were breast fed almost exclusively (no more than 120 ml of formula per day until 12-months old) with those who used formula almost exclusively (defined as having never been nursed, or stopped nursing before three-months old).
In this article, the researchers found that “There were no significant differences in rates of respiratory illness,” which contradicts the AAP’s claim that there were decreased upper and lower-respiratory illnesses for nursed babies. The article adds that “Morbidity rates did not differ significantly between groups in the second year of life.” So whatever protective effects nursing has don’t seem to prevent illness in Year Two.
The researchers, however, did find some health benefits.
Ear infections were down 19 percent among breast-fed babies. The length the infections lasted also diminished, and recurrent ear infections were down by 80 percent. (Interestingly, a different study found a similar effect provided by nursing for four months, making the benefit of longer nursing unclear.)
Diarrhea (defined as two loose stools in a day) was also down among breast-feeders by about 50 percent. So why didn’t the Times article tout the benefits of nursing for these particular health issues? Perhaps it doesn’t churn out the guilt factor in the same way.
Luckily, in none of these cases was there any long-term affects. Over the course of the study, the same number of breast-feeders and formula-feeders were hospitalized, all for pneumonia.
For less affluent families, there may be a greater difference, in large part due to access to medical care or education. However, it seems unfair to assign nursing as the culprit, when our health care system might be a better suspect.
Economic, social and psychological issues
The AAP is not officially in the business of making economic calculations, but that didn’t stop it. The organization touted the potential savings in annual health care costs, decreased costs in public health campaigns, decreased parental absenteeism, and associated loss of income due to taking care of sick babies (presumably, with ear infections), and even the savings on the formula itself – both to the family (at least $400 per year of savings) and to the country (the need to transport formula).
The AAP acknowledge that some of these benefits might be offset by longer doctor-office visits (in order to help women nurse), the costs of pumps and equipment, which the organization cavalierly says “should be covered” by insurance. (That’s consoling.) The AAP also claims that nursing provides “more time for attention to siblings and other family matters.”
The absurdity of these calculations is impressive. While absenteeism has a financial cost, not holding a job has an even larger one – and nursing exclusively for six months typically means that the mother cannot hold down a full-time job. Women need to sleep more, eat more, and find the time to nurse or pump. While parenting and working can be brutal, adding nursing to the list is five hours a day that women just don’t have. With only twelve weeks of leave guaranteed by the government – and that leave is unpaid – few women who intend to work can maintain a commitment to breastfeeding. And even the most religious breast-feeders would be loathe to say they have more time for the rest of the family when they are required to devote so much time and energy to the infant.
These kinds of arguments are simply bad (social) science, and are fed by conviction or opportunism rather than hard evidence. Even worse, it makes one suspect that scientific studies are biased by well-intentioned but possibly misguided doctors predisposed to nursing.
The Times takes the concept that an indictment is as good as a conviction to new heights. It makes such claims as breast-fed babies “appear to be at a lower risk for autoimmune diseases like… juvenile diabetes.” And yet it turns out that this question is only now being asked in a large multinational study. So, in fact, no benefit has hitherto been shown.
Of the studies cited by the AAP as indicating a benefit in this area, one was based on babies in Chile, another on Indians in Peru, and a third only found results for children exposed to food. Infant formula wasn’t even considered!
Added to the failure to examine the AAP’s claims, the Times only reports arguments against breast feeding that stem from how the mothers might feel guilty for not nursing (assuming we accept that nursing is better than formula). There doesn’t seem to be any other possible reason for using formula.
But of course, as anyone who has had to make the decision about whether to nurse or not knows, there are many reasons to want to know if nursing is truly better, or if this is just a throw back public health campaign based on voodoo science.
What to take away from this
Suppose breast-feeding is better than formula – and it seems it is for certain kinds of low-risk infections. How do we put the breast-milk versus formula question into the context of other health choices we make? We make decisions all the time that incur risks but also have benefits for the individual. We get into cars, risking death and injury; we send our kids to school, risking infections; and we eat foods like hamburgers, risking an assortment of problems, from obesity to E. coli. How does the breast-milk versus formula divide fit in to all these risk calculations?
The analogy between not nursing after giving birth and smoking before birth strikes us as pure scare-mongering. Cigarettes contain two substances widely recognized as harmful to babies before birth: carbon monoxide, which leads to decreased oxygen flow (contributing to brain damage or miscarriage) and nicotine, which reduces uterine and placenta blood flow (contributing to a host of placental problems, as well as increased miscarriage).
Cigarette smoking is associated with low birth weight (and its concomitant health problems), as well as increased perinatal mortality (the death of a late-term fetus or baby under one-week old). Smoking has also been associated with cognitive development problems as well as an assortment of childhood cancers. It is also a predictor for SIDS. For a summary of some of the literature on cigarette smoking and pregnancy, read this.
Thus we come to the inescapable conclusion: Formula is nothing like cigarette smoking; and it is nothing short of irresponsible for a public health policy campaign to make this comparison.
We found that a lot of those who advocate breast-feeding are relying on voodoo science; it may not have a harmful affect for most women, but it could negatively impact those who would otherwise prefer not to nurse for an assortment of reasons.
As for the risks, we’ve detailed them as best we could. Remember that driving in a car carries a risk of death of 1 in 6,745 per year (according to the Harvard Center for Risk Analysis). Even waiting to have a baby increases the chances for breast cancer (should we put a warning label on condoms saying "avoiding pregnancy can increase your risk of breast cancer"?). Our lives are filled with risks, small and large. Not nursing is a small risk, the real question is what it costs (or benefits) you.
This article generated an enormous and spirited response. We will add the most interesting of these responses below - editor
from Catherine Sullivan, MPH, RD, LDN, IBCLC
Perhaps the authors of the breastfeeding rebuttal should review other credible sources of breastfeeding information rather than just focusing on the AAP. I do not see that any of the authors are practicing clinicians or that they would be experts specifically in health related statistics or the field of lactation. It sounds more like the authors had bad personal experiences with feeding. As a practicing clinician who teaches evidence based medicine I find this editorial to be irresponsible and clearly outside of the scope of the authors expertise. Perhaps reflect on the motivation behind this article. What prompted the response? Self reflection is hard when you believe (or don\'t believe) in something that is so personal. I believe there is a independent national review of the available statistics and clearly more controlled studies need to be conducted. There is a Cochrane Review on Breastfeeding-perhaps you should review that as well.
The authors respond
We agree completely with Dr Sullivan - more controlled studies are needed to examine the benefits of breast feeding versus formula. We also acknowledge that there are many other sources of information. However, we examined the information on the AAP website because that was the source cited in the NYT article and the official organization for pedia-tricians, the source of that most parents turn to. Many claims of benefit made by the AAP outweigh the evidence for those benefits. Scientific rigor, whether in evidence-based medicine, basic science or mathematics, has taught us that association is not causality.
We are three mothers who successfully breast fed our children - that is
not relevant. Our interest in assessing the NYT article was as objective
scientists. Poor science and poor interpretation of science needs to be
pointed out whether it is by a physcian, a statistician or a
pharma-cologist. We are concerned that the AAP is motivated in giving
its recommendations by what they believe (or don't believe) rather than
by the evidence. Rather than responding to the pressure to have
definitive consensus statements in one direction or the other, when
there is a lack of evidence it should be presented as such. The AAP
would do well to follow your example and call for more controlled studies.