Gut bacteria identified as potential link between maternal smoking and child obesity

It's long been established that babies born to mothers who smoked are more likely to be obese. However, researchers at the University of Alberta believe they're closer to understanding why that happens after discovering high levels of gut bacteria in those children.

A new study, conducted by pediatrics professor Anita Kozyrskyj and published in the March issue of the journal Gut Microbes, found an excess of a bacteria called firmicutes in the gut of infants.

Kozyrskyj said it was already known that smoking during pregnancy increases the chance of children becoming overweight or obese.

"But our study added further to this by showing that the way that this can happen is by changing a gut bacteria composition during infancy," the study's senior author told CBC's Edmonton AM on Thursday.

The study found an increased amount of firmicutes in the gut of infants of mothers who smoked. Although all gut bacteria produce metabolites — end products of bacterial metabolism — the large number of firmicutes produces a larger amount of metabolites.

"And this sets off a chain of reaction, which increases this rapid weight gain," Kozyrskyj said.

LISTEN | How maternal smoking leads to obesity in children:

Other adverse effects of smoking while pregnant are well known. According to Health Canada, babies born to people who smoke while pregnant have low birth weight and an increased risk of sudden infant death syndrome (SIDS). It can also affect growing brains and lungs.

However, the connection between obesity in children and smoking while pregnant has been studied more extensively since the 1990s.

According to the Public Health Agency of Canada, as of 2017, 30 per cent of children aged five to 17 are overweight or obese in the country.

Obesity in children can lead to a higher risk of chronic diseases such as asthma, heart disease and Type 2 diabetes.

The three-year study was conducted in Edmonton, Vancouver, Winnipeg and Toronto between 2009 to 2012. It looked at nearly 1,600 babies from birth to age three.

Kozyrskyj said they found that the risk for obesity was still high even if mothers reduced or stopped smoking during pregnancy.

"But if the mother had quit prior to pregnancy, there was no greater risk," she said.

The study also found that babies that were exclusively breastfed — even if they were born to mothers who smoked — did not have the same risk of obesity as formula-fed babies.

Although the study has found gut bacteria to be a common denominator between overweight children and mothers who smoke, more research is needed to confirm that the firmicutes are the exact cause, Kozyrskyj said.