Emotional clarity modulates the link between inflammation and depression, study finds

A study of adolescents found that individuals with low levels of emotional clarity who also exhibited higher levels of the inflammatory markers interleukin-6 and C-reactive protein were more likely to experience severe symptoms of depression five months later. The paper was published in Brain Behavior and Immunity.

Depression is a mental health disorder characterized by persistent feelings of sadness, hopelessness, and a loss of interest or pleasure in activities. These symptoms interfere with daily life, relationships, and productivity and, in severe cases, may lead to thoughts of self-harm or suicide. Depression can also affect physical health, causing changes in appetite, sleep disturbances, fatigue, and difficulty concentrating. While it is one of the most common mental health disorders, treatment efficacy remains limited, with a large proportion of cases being categorized as treatment-resistant depression.

Some researchers have observed that the behaviors of individuals with depression resemble those of people who are physically ill. These behaviors, referred to as “sickness behaviors,” include fatigue, concentration difficulties, slower motor function, and reduced interest in daily and social activities. When a person is injured or infected, these behaviors reduce energy expenditure on daily activities, allowing the body to focus on healing and limiting the spread of infection. Sickness behaviors are mediated by pro-inflammatory molecules produced by the body.

Given these similarities, many researchers have proposed that pro-inflammatory processes may also play a role in depression. Previous studies have reported an association between elevated levels of inflammatory proteins in the blood and depressive symptoms.

Auburn R. Stephenson and her colleagues sought to explore the relationship between pro-inflammatory proteins in peripheral blood and depressive symptoms. Specifically, they aimed to determine whether emotional clarity moderates this link. Emotional clarity refers to an individual’s ability to accurately identify, understand, distinguish, and describe their own emotions, which is often disrupted in depression.

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The researchers analyzed data collected as part of the Temple University Adolescent Cognition and Emotion Project (Project ACE), a larger longitudinal study investigating the development of depressive disorders in adolescence. Participants were recruited from the greater Philadelphia area through newspaper advertisements and local middle schools.

The current analysis included data from 225 participants, with an average age of 16-17 years. Forty-six percent of the participants were girls.

Participants provided venous blood samples, allowing researchers to measure the levels of five inflammatory markers. This study focused on three markers: C-reactive protein (CRP), TNF-α, and interleukin-6. The researchers combined these data to create an inflammatory composite score representing the participants’ general level of inflammation.

Participants also completed assessments of emotional clarity (the Emotional Clarity Questionnaire) and depressive symptoms (the Children’s Depression Inventory). They provided additional health-related information. Five months after the study began, participants completed a follow-up assessment of depressive symptoms.

The results showed no association between depressive symptoms and inflammation levels at the start of the study. This result was consistent regardless of participants’ levels of emotional clarity. Additionally, there was no association between inflammation levels and depressive symptom severity five months later when the whole sample was analyzed.

However, among the 37% of participants with the lowest levels of emotional clarity, those with higher levels of C-reactive protein and interleukin-6 at the start of the study tended to report more severe depressive symptoms five months later. TNF-α levels were not associated with depression severity, even in this subgroup.

“In a two-wave study of community adolescents, our findings indicate that adolescents with low emotional clarity may be more vulnerable to the effects of heightened inflammatory activity on future depressive symptoms than adolescents with moderate or high emotional clarity. These results highlight the importance of insight into one’s emotions on the relationship between inflammatory activity and depression symptom severity,” the study authors concluded.

This study sheds light on the interplay between psychological and physiological factors in mental health. However, it is important to note that the study’s design does not allow for definitive causal inferences. Additionally, most participants reported depressive symptom levels below the clinical threshold for a depression diagnosis, so the results may not generalize to individuals diagnosed with depressive disorder.

The paper, “Higher inflammatory proteins predict future depressive symptom severity among adolescents with lower emotional clarity,” was authored by Auburn R. Stephenson, Iris Ka-Yi Chat, Allyson T. Bisgay, Christopher L. Coe, Lyn Y. Abramson, and Lauren B. Alloy.