A lower diversity of microbes in the mouth—particularly bacteria—is associated with depression, according to a new study led by researchers at NYU Rory Meyers College of Nursing.
An estimated five per cent of adults globally suffer from depression, according to the World Health Organization (WHO). Oral diseases affect nearly 3.7 billion people worldwide, and their prevalence continues to rise due to urbanization and changes in living conditions.
“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,” said Bei Wu, vice-dean for research at NYU Rory Meyers College of Nursing and senior author of the study, published in BMC Oral Health.
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Data from more than 15,000 adults
Researchers used data from over 15,000 U.S. adults aged 18 and older, collected between 2009 and 2012 through the National Health and Nutrition Examination Survey (NHANES), conducted by the U.S. Centers for Disease Control and Prevention. Participants completed questionnaires measuring symptoms of depression and provided saliva samples. Gene sequencing was used to identify microbes in the saliva and measure the diversity of the oral microbiome.
“We need more research to understand the direction and underlying pathways of this relationship.” Dr. Bei Wu, vice-dean for research at NYU Rory Meyers College of Nursing.
The study found that individuals with less diverse oral microbiomes were more likely to report symptoms of depression. Additional analysis revealed that smoking, alcohol use and dental care practices—all of which can alter the composition of oral bacteria—influenced this relationship.
“It’s possible that the oral microbiome influences depressive symptoms through inflammation or changes to the immune system. Conversely, depression can drive changes including dietary intake, poor oral hygiene, increased smoking and drinking, or the use of medications—all of which have the potential to alter the oral microbiome,” said Wu. “We need more research to understand the direction and underlying pathways of this relationship.”
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Part of broader effort
Wu noted the research, conducted alongside study authors Xichenhui Qiu, Ting Xu, Yiqing Huang, Changning Wei and Lina Wang, is part of a broader effort to understand how the oral microbiome may influence not just mental health, but also cognitive decline and dementia.
Previous studies have already linked depression with cognitive impairment and increased risk of dementia. However, the link between depression and oral health remains a largely unexplored area.
Earlier this year, Wu and her team also called for oral health to be recognized as a modifiable risk factor for dementia, alongside others such as hearing loss, high blood pressure and obesity.
The NYU Rory Meyers College of Nursing has received funding from the U.S. National Institutes of Health since the early 2000s to study cognitive decline—including dementia—and its relationship to oral health.