Low diversity in oral microbiome may signal risk of depression
NEW YORK: A new large-scale study has found a surprising connection between oral health and mental health: lower diversity of oral bacteria is associated with greater symptoms of depression. Researchers analyzed saliva samples and mental health data from over 15,000 US adults, revealing how the composition of microbes in our mouths may be more deeply linked to our mood than previously believed.
Led by scientists from the NYU Rory Meyers College of Nursing, the study provides compelling evidence that people with less diverse oral microbiomes are more likely to report symptoms of depression—even after accounting for behaviors like smoking, alcohol use, and oral hygiene. The results were published in BMC Oral Health.
Understanding the mouth–mind connection
The human mouth contains between 500 billion to 1 trillion bacteria, forming the second-largest microbial community in the body after the gut. While gut-brain interactions have been widely researched, this study highlights how oral microbiome diversity may also influence mental health.
According to Bei Wu, senior author and vice dean for research at NYU Nursing, the research offers potential to “develop new biomarkers or treatments for mood disorders” by studying oral bacteria.
What the study found
- Lower microbial diversity = higher depression symptoms.
- Lifestyle factors—smoking, drinking, and dental hygiene—impacted both oral bacteria and mood.
- The association persisted even after controlling for common health behaviors.
Researchers used advanced gene sequencing to analyze microbes in saliva and correlated these findings with standardized depression surveys conducted under the CDC’s National Health and Nutrition Examination Survey (NHANES).
What it means for diagnosis and treatment
Though the direction of the relationship isn’t yet clear—whether microbial changes contribute to depression, or depression alters the microbiome—the findings are a step toward using oral microbiome biomarkers in mental health diagnostics.
Wu noted that inflammation and immune system disruptions may be key pathways linking microbial changes to mental health outcomes. However, depression itself may lead to behavioral changes (like poor oral hygiene, diet changes, and increased substance use) that disrupt microbial balance.
“This is part of a broader effort to understand how the oral microbiome influences not only mental health, but also cognitive decline and dementia,” Wu added.
The study emphasizes the need for further investigation into:
- Causal relationships between oral microbes and mental health.
- Preventive dental care as part of mental health management.
- Microbiome-based interventions, such as targeted probiotics or oral health strategies.
For now, maintaining good oral hygiene might do more than just protect your teeth—it could also support your mental well-being.
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