The oral microbiome is associated with stress, adversity, and mental health in young adults.

Acute stress responsivity and early-life adversity are both associated with oral microbiome differences that lead to increased mental and physical health risk. However, the joint association of stress responsivity and early adversity with the oral microbiome is not yet understood. Additionally, while the link between the oral microbiome and cortisol has been investigated, another major component of stress responsivity - the parasympathetic response - has been relatively neglected. Therefore, we examined parasympathetic functioning during an acute stressor, retrospective early adversity, oral microbiome (using the bacterial 16S gene), and anxiety and depression symptoms in 76 undergraduates. Early adversity was associated with lower microbiome diversity. Independently of adversity, parasympathetic withdrawal during the stressor was positively associated with Alysiella, a genus previously linked to latent viral infections. Early adversity and parasympathetic function did not significantly interact. Additionally, depressive symptoms were negatively associated with Butyrivibrio, which produces neuroprotective metabolites. Our findings suggest that childhood adversity and parasympathetic stress response are independently associated with oral microbiome differences, and that the oral microbiome is associated with mental health. By characterizing the associations of the oral microbiome with stress, adversity, and mental health, this study lays important groundwork for future research on psychophysiological causes and outcomes of oral microbiome differences.