April 19, 2022 – Each year about 3,400 babies die suddenly and unexpectedly in the U.S. The risk of Sudden Unexpected Infant Death (SUID) varies across demographic groups. Trying to make sense of these disparities, Melissa Bartick, an assistant professor of medicine at Harvard Medical School and an MPH student at Harvard T.H. Chan School of Public Health, looked at one possible explanation—breastfeeding—in a study co-authored with Henning Tiemeier, Sumner and Esther Feldberg Professor of Maternal and Child Health.
Q: What are some of the SUID disparities among demographic groups, and why is the lack of breastfeeding thought to be one possible explanation for these disparities?
A: SUID is the largest cause of post-neonatal death in the U.S., which has one of the highest infant mortality rates among wealthy countries. Among non-Hispanic Black and American Indian/Alaska Native infants, the SUID rate is more than twice as high as the national average of 0.91/1000 live births; among Hispanic infants, it’s well below average; and the rates among Asian American infants are some of the lowest in the world.
There are a lot of reasons why not breastfeeding might put infants at higher risk. Normally throughout history, mothers and infants would sleep together, and the mother would nurse the infant throughout the night. After a feeding, an infant would roll over on their back. Mother and infant would be easily arousable, and their sleep cycles would be synchronized, so if anything threatened the infant’s airway, the mother would wake up and be able to respond. In this era of formula feeding, however, infants sleep more deeply, sleep by themselves, and could be put to sleep their stomachs, all of which could threaten their breathing and increase the risk of death. In addition, non-breastfed infants have higher risk of infections, and that is thought to possibly play a role as well. Since breastfeeding is less common among Black infants, who have a higher rate of SUID, and more common among Hispanic infants, who have a lower rate of SUID, we wondered if breastfeeding could explain that.
Q: How did you go about investigating this—and what did you find?
A: We looked at four years of U.S. birth certificates from the National Center for Health Statistics—over 13 million certificates in all—along with their linked death certificates. The birth certificates list breastfeeding status at discharge along with a whole host of other characteristics about the mother, including whether she smoked, her marital status, her educational status, and insurance status, as well as characteristics about the baby, such as whether the baby was born preterm or low birthweight.
Our study found that breastfeeding rates differed among demographic groups: While overall it was 82% at hospital discharge, for non-Hispanic Black infants it was 69.5%, for American Indian/Alaskan Native infants 75%, for Asian infants 90%, and for Hispanic infants 87%.
We also found that, overall, not breastfeeding at birth was clearly related to increased SUID risk. Even after adjusting for 12 different characteristics about the mothers and infants that we considered, there was still 14% greater odds of SUID in infants who were not breastfed. This result strengthens earlier findings by accounting for many additional maternal and infant risk factors and still showing an association between not breastfeeding and SUID risk.
What we found surprising was that, for non-Hispanic Black infants, not breastfeeding only minimally explained the disparity in SUID risk—only 2.3% of the higher risk was due to not breastfeeding. And among Hispanic infants, their high rates of breastfeeding only minimally explained their lower SUID risk—only 2.1%. We had thought that not breastfeeding would explain more of the racial/ethnic disparity in SUID risk. To our knowledge, this is the first study to examine whether breastfeeding actually accounts for the disparity.
Q: What do you take away from those findings?
A: Well, there are two issues here. One takeaway is that other social or structural risk factors likely play a much larger role than breastfeeding in explaining the disparity in sudden infant death. These factors could include child poverty, food and housing insecurity, and lack of generational wealth, which are legacies of historical trauma and structural racism that affect Black women more than Hispanic women. The other issue is that our study only looked at breastfeeding initiation, but not at longer durations of breastfeeding, so that limitation must be kept in mind.
Of course, it is important to support breastfeeding because it contributes overall to lower infant mortality. But to reduce disparities, it’s important to address social determinants of health that require more political solutions. Otherwise, we cannot truly make a dent in the very high disparities in infant mortality rates in the United States.