Japanese researchers have found that the relationship between inflammatory processes in the body and psychological symptoms—such as depression, anxiety, fatigue, and somatic complaints—depends strongly on individual characteristics. In people with poor emotion regulation or low sleep quality, these associations were significantly stronger, whereas good sleep and well-developed emotional control skills weakened them or even reversed their direction. The study was published in Brain, Behavior, & Immunity – Health (BB&I).

Inflammation is a fundamental immune response to injury or threat. In the short term, it helps the body recover, but chronic systemic inflammation can persist over time and has been linked to various diseases, including mental disorders. Elevated blood levels of inflammatory markers such as C-reactive protein and cytokines have previously been associated with depression, anxiety, and chronic fatigue.

Researchers led by Kao Yamaoka sought to understand why inflammation is accompanied by psychological symptoms in some people but not in others. They hypothesized that emotion regulation, perception of bodily signals, and sleep quality might play key roles.

The study involved 155 healthy adults aged 30 to 59. Participants completed questionnaires assessing emotion regulation, sleep quality, fatigue levels, symptoms of depression and anxiety, stress responses, and somatic complaints, including gastrointestinal symptoms. Blood samples were also collected to measure levels of inflammatory markers.

The analysis showed that among individuals with poor sleep and weak emotional regulation skills, higher levels of inflammation were associated with more pronounced fatigue, depressive and anxiety symptoms, and physical discomfort. In contrast, among those with good sleep quality and effective emotion regulation, these associations were much weaker or absent altogether. In some cases, higher inflammatory markers were not accompanied by any deterioration in well-being.

The influence of the ability to perceive internal bodily signals (interoception) was less pronounced and depended on the specific context. According to the authors, this suggests a more complex role for bodily awareness compared with sleep and emotional regulation.

The researchers emphasized that inflammation itself does not necessarily lead to poorer mental health. Its impact is largely shaped by individual psychological and behavioral factors. Nevertheless, the findings highlight the importance of sleep and emotional resilience as potential protective factors against the negative psychophysiological effects of chronic inflammation.