Researchers have found an indication of depression in a slightly unexpected place – the microbiome inside our mouths. The finding opens a new route of inquiry that could lead to novel antidepressant treatments and help other ailments as well.
The human microbiome consists of the millions of microbes that live in and on our bodies. The largest collection of these mostly friendly bugs lies inside our colons where they do everything from our impacting our memory to influencing the expression of genes. A lack of diversity in our gut microbiomes has also been linked to depression.
Now a study led by researchers at New York University has arrived at the same conclusion about depression and the microbiomes in our mouths – the second largest collection of microbes in our bodies.
“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 senior study author Bei Wu.
Wu and her colleagues found that – just like in our guts – the less diverse the microbes are in our mouths, the more prone we are to depression. They also found that excessive drinking and smoking reduced oral microbiome diversity, as did poor oral hygiene and, conversely, some oral care treatments like scaling, root planing and other deep cleansing modalities.
To reach their conclusion, the researchers conducted an analysis of over 15,000 US adults aged 18 and older who had participated in the National Health and Nutrition Examination Survey (NHANES), conducted by the Centers for Disease Control and Prevention. They then combined data gleaned from questionnaires filled out by the participants with gene sequencing conducted on samples of their saliva.
The researchers point out that, while the link between a less diverse oral microbiome and depression was established by this study, it's not clear whether depression affects behaviors that lessen its diversity, or if its lack of diversity brings on depression – or if there's some combination of the two at play.
“It’s possible that the oral microbiome influences depressive symptoms through inflammation or changes to the immune system," said Wu. "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. We need more research to understand the direction and underlying pathways of this relationship.”
Wu also says that analysis of the oral microbiome could lead to novel treatments for other conditions.
“This work is part of a broader effort to understand how the oral microbiome influences not only mental health, but also cognitive decline and the onset of dementia,” she concluded.
The study has been published in the journal BMC Oral Health.
Source: New York University