This post was updated Nov. 18 at 12:56 p.m.

Young people who experienced parental adversity are more likely to have potentially harmful bacteria in their mouth, according to UCLA.

Young people experiencing caregiving adversity – being mistreated by caregivers or having a long separation from them – also have oral microbiomes that are more resilient to stress, according to an August study. The study examined the oral microbiome of children in middle to late childhood and aimed to find a connection between the oral microbiome and mental health, said Naomi Gancz, a psychology doctoral student and corresponding author of the study.

Most of the current research on the psychosocial factors of caregiving adversity have focused on the gut, said Francesca Querdasi, a psychology doctoral student and co-author of the study. While there is some evidence that oral microbiome dysregulation is also linked to higher mental health risk, studies on children are limited, Gancz said.

The study involved 152 children aged six to 16 years old, with 66 participants who have been exposed to significant caregiving adversity in the past, and 86 who have not.

Researchers used a variety of methods to recruit study participants, including advertising the study on social media, Querdasi said.

Researchers then conducted interviews and collected biological samples from the participants that included saliva and hair, said Emily Towner, a psychology doctoral student at the University of Cambridge and co-author of the study.

“We wanted to look at the oral microbiome and cortisol levels to see if … differences in those biological factors could explain why the Caregiving Adversity group seems to be experiencing more health symptoms,” Querdasi said.

27 participants completed in-person data collection prior to COVID-19 considerations shutting down their lab, Towner said, adding that the remaining 126 participants sent their sample collections through mail and used online media to communicate with the researchers.

After collecting samples, researchers examined health symptoms such as fatigue, physical symptoms and internalizing symptoms, Querdasi said.

Researchers also measured hair cortisol, which measures cumulative physiological stress response over several months, Gancz said.

The study found a negative relationship between hair cortisol levels and microbiome diversity among children not exposed to caregiving adversity, suggesting that stress leads to less bacteria being present in their mouth, Querdasi said. However, this relationship did not hold for those who experienced caregiving adversity, she added.

This finding suggests that the oral microbiomes of children who were not exposed to caregiving adversity are more sensitive to recent stress, Querdasi said. In comparison, the oral microbiomes of young people exposed to caregiving adversity were not correlated to recent stress, suggesting that the community of microbes in their mouth may be resilient, she added.

Querdasi said one explanation for this is that if people are exposed to chronic stress, the body responds by decreasing the cells’ response to cortisol levels. Another alternative explanation could be that young people exposed to caregiving adversity have more sleep problems which disrupt both cortisol and the oral microbiome, Querdasi added.

Independently of cortisol, researchers found different levels of bacteria between the group of children who experienced caregiving adversity and the comparison group, Gancz said. The adversity group had slightly lower levels of bacteria and slightly higher levels of Porphyromonas bacteria, which is genetically close to some bacteria that can be linked to periodontal disease, Gancz added.

The study’s findings aim to shed light on the mechanisms by which adversity can affect long-term health, ultimately leading to improved prevention strategies for at-risk young people, Gancz said. She added that the study hopes to shed light on potential disease prevention.

In the future, Gancz said she plans to look at how the relationship between the oral microbiome and mental health changes over time as children grow up, as well as how the oral microbiome relates to the brain.

“Even though there have been decades of research on the microbiome, I think we’re really, really just at the start,” Gancz said.