The researchers are not sure why back sleepers had fewer symptoms than did stomach sleepers. One possibility is that stomach sleepers have higher mouth and throat temperatures than do back sleepers. These higher temperatures may be more favorable to the bacteria involved in colds and otitis media.
"No identified symptom or illness was significantly increased among nonprone (not on the stomach) sleepers during the first six months," the study authors conclude. "These reassuring results may contribute to increased use of the supine (on the back) position for infant sleeping."
In the 1980s, several countries conducted studies that found placing babies to sleep on their backs reduced the risk of SIDS. By 1992, Australia, New Zealand and the United Kingdom already had campaigns in place urging parents and caregivers not to place babies to sleep on their stomachs. The study authors noted that in the U.S. in 1992, roughly 70 percent of U.S. babies were placed to sleep on their stomachs. The NICHD-sponsored Back to Sleep campaign, begun in 1994, urges parents and caregivers to place babies to sleep on their backs to reduce SIDS risk. As of 1998, when the study authors finished their analysis, the percentage of stomach sleeping had declined to 17 percent. By this time, the SIDS rate also dropped by about 40 percent.
In the U.S., however, many physicians and caregivers still have reservations about placing babies to sleep on their backs. For example, some fear that an infant sleeping on his or her back might be more likely to choke on vomit. Others believe that babies would sleep better on their stomachs. The researchers undertook the study to rule out the possibility that U.S. babies would react any differently to back sleeping than did babies in other countries.
Source: National Institutes of Health, May 12, 2003