NEW YORK, US: Oral diseases and depression are both projected to rise in prevalence over the coming decades, and recent findings suggest the two may be interlinked. A new study conducted by researchers from institutions in the US and China has investigated the association between depressive symptoms and oral dysbiosis, revealing that depression is significantly associated with reduced oral microbiome diversity. While the connection between gut microbiota and mental health has been widely explored, this study underscores the need for further investigation into the role of the oral microbiome in psychiatric conditions.
Depression is a pressing global health issue with well-documented links to systemic health. According to the World Health Organization, approximately 3.8% of the world’s population is affected by depression, with women experiencing the condition around 50% more frequently than men. Despite its prevalence and impact on quality of life, the underlying biological mechanisms of depression remain only partially understood, hindering the development of effective prevention and treatment strategies.
The researchers described their work as a novel approach to mental health research. While the gut microbiome has been extensively studied in this context, they emphasised that the oral microbiome represents the second-largest microbial community in the human body. It contains up to a trillion bacteria and plays a vital role in immune modulation and physiological functions. Alterations in oral microbial composition have previously been linked to cardiovascular, endocrine, immune, neurological and gastrointestinal disorders, as well as a variety of oral pathologies.
This cross-sectional analysis utilised data from the 2009–2012 National Health and Nutrition Examination Survey (NHANES), which included oral rinse samples from 15,018 participants. Of these, nearly half (49.51%) were women, 946 had a clinical diagnosis of depression and the mean age across the sample was 42.2 years.
The study assessed oral microbiome diversity using two commonly applied metrics: alpha diversity, quantified by the observed number of amplicon sequence variants, and beta diversity, measured using Bray–Curtis dissimilarity. The authors found a significant negative correlation between alpha diversity and depressive symptoms. Beta diversity also varied significantly between participants with and without depression, indicating distinct microbial community structures.
While the study could not determine causality—whether depression alters the oral microbiome or vice versa—the researchers concluded that reduced oral microbial diversity is significantly associated with depressive disorders. They suggested that “these findings highlight that oral microbiota could serve as a predictive biomarker for depression. Furthermore, diagnostic and therapeutic approaches based on oral microbiota have great potential for the intervention and management of depressive disorders.”
The study, titled “Relationship between depression and oral microbiome diversity: analysis of NHANES data (2009–2012)”, was published on 5 June 2025 in BMC Oral Health.
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