A recent study from Pennsylvania State University found that the oral bacteria of two-year-old children may help predict later overweight. Researchers examined more than 226 children and mothers and showed a link between the composition of the oral microbiota (the community of microorganisms, including beneficial bacteria, that live in the mouth) and childhood obesity.
“One in three children in the United States is overweight or obese,” says Kateryna Makova, a biology lecturer at Penn State and a senior author of the paper. “If we can find early markers of obesity in young children, we can help parents and clinicians take preventive steps.”
The work is part of a larger project involving researchers and clinicians at the Penn State Milton S. Hershey Medical Center called INSIGHT, led by Ian Paul, professor of pediatrics at the medical center, and Leann Birch, professor of foods and nutrition at Georgia State University. The project includes nearly 300 children and asks whether early parenting intervention can prevent obesity—and which biological and social risk factors matter.
“In this study, we show that a child’s oral microbiota at age two is associated with their weight gain over the first two years of life,” Makova says.
The human digestive tract hosts a diverse range of microorganisms, including beneficial bacteria that support normal digestion and the immune system. The microbiota shifts with diet and differs from person to person. Changes in the gut microbiota have been linked to obesity in adults and adolescents, but a potential link between the oral microbiota and weight gain in children had not been studied until now.
“The oral microbiota has been studied in the context of gum disease, which in some cases has itself been linked to obesity,” said Sarah Craig, a postdoctoral researcher in biology and lead author of the paper. “This study examined potential direct links between the oral microbiota and child weight gain. Rather than simply noting whether a child was overweight at age two, we also looked at growth curves over the first two years, which give a fuller picture of growth rate. That approach is very innovative for this kind of research and gives greater statistical power to the associations we tested.”
Among the 226 children studied at Penn State, those with the fastest weight gain—a strong risk factor for childhood obesity—had a less diverse oral microbiota, meaning fewer groups of bacteria. They also had the highest Firmicutes-to-Bacteroidetes ratio: two of the most common bacterial groups in the human microbiota.
“A healthy person usually has many different bacteria in the gut microbiota,” Craig said. “Diversity helps protect against inflammation or harmful bacteria and stabilizes digestive function when diet or environment changes. There is also a balance between Firmicutes and Bacteroidetes; disrupting that balance can impair digestion.”
Lower bacterial diversity and higher Firmicutes relative to Bacteroidetes (the F:B ratio) in the gut have sometimes been observed in adults and adolescents with obesity. The researchers did not see those same associations in the gut bacteria of two-year-olds, which may mean the gut microbiota is not fully established at that age and is still changing rapidly.
“There are usually dramatic shifts in a person’s microbiota during early childhood,” Makova says. “Our results suggest that bacterial signatures of obesity can be detected in the oral microbiota earlier than in the gut. If we can confirm this in other groups of children beyond Pennsylvania, an oral microbiota test could be developed for clinical use to identify children at risk of obesity. That is especially exciting because oral samples are easier to collect than stool samples required for gut analysis.”
Interestingly, children’s weight gain was also associated with the diversity of their mothers’ oral microbiota. That may reflect a shared genetic tendency to develop similar microbiota, or similar diet and environment for mother and child.
“If the oral microbiota is indeed linked to early weight gain, there is some urgency to confirm it so we can help prevent later obesity. We are now using additional techniques to look at specific bacterial strains—not only larger families—in both mothers and children, to see whether particular bacteria influence weight gain and obesity risk.”