Less Diverse Oral Microbiome May Be Linked to Depression

A recent study led by researchers at NYU Rory Meyers College of Nursing explores the relationship between the diversity of microbes in the mouth and the risk of depression. The study suggests that a less diverse microbial community in the oral cavity could be associated with symptoms of depression.

Microbial diversity in the mouth

The human mouth is home to between 500 billion and 1 trillion bacteria, making it the second-largest microbial community in the body, after the gut. Research has increasingly linked the health of the oral microbiome to various systemic health conditions, including diabetes and dementia. The oral microbiome's role is thought to be connected to inflammation and immune system disruptions.

Link between oral microbiome and depression

While a connection between gut microbiome diversity and depression has been studied in animal models, little is known about the potential link between the oral microbiome and mood disorders. This study, published in BMC Oral Health , examined data from the National Health and Nutrition Examination Survey (NHANES) to investigate the association between the oral microbiome and depression in humans.

“Having a better understanding of the relationship between the oral microbiome and depression could not only help us learn about the mechanisms underlying depression, but could contribute to the development of new biomarkers or treatments for mood disorders.”

Dr. Bei Wu.

Study methods

Researchers analyzed survey data and biological samples from over 15,000 U.S. adults aged 18 and older, collected between 2009 and 2012. Participants provided saliva samples, and gene sequencing was used to assess the diversity of bacteria present. This data was compared to responses from depression symptom questionnaires.

Findings of the study

The study found that individuals with lower microbial diversity in their oral microbiomes were more likely to report symptoms of depression. Factors such as smoking, alcohol consumption and oral hygiene habits, which can alter the microbial composition in the mouth, were found to influence this relationship.

Potential implications

These findings suggest that the oral microbiome could serve as a potential diagnostic or therapeutic target for depression, although the study does not establish a cause-and-effect relationship. It remains unclear whether a lack of diversity in oral bacteria contributes to depression or whether depression leads to changes in the microbiome, possibly through factors like medication use or changes in diet.

Next steps for research

The study's lead author, Bei Wu, vice dean for research at NYU Rory Meyers College of Nursing, notes that further research is needed to better understand the underlying mechanisms. One possible explanation is that changes in the oral microbiome could influence depressive symptoms through inflammation or immune responses. However, depression itself could lead to behaviors like poor oral hygiene and increased smoking or drinking, which in turn might alter the microbial makeup of the mouth.

This work is part of a larger effort to explore how the oral microbiome affects mental health, including its potential role in cognitive decline and dementia. As research in this area progresses, it could lead to new strategies for preventing and treating mood disorders.

Reference: Qiu X, Xu T, Huang Y, Wei C, Wang L, Wu B. Relationship between depression and oral microbiome diversity: analysis of NHANES data (2009–2012). BMC Oral Health. 2025;25(1):914. doi: 10.1186/s12903-025-06274-x

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