Saliva microbes differ in pregnant women with stress and mental health symptoms

Findings suggest that oral cavity microbes may play a role in maternal mental health and highlight the potential for targeted interventions during pregnancy to improve psychological well-being.

In a recent study published in BMJ Mental Health, scientists from Michigan State University investigated the link between the diversity and composition of oral microbes and mental health symptoms, such as stress, depression, anxiety, and post-traumatic stress disorder or PTSD, during early pregnancy.

The researchers aimed to identify specific differences in the oral cavity microbiome that could be associated with varying mental health symptoms in pregnant women, potentially uncovering new microbial influences on maternal mental health.

Background

Mental health issues, such as anxiety, stress, and depression, are widespread during pregnancy and affect over 15% of expectant mothers globally. These conditions can affect maternal well-being, caregiving abilities, and child development. Biological contributors, such as hormones and inflammation, have been recognized as factors influencing maternal mental health.

However, emerging evidence also suggests that microbial populations in the body, especially in the gut, might impact mental health through interactions with the brain. Changes in gut bacteria have been linked to emotional stress, anxiety, and depression in pregnant and postpartum women, and treatments targeting gut bacteria, such as probiotics, have been effective in reducing these symptoms.

While gut microbes are well-studied, fewer investigations have focused on the oral microbiome and its potential connection to mental health. Exploring the role of oral microbes in maternal mental health could reveal new opportunities for improving psychological well-being during pregnancy.

About the study

The present study enrolled over 200 pregnant women in their second trimester to assess the relationship between the oral microbiome and various mental health symptoms, such as life stress, depression, anxiety, and PTSD. The researchers recruited the participants through community outreach and screened them based on specific criteria such as age, pregnancy week, and mental health status.

Saliva samples were collected from the participants over two days using self-guided kits, stored at home, and later processed for deoxyribonucleic acid (DNA) sequencing. The saliva collection was performed immediately upon waking to avoid contamination from food, drink, or oral hygiene practices.

The microbial composition of the saliva was analyzed through DNA sequencing of the 16S ribosomal ribonucleic acid (rRNA) gene to identify microbial diversity. Samples were processed to extract mitochondrial DNA, amplified using specific primers, and analyzed using the Illumina platform. To assess microbial diversity, the researchers calculated both alpha and beta diversity metrics to examine species richness and community differences, respectively.

Additionally, environmental factors, including smoking and dental conditions, were controlled for in the statistical analysis. The study used linear discriminant and regression analyses to identify microbial associations with mental health symptoms, focusing specifically on the diversity and abundance of microbial communities.

Various statistical methods, such as Kruskal-Wallis tests and permutational analysis of variance (PERMANOVA), were also used to examine the microbial data in relation to mental health. This approach enabled the researchers to isolate microbial differences potentially linked to mental health in pregnant women.

Results

The study found that specific changes in the oral microbiome were associated with higher mental health symptom scores in pregnant women. Women with high levels of trait anxiety or depression had greater microbial diversity within their saliva samples, suggesting that elevated mental health symptoms might correspond with a broader range of oral bacteria. Meanwhile, PTSD symptoms were linked to distinct microbial community structures. 

Additionally, the abundance of specific bacterial types varied among women with high or low mental health symptoms. For example, the study observed higher levels of the bacterial phylum Proteobacteria in women reporting recent life stress, although this association did not extend to negative life events occurring earlier in pregnancy.

Furthermore, the abundance of certain bacterial types, such as Firmicutes, was higher in women with elevated trait anxiety and depression, while Spirochaetes was associated more with depression symptoms. Bacterial species belonging to genera Dialister and Eikenella were found in higher amounts in women with elevated levels of anxiety or depression, while some Eikenella species were linked to PTSD as well.

Conclusions

Overall, the results indicated that pregnant women with mental health symptoms exhibit distinct patterns in their oral microbiomes that vary based on the type and intensity of symptoms.

These findings underscored the need for further research into the role of the oral microbiome, separate from the gut microbiome, in maternal mental health. They suggested that targeting the oral microbiome could support mental health interventions in pregnancy, potentially benefiting both maternal and child health.