Having a less varied range of microbes in the mouth may be associated with depression, a new study has found.
Researchers compared questionnaires measuring depression symptoms with saliva samples used to identify the microbes present in the mouth. They found that those with less diversity in their oral microbiomes were more likely to present with depressive symptoms.
Further analysis found that factors which affect the oral microbiome such as smoking, drinking and dental care habits all had an effect on depression scores.
The study was conducted by researchers at the NYU Rory Meyers College of Nursing. Vice dean for research and lead study author Bei Wu suggested depression and microbiome diversity may mutually affect one another.
She said: ‘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.’
How could this help people with depression?
Data from more than 15,000 adults collected as part of the National Health and Nutrition Examination Survey (NHANES) was included in the study. This builds on the findings of previous research which found a link between depression and gut microbiome diversity in mice.
The researchers hope that the findings could contribute to both diagnosing and treating depression. Dr Wu said: ‘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.’
However, they stressed that further research was needed to fully understand the two-way relationship between mental health and the microbiome. Dr Wu added: ‘We need more research to understand the direction and underlying pathways of this relationship. 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.’
Can mental health-related oral bacteria be transmitted to others?
This comes as a further study found that anxiety, depression and insomnia levels become more similar in the first six months of marriage due to sharing of oral bacteria.
The mental health of almost 1,750 couples was measured before and after the first six months of marriage. Couples including one partner suffering with anxiety, depression and insomnia were compared to those including two unaffected partners.
Those married to an affected partner scored significantly higher on tests for all three conditions compared to their baseline. This means that their mental illness levels increased and became more similar to those of their spouses.
The composition of the newlyweds’ oral microbiomes also changed significantly in this period, becoming increasingly similar. In particular, the unaffected partner was found to take on the microbiota of their affected spouse.
The authors of the study suggest that oral bacteria transmission occurs through close contact in newlyweds.
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