A study involving newlywed couples found that oral bacteria may transfer between spouses and be linked to changes in depression, anxiety, and sleep quality.
Investigators observed that healthy spouses living with a partner who experienced insomnia and mood symptoms showed increased psychological distress and changes in their oral microbiota over 6 months.
The study followed 268 newly married couples. One group included couples in which one partner had insomnia as well as symptoms of depression and anxiety, referred to as the depression-anxiety (DA) phenotype. The other group served as healthy controls.
At baseline, the couples completed standardized assessments on sleep quality, depression, and anxiety. Oral swabs were collected from the tonsils and throat, and saliva samples were taken to measure cortisol.
After 6 months, healthy spouses married to DA-phenotype partners had increased depression and anxiety scores and poorer sleep quality. These effects were more pronounced in women.
Biological changes accompanied the psychological symptoms. Salivary cortisol levels rose in healthy spouses, and their oral microbiota began to resemble that of their affected partners. Bacteria such as Clostridia, Veillonella, Bacillus, and Lachnospiraceae were more abundant in DA-phenotype individuals and appeared to increase in their spouses as well.
The findings suggested that close physical contact and shared environments may facilitate bacterial transmission, which could influence emotional and physical health.
Further analysis linked other bacteria, including Fusobacteria and Spirochaetota, to greater insomnia severity and higher depression and anxiety scores. Statistical models showed strong associations between oral bacterial composition, mood symptoms, and cortisol levels.
While the study didn't prove causation, it presented evidence that oral microbiota may influence emotional health in cohabiting couples. The results pointed to a possible biological mechanism behind shared mental health symptoms, beyond social or behavioral factors.
The investigators recommended further research, including studies in clinical populations and animal models, to clarify the impact of microbiota transmission on mental health and assess its role in other conditions.
The study contributed to growing evidence that human microbiomes—particularly in the mouth—may play a role in mental and emotional well-being, especially in the context of close relationships.
The authors reported no conflicts of interest.
