STATS ARTICLES 2011
Breastfeeding and the Risk of SIDS
Rebecca Goldin Ph.D and Cindy Merrick, July 12, 2011
Is the failure to breastfeed responsible for 400 Sudden Infant Death Syndrome cases a year?
Sudden Infant Death Syndrome (SIDS), sometimes called “crib death,” is defined by the Centers for Disease Control (CDC) as “the sudden death of an infant under 1 year of age which remains unexplained after a thorough case investigation, including performance of a complete autopsy, examination of the death scene, and review of the clinical history.” In a study published in Pediatrics in 2010, Melissa Bartick, MD and Arnold Reinhold, MBA crunched some numbers on correlations between various infant maladies, including SIDS, and breastfeeding in order to estimate a “cost” of not reaching benchmarks for breast feeding rates among women in the United States. Their conclusion: over 400 deaths from SIDS annually are attributable to mothers who failed to adequately breastfeed their infants, amounting to incredible heartache and almost 5 billion dollars of assessed cost.
As mothers who don’t breastfeed their babies have become a frequent target of health scare studies and their attendant media reporting, we took a closer look at these claims. We found that the science is far from conclusive about the role of breastfeeding in preventing SIDS. And, it turns out, the American Academy of Pediatrics (AAP) agrees. It’s time to let the science speak, albeit with a double negative: not breastfeeding is not killing your baby.
SIDS remains a top killer among infants under one year of age in the United States, taking about 2,500 babies per year according to the AAP. And although the direct causes of SIDS are still elusive, some important risk factors have been identified, notably parents’ smoking in the home, and the sleeping position of the baby. The recommendation that babies sleep on their backs has led to a reduction by more than 50 percent of SIDS deaths since 1990. In 2001, SIDS affected .56 per 1,000 live births, down from 1.2 deaths per 1,000 live births in 1992. The numbers have not changed substantially since 2001, according to the Centers for Disease Control. In 2007, the latest year for which data is readily available, the rate was .54 per 1,000 live births.
Yet despite such gains, researchers are anxious to identify ways to reduce this number even further. And so, with good intentions but misguided science, they have made breastfeeding the new panacea.
Let there be no doubt: not breastfeeding and SIDS are correlated. The problem is that breastfeeding is correlated with many other factors as well, any of which could be the “cause” (or “causes”) behind an increased SIDS rate among people who use formula instead of mothers’ milk. These include a variety of social and cultural differences, differences in care, differences in other feeding patterns, differences in sleeping patterns, differences in genetic makeup, differences in home environment, differences in medical care, etc. The question is whether the evidence points to breastfeeding (or mother’s milk) as a preventative factor by itself and independent of all the other factors with which breastfeeding tends to go hand in hand.
The problem is that we cannot take the same people and compare what happens if they nurse with what happens if they use formula. While any one person may decide to breastfeed or not, the decision, when looked at statistically, reflects differences among those who decide to breastfeed or not. For some of these differences, researchers can record the differences and control for them – these include mother’s education, parents’ income, mother’s IQ, smoking status, and mother’s weight, and even baby’s sleeping position. For others, researchers cannot control for them. These include emotional and mental health, cultural norms, the connection between the baby and the mother, and some aspects of the sleep environment.
This makes causal connections extremely difficult for researchers. The question then becomes not whether the research is “air tight,” as observational data can never lead us to conclusions that are 100 percent certain, but rather whether the evidence is strong enough to justify public health initiatives to encourage people into breastfeeding by telling parents that the costs of not nursing could be their baby’s life.
How did Bartick et al attribute 447 infant deaths a year to insufficient breastfeeding? The Bartick study analyzes the costs associated with not nursing; the study itself was not intended to assess or quantify the effects of nursing or not. Rather, the authors claim to take well-established numbers reflected in the literature and to put a dollar amount on the impact. Their claims were not met with a modicum of skepticism by media sources, despite a number of scientifically based doubts on the conclusion.
Bartick’s specific source on the correlation between breastfeeding and SIDS is the 2007 Agency for Healthcare Research and Quality (AHRQ) meta-analysis. This concluded, “a history of breastfeeding was associated with a 36 percent [with a 95 percent confidence interval of 19 to 49 percent] reduction in the risk of SIDS compared to those without a history of breastfeeding.”
Bartick also points to an even further benefit attributable to breastfeeding observed in a 2009 study by Vennemann, et al, who performed one of the largest case-control studies on record. In this, and probably for the first time, both maternal smoking and prone sleeping position – two of the most significant risk factors for SIDS identified thus far - were taken into account (with the greatest accuracy possible for a recall-based data set). The study found a reduction by approximately 50 percent of the odds ratio of SIDS for having ever nursed, compared to babies that were never nursed. Notably, among its results, the Venneman study found that at every age, the odds ratios for SIDS are the same for exclusive breastfeeding at that age versus any breastfeeding. In other words, the protective effect of breastfeeding shown by the study only appears compared to infants who received no breast milk at all. According to Bartick, they used the “conservative” figure of a 36 percent reduction associated with breastfeeding.
In reality, however, this is one of the most aggressive estimates. The AAP has noted that a number of* studies that do not show a positive effect, and that confounders make the associations that have been found weak. Even the Vennemann study acknowledges that there were significant social differences in their cases and controls, and that all the confounders may not have been controlled for. A case in point, the AHRQ pointed to a large study in which not breastfeeding was significantly associated with injury-related death in infants. This observation suggests that there may well be other extremely important confounders that have not been measured, and perhaps could not be measured, such as parental attentiveness.
In addition, Bartick et al’s insistence that the benchmark be the Healthy People 2010 goal of “80% to 90% compliance with medical recommendations” (“6 months of exclusive breastfeeding, with continued breastfeeding for at least 1-2 years of life”), is not supported by the evidence when it comes to SIDS, even using the most aggressive estimates cited in the article. The purported reduction of SIDS risk occurs with any length of breastfeeding at all, and did not increase appreciably for children who were nursed according to the stringent guideline espoused by the authors.
It is certainly possible that SIDS rates will go down if breastfeeding rates go up. And certainly there is limited evidence that breastfeeding has an impact on SIDS. This is why public health professionals and doctors are examining the issue so closely. However, the causal link between not breastfeeding and SIDS is weak enough that the AAP refused to stand behind it. As it put it in its 2005 statement (reaffirmed in 2009), “although breastfeeding is beneficial and should be promoted for many reasons, the [AAP] task force believes that the evidence is insufficient to recommend breastfeeding as a strategy to reduce SIDS.” For Bartick et al to attribute these deaths to not nursing as part of a campaign advertising the costs of not nursing is irresponsible. Without the science, the claims of cost due to not breastfeeding – 447 babies and almost 5 billion dollars in economic loss (as calculated by value of statistical life, VSL) – are like an empty bottle: wanting for real substance.
* Hauck FR, Herman SM, Donovan M, et al. Sleep environment and the risk of sudden infant death syndrome in an urban population: the Chicago Infant Mortality Study. Pediatrics. 2003;111:1207–121
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