A diverse and balanced community of microbes in the mouth especially bacteria is essential not just for oral health but may also offer insights into broader health conditions. A recent study from NYU Rory Meyers College of Nursing reveals a link between reduced oral microbial diversity and depression.

With the mouth housing between 500 billion to 1 trillion bacteria the body’s second-largest microbial population after the gut research increasingly highlights the oral microbiome’s role in overall health. Its connection to conditions like diabetes and dementia is believed to stem from inflammation and immune system disruptions.

While previous research in mice has suggested a possible connection between gut bacteria diversity and depression the link between the oral microbiome and depression remains less explored.

Gaining deeper insight into how the oral microbiome relates to depression could enhance our understanding of its underlying mechanisms and support the discovery of new biomarkers or treatments for mood disorders said Bei Wu senior author of the study and vice dean for research at NYU Rory Meyers College of Nursing. The findings were published in BMC Oral Health.

To investigate the link between the oral microbiome and depression researchers analyzed both survey and biological data from the National Health and Nutrition Examination Survey (NHANES) conducted by the CDC. Drawing on data from over 15,000 U.S. adults aged 18 and older collected between 2009 and 2012 the team compared depression symptom questionnaires with saliva samples. They used gene sequencing to identify and assess the diversity of microbes present in the mouth.

Their findings revealed that individuals with lower oral microbiome diversity were more likely to exhibit symptoms of depression. Further analysis indicated that lifestyle factors such as smoking alcohol consumption and oral hygiene each of which can alter the oral bacterial composition also played a role in the observed connection.

These findings point to the potential of the oral microbiome as a tool for diagnosing or treating depression though more research is needed. It remains unclear whether reduced microbial diversity in the mouth contributes to depression if depression causes changes in the oral microbiome or if both influence each other in a bidirectional relationship.

The oral microbiome might impact depressive symptoms through mechanisms like inflammation or immune system alterations explained Wu. On the other hand depression may lead to behavioral changes such as shifts in diet poor oral hygiene increased smoking or alcohol use and certain medications that can in turn affect the microbiome. Further research is essential to clarify the direction and mechanisms of this relationship.

This study is part of a larger initiative to explore how the oral microbiome impacts not just mental health but also cognitive decline and the development of dementia she added.

Source: https://www.nyu.edu/about/news-publications/news/2025/june/depression-oral-microbiome.html