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• Posted May 14, 2024

Smoking During Pregnancy Could Raise Baby's Odds for Obesity Later

Women who smoke during pregnancy run a higher risk of their kids becoming overweight or obese, and researchers now think they know one reason why.

Children born of moms who smoked while expecting tend to have gut bacteria that is significantly different from that of kids whose moms didn't light up, scientists reported recently in the journal Gut Microbes.

It's been known for some time that women who smoke in pregnancy tend to have babies who become overweight children, said co-senior researcher Anita Kozyrskyj, a microbiome epidemiologist and professor of pediatrics at the University of Alberta in Canada.

“We just didn't know how it happened,” Kozyrskyj said in a university news release. “There may be many ways, but in our study we showed one way is by changing the gut bacteria in the infant.”

Obesity currently affects more than 18% of children and teens, up from only 4% back in 1975, researchers said in background notes.

For the study, researchers used data from more than 1,500 children being tracked as part of a long-term study of child development.

The kids' weight was measured at ages 1 and 3, and stool samples were collected at 3 and 12 months of age.

Researchers found that a child's risk of excess weight was associated with higher levels of a type of gut bacteria called Firmicutes, and that smoking while pregnant increased the abundance of the bacteria in the child's gut.

Firmicutes are a normal part of gut bacteria, and they typically increase in all babies shortly after birth, Kozyrskyj said.

“It's just that the increase [in infants of smoking mothers] occurred too soon. The amounts were too high,” Kozyrskyj explained.

High levels of Firmicutes can result in excessive production of a fatty acid called butyrate, but researchers aren't yet sure why too much butyrate might cause a kid to pack on pounds.

“It's not like butyrate is poisonous or anything like that. It's a natural byproduct. We have butyrate levels in our intestines all the time,” Kozyrskyj noted.

Researchers found that kids had higher levels of Firmicutes bacteria even if their mom cut back on smoking or quit partway through pregnancy. Only moms who never smoked or quit smoking prior to pregnancy had kids with normal levels of the bacteria.

They also found that breastfeeding exclusively for the first three months of the baby's life reduced the smoking effect.

Researchers said more studies are needed to both firm up this association and better understand the effect of Firmicutes on weight.

More information

The U.S. Centers for Disease Control and Prevention has more on smoking during pregnancy.

SOURCE: University of Alberta, news release, May 2, 2024