A review of: Vennemann, M., Bajanowski, T., Brinkmann, B., Jorch, G., Yucesan, K., Sauerland, C., Mitchell, E., & , . (2009). Does Breastfeeding Reduce the Risk of Sudden Infant Death Syndrome? PEDIATRICS, 123 (3) DOI: 10.1542/peds.2008-2145
In the wake of the recent controversy created by Hanna Rosin’s article “The case Against Breastfeeding,” I decided to discuss a brief but powerful study that was just published in the Journal of the American Academy of Pediatrics. A German team of researchers examined the association between breastfeeding and the risk for sudden infant death syndrome (SIDS).
SIDS is a major public health problem, as it is the leading cause of death for infants in the developed world. Several countries have initiated campaigns to try to raise awareness about factors that have been associated with an increased risk for SIDS. These factors include smoking during
pregnancy, sleeping in the prone position (face down), and bed sharing with an adult. In addition, many studies conducted in the 1990s showed that breastfeeding also lowered the risk for SIDS significantly, which led some countries to add breastfeeding to educational campaigns designed to lower the risks of SIDS. However, these older studies had a number of methodological problems, mainly their tendency to compare “never breastfed” against “any breastfeeding.” That is, most previous studies divided the infants’ feeding history into two discrete categories: those who were never breastfed and those who were breastfed at least some times. This creates a number of problems. For example, it is unknown if the potential “protective” features of breastfeeding is limited to “exclusive breastfeeding” or whether “some” breastfeeding is sufficient to lower the risk of SIDS.
In the current study, the authors examined data from the German Study of Sudden Infant Death Syndrome. The study included 333 infants who died from SIDS in Germany between 1998 and 2001, as well as 988 age-matched controls. The authors examined the history of breastfeeding before the babies’ death and compared them to the history of breastfeeding of the healthy control peers up to the same age.
By two weeks of age only 50% of the SIDS cases were breastfeed. In contrast, by this age, 83% of the healthy babies were breastfed.
By one month of age, only 40% of the SIDS cases were exclusively breastfed compared to 72% of the healthy babies. In addition, 50% of the SIDS cases were not breastfed at all compared to only 17% of the healthy peers. The percentage of both groups that were partially breastfed was the same at around 10%.
Most importantly, during the month before their death, 78% of SIDS babies had not been breastfed, compared to 39% of the healthy babies at the equivalent age. Only 9% of the SIDS babies were exclusively breastfed during this month compared to 34% of the healthy peers. Moreover, during this time, 13% of the SIDS cases were partially breastfed, compared to 28% of the healthy peers.
The authors then controlled for a number of possible confounding (explanatory) variables to determine whether breastfeeding was associated with a reduction in the risk of SIDS. These variables included smoking during pregnancy, maternal age at delivery, socio-economic status, family status, number of other births, birth weight, bed sharing, whether there were pillows in the baby’s bed, sleeping position, and use of pacifiers.
The authors found that breastfeeding (any and exclusively) was associated with a 58% reduction in the risk of SIDS (OR .42 95%CI = .36-.48) when not controlling for the confounds, and a reduction of 31% (aOR .69 95%CI = .57-.84) when controlling for the possible confounding variables. Being exclusively breastfed was associated with a risk reduction of 48% (OR .52 95%CI = .46-.60) unadjusted, and 18% after adjusting for the possible explanatory variables (aOR .82 95%CI = .68-.98).
It is worth noting that while there was no difference between the groups in “partial breastfeeding” at 1 month of age, during the month prior to their death, SIDS cases were significantly less likely to be partially breastfed than the healthy comparison group. In addition, being exclusively breastfed did not seem to provide significantly added benefit from being partially breastfed. It thus appears that it is the absence of any breastfeeding that poses the biggest risk. The authors concluded:
This large study conducted after the major reduction in SIDS mortality adds to the body of evidence showing that breastfeeding reduces the risk of SIDS, and that this protection continues as long as the infant is breastfed. In our study, 73% of the infants died before 6 months of age. The implication of our findings is that breastfeeding should be continued until the infant is 6 months of age and the risk of SIDS is low.
But why is breastfeeding associated with a reduction in the risk of SIDS?
The authors explained that many SIDS cases are believed to be related to dysregulated inflammatory reactions during infections. Many of these cases present respiratory infections prior to their death and inflammatory cytokines (a type of molecule produced by the infection) are associated with respiratory and cardiac dysfunction. So how does breastfeeding help? Breast milk contains immunoglobulin, an antibody that plays a critical role in the human immune system, and has been linked to improved immune functioning in infants (actually children and adults too). So it is likely that breastfeeding reduces the risk of SIDS by enhancing the baby’s immune system and thus reducing the risk of dangerous infection-induced inflammatory reactions.
Finally, a note of caution about this type of epidemiological study and a thought about using the term “risk reduction”. The statistical model used estimates the odds of an infant being in one group or another (the SIDS vs. the Controls) based on the variable(s) in question (in this case breastfeeding). Thus, when we say that there was a risk reduction of 48%, we are extrapolating from a model that is telling us that the chances of being “observed” in the SIDS group decreased by 48% simply by having been breastfed (any or exclusively). We interpret this result as a reflection of a reduction in risk, but technically we can’t tel
l with certainty if breastfeeding would directly lead to such reduction. This is therefore, very similar to a correlation, in that the findings do not imply causation. It is still possible that another factor that is associated with breastfeeding explains why the healthy babies were more likely to be breastfed than the babies who died of SIDS.
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