Study Finds Why Nicotine Is a Risk for SIDS

It interferes with a brain protein key in breathing

MONDAY, Sept. 9, 2002 (HealthDayNews) -- It's been well documented that smoking during pregnancy increases the risk of sudden infant death syndrome (SIDS), and scientists now think they know why.

For the first time, researchers have shown what nicotine is doing in the brain to cause SIDS, a finding that experts hope will one day lead to screening to determine which babies are at highest risk.

French scientists found that mice who lacked a certain protein in the brain failed to wake up during the brief pauses in breathing that are common during sleep.

Researchers believe the protein, nicotinic acetylcholine receptor (nAChR), is critical in regulating breathing and arousal during sleep. Nicotine targets the protein, interfering with normal function of the receptor and, hence, with breathing.

They looked at mice who had the protein and those who were bred not to have it. The animals were subjected to both normal oxygen and low-oxygen, which was meant to mimic the interruptions in sleep during the night. The normal mice were more easily awakened during periods of low oxygen than were the mutant ones.

When researchers gave nicotine injections to mice who had the protein, they took longer to wake up during periods of low oxygen. The nicotine had no effect, however, on the mice who lacked the protein.

"We've known for quite some time that women who smoke during pregnancy significantly increase the risk for SIDS in their children," said Ted Slotkin, a professor of pharmacology and cancer biology at Duke University Medical Center. "These observational studies have shown nicotine does something that makes us vulnerable to triggers that cause SIDS, but the studies don't say exactly how nicotine would do that. What this paper does is to provide the missing link."

The study appears today in the online version of the Proceedings of the National Academy of Sciences.

SIDS, which used to be called "crib death," is the sudden and unexplained death of a baby 1 year old or younger. It's the leading cause of death of babies ages one month to a year, according to the National Institute of Child Health and Human Development.

Rates of SIDs have fallen dramatically in the last decade. One big reason for the drop is education campaigns that have taught doctors and parents to put babies to sleep on their backs, Slotkin said. Babies who sleep on their stomachs are much more likely to die of SIDS.

"With the success of the 'Back to Sleep' campaigns, it turns out the one remaining major attributable factor to SIDS is maternal smoking," Slotkin said.

About 6,000 babies died of SIDS in 1992, according to the SIDS Alliance. That number fell to 2,583 in 1999 and about 2,100 in 2000, the most recent figures available.

"Some of the decrease is due to putting babies to sleep on their backs, some of it is due to less smoking during pregnancy and around babies, and some of it has to do with removing soft bedding around babies," said Laura Reno, director of public relations and marketing for the SIDS Alliance. "But there is much we still have to do. I know we could get those rates even lower with more education."

Slotkin said by isolating the faulty protein, the study could also help explain why some infants are susceptible to SIDS even if their mothers don't smoke.

"This might give us a handle on what we might look for in genetic screening that would tell us which babies might be vulnerable to SIDS," Slotkin said. "If you can predict who's at risk, you can do better intervention and prevention."

What To Do

For more information about SIDS, visit the National Institute of Child Health & Human Development or the SIDS Alliance.

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