In this study, which was conducted between 1998 and 2001, the researchers examined the cases of 333 infants who died of SIDS and 998 control infants who were matched for age and region. In the data analysis, the following variables were controlled: maternal smoking in pregnancy, maternal family status, maternal age at delivery, socioeconomic status of the family, previous live births, birth weight of the infant, bed sharing in the last night, pillow in the infant's bed, additional heating during the last sleep (a hot water bottle in the infant's bed or the bed in front of a heater), position placed to sleep, and pacifier use during the last sleep.
The key variable factor was breastfeeding. The researchers examined exclusive breastfeeding as well as partial breastfeeding and exclusive formula feeding. They found that fewer than 50% of the SIDS cases were breastfed at the age of 2 weeks, and 83% of the controls were breastfed. Fewer than 40% of the SIDS cases were exclusively breastfed at the age of 1 month compared with 72% of the controls. The researchers found that full or even partial breastfeeding provided a 50% reduction in the incidence of SIDS.
Why does breastfeeding protect infants from SIDS? The researchers offered two possible explanations.
- The first is that breastmilk contains immunoglobulin G. The predominance of SIDS deaths occur between 2 and 5 months, the period in which the immunoglobulin G from the mother has worn off, but the infant isn't yet producing a sufficient quantity to be effective. Therefore, the breastfed infant has the advantage of still receiving this very important factor during a time when he is most vulnerable.
- The second theory has to do with the sleep patterns of the breastfed infant versus the formula fed infant. Breastfed infants are more easily aroused.