Individual Differences in Environmental Sensitivity and Gut Health

Associations Between Sensitivity and Gastrointestinal Symptoms

Although research findings have not been fully accumulated yet, it has been suggested that environmental sensitivity is associated not only with mental health but also with physical health (1).

Considering the “dark side” of environmental sensitivity, i.e., that susceptible individuals are more negatively affected by stressful environments and stimuli, it seems plausible to assume a positive association between high sensitivity and negative physical symptoms.

In fact, our study (2) involving 863 adults revealed that those with higher self-reported environmental sensitivity (i.e., sensory processing sensitivity) experienced more gastrointestinal symptoms, including acid reflux, indigestion, abdominal pain, diarrhea, and constipation in the past week.

Recent Focus on Brain-Gut-Microbiota Interactions

Over the past decade, there has been a significant increase in studies reporting that psychiatric symptoms such as depression and anxiety are related to the gut and gut microbiota (3, 4).

For example, it has been reported that rats subjected to inevitable electric shocks showed abnormalities in the composition of the intestinal microbiota compared to rats in a control group (5).

In another study, intestinal bacteria collected from the stools of patients with major depression and fed to germ-free mice resulted in behavioral changes similar to depression and anxiety (6).

Although the causal relationship has not been fully elucidated yet, current thinking suggests that the inflammatory and immune responses associated with psychiatric symptoms affect gut function and the composition of the gut microbiota, and that the gut and microbiota also interact with the brain through neuroendocrine and neural pathways (4).

Study Aim and Methods

Given that environmental sensitivity is a concept associated with susceptibility to stressors and heightened neurophysiological responses, it may be related to the brain-gut-microbiota axis. For example, highly susceptible individuals may be at lower risk for psychiatric symptoms if they have higher levels of gut function and microbiota diversity.

We examined whether environmental sensitivity and gut microbiota interact and are associated with biomarkers of psychiatric symptoms (7).

Eighty-eight adults completed a questionnaire to measure environmental sensitivity. Participants’ feces were collected to assess gut microbiota diversity (i.e., observed operational taxonomic units, Shannon, and phylogenetic diversity). In addition, participants’ blood serum and plasma were collected to obtain inflammatory indices (i.e., C-reactive protein and lipopolysaccharide-binding protein), biomarkers of psychiatric symptoms.

Key Findings

Between the two variables, environmental sensitivity was not directly associated with inflammation, but the relationship differed by level of gut microbiota diversity.

Individuals with high environmental sensitivity had higher inflammation when the diversity of their gut microbiota was low. In contrast, no association with inflammation was found when their gut microbiota diversity was high.

In summary, high sensitivity and low gut microbiota diversity may be a risk for heightened psychiatric symptoms. However, for highly susceptible individuals, high gut microbiota diversity may also be a protective factor.

Implications for the Public

Several intervention studies have reported that individuals with high environmental sensitivity are more likely to experience a decrease in depressive symptoms and other problems in response to psychoeducational programs (8, 9). This aspect indicates the “bright side” of sensitivity, i.e., the tendency to benefit from a supportive environment (i.e. vantage sensitivity).

Focusing on this aspect, for highly susceptible individuals, psychoeducational programs that improve diet and the use of nutrients that increase the diversity of the gut microbiota may be helpful not only in improving gut function, but also in improving mental health.