Emotional states correlate with microbiome variations, scientists find

A recent study published in Psychological Medicine found notable correlations between emotional states, including the way emotions are regulated, and the composition of the gut microbiome. These associations suggest a link between the psychological processes of managing emotions and the types of bacteria present in the gastrointestinal tract, shedding new light on the gut-brain axis.

Our gut microbiome is a complex and dynamic community of trillions of microbes, including bacteria, viruses, and fungi, residing in our gastrointestinal tract. These tiny organisms play a vital role in our overall health, influencing digestion, immunity, and even our moods and mental health.

The gut-brain axis refers to the two-way communication network between the central nervous system (which includes the brain) and the enteric nervous system (which governs the function of the gut). This network is not only a physical link but also a chemical one, as gut microbes produce various substances that can affect brain function.

Previous research has established a connection between emotional states and physical health. Both positive emotions, like happiness, and negative ones, like anxiety or depression, have been linked to health outcomes such as heart disease and obesity. However, the mechanisms underlying these links were not fully understood. Researchers hypothesized that the gut microbiome could be a key player in this relationship, particularly since certain psychiatric conditions are associated with changes in gut microbiota.

In a joint statement, study co-authors Shanlin Ke (a postdoctoral research fellow at Brigham and Women’s Hospital), Yang-Yu Liu (an associate professor at Brigham and Women’s Hospital), Anne-Josée Guimond (a scientific professional at the Institut National d’Excellence en Santé et en Services Sociaux du Québec), and Laura D. Kubzansky (a professor at the Harvard TH Chan School of Public Health) explained the motivation behind the research:

“Both negative (e.g., depression, anxiety) and positive (e.g., happiness, pleasure) manifestations of emotion have been linked with the likelihood of maintaining physical health as well as the risk of developing chronic disease and overall mortality. Emotion regulation, i.e., the strategies individuals use to manage their emotions, may also impact health and help explain why positive and negative emotions are associated with physical health outcomes.”

“The gut–brain axis (i.e., the biochemical signaling between the gastrointestinal tract and the central nervous system) links emotional and cognitive areas in the central nervous system with the gut; this connection allows bidirectional effects whereby the brain can drive changes in the gut environment and alter the microbial composition; and the gut microbiota can, in turn, influence emotional processes.

“In this study, we wanted to examine whether positive and negative emotions, as well as two commonly used strategies to regulate emotion, i.e., cognitive reappraisal (reframing the situation to see it in a more positive light) and emotional suppression (holding back from expressing their negative emotions), would be associated with the gut microbial composition and functional pathways in healthy women,” the researchers explained.

“A previous study observed links between positive (but not negative) emotions and the composition of the gut microbiome in a small sample of healthy Korean adults; we wanted to look at these relationships, as well as relationships with emotion regulation strategies, in a larger sample of U.S. women.”

Conducted as part of the Nurses’ Health Study II, the current study involved 206 female nurses aged between 49 and 67 years. The participants completed detailed online questionnaires assessing their emotional states, including measures of positive and negative emotions, as well as their emotion regulation strategies, like how often they suppress emotions or reframe their thoughts to feel better.

Participants also provided stool samples over a period of about six months. These samples were then analyzed to identify the types and quantities of bacteria present and the metabolic pathways active in the gut microbiome.

“The strengths of our study include the collection of multiple stool samples per participant, shotgun metagenomics sequencing, detailed phenotyping of the participants, and a validated measure of emotion regulation,” the researchers said.

The team of researchers found that the presence and abundance of certain gut bacteria varied with the participants’ emotional states. Those who reported higher levels of positive emotions had different bacterial compositions compared to those who reported higher levels of negative emotions.

For example, specific bacterial species such as Firmicutes bacterium CAG 94 and Ruminococcaceae bacterium D16 were less prevalent in individuals with higher positive emotion scores. In contrast, these same bacterial species were found in greater abundance in participants with higher negative emotion scores. This finding suggests a complex relationship between our emotional wellbeing and the types of bacteria that thrive in our gastrointestinal tract.

In addition, participants who frequently suppressed their emotions had a less diverse microbial community in their gut. A diverse gut microbiome is often linked to better overall health.

Beyond the presence of specific bacterial species, the study also observed associations between emotional states and the metabolic pathways within the gut microbiome. For instance, negative emotions were linked to a lower abundance of metabolic pathways involved in the biosynthesis of pantothenate and coenzyme A (CoA), essential compounds in various metabolic reactions. Similarly, pathways related to adenosine biosynthesis were inversely correlated with negative emotions.

“Our study suggests that emotions and strategies used to regulate emotions are associated with the gut microbial composition,” the researchers told PsyPost. “More specifically, our findings suggest favorable emotional functioning, characterized by higher levels of positive emotions and lower levels of negative emotions, as well as more effective emotion regulation (i.e., greater use of reappraisal and lower use of suppression), are associated with distinct compositional profiles of the gut microbiome at the species level. We also found specific emotion-related factors were linked to microbiome diversity and certain metabolic pathways.”

“These results support and expand upon existing evidence linking emotion and emotion-related factors with the human gut microbiome. Further, these findings shed light on how higher-order psychological processes may affect or be affected by cellular processes in ways that are relevant to health. They may provide a window into understanding how psychosocial factors are linked to physical health and, ultimately, whether such relationships can be modified to improve health. This offers early evidence to suggest future studies on microbiome-targeted interventions (e.g., probiotics) to promote human emotional and physical health.”

While this study offers important insights, it has its limitations. The sample consisted predominantly of White, middle-aged female health professionals, many of whom were on antidepressant medication. This specific demographic could limit the generalizability of the findings to other groups. Furthermore, the study’s design doesn’t allow for conclusions about causality. It’s unclear whether emotional states influence the gut microbiome, or if it’s the other way around, or if a third unmeasured variable is influencing both.

“The generalizability of our findings needs to be further validated by external studies based on larger and more diverse populations, including men and younger individuals from different racial and ethnic groups,” the researchers explained. “Second, while bi-directionality in the association of emotion-related factors with the microbiome is likely, we could not test for causality or directionality in these relationships because we were working with cross-sectional data.”

“Thus, while we used the most rigorous methods available to assess these associations (i.e., accounting for a range of host factors that might affect these associations, including socioeconomic status and body weight, for example), future work using both human interventional studies and animal experiments is needed to ascertain directionality in these associations. Future work may want to evaluate specific emotions (e.g., anxiety, joy) or other strategies for managing emotions in relation to the gut microbiome as well.”

The study, “Gut feelings: associations of emotions and emotion regulation with the gut microbiome in women“, was authored by Shanlin Ke, Anne-Josee Guimond, Shelley S. Tworoger, Tianyi Huang, Andrew T. Chan, Yang-Yu Liu, and Laura D. Kubzansky.

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