Sudden Infant Death Syndrome, or SIDS, is the leading cause of death in the United States among infants in their first year of life. If their mothers smoked cigarettes during their pregnancies, the risks to the newborn increase five-fold.

Studies show nicotine is linked to abnormalities in the part of the brain that controls breathing. Most SIDS deaths occur when children are sleeping.

In laboratory experiments, physiology professor Ralph Fregosi and colleagues at the University of Arizona exposed prenatal rats to nicotine and then tested how the newborns responded to low levels of blood oxygen, a factor which can lead to apnea or cessation of breathing.

"We're simulating an environment where the mother would be smoking 30 cigarettes a day -- a fairly heavy smoker, in other words," Fregosi says. "And we find that over the first nine days of life - and remember these are rats - their response is reduced significantly compared to when they were not nicotine - exposed."

Fregosi says the results are relevant to SIDS because a reduced ability to respond to low blood oxygen or high carbon dioxide makes it harder for an infant to reinitiate breathing and break the apnea should an episode occur.