Laura Panagi, Lydia Poole, Ruth A Hackett, Andrew Steptoe

Positive psychological characteristics in people with type 2 diabetes (T2D) are associated with better health and longevity, and one plausible physiological mechanism involves lower markers of inflammation. Positive affect is related to lower basal inflammatory markers and smaller inflammatory responses to acute stress, but this association in people with T2D remains to be examined. To examine the relationship between happiness and inflammatory markers at baseline and in response to acute stress in people with T2D. One hundred forty people with T2D took part in laboratory-based stress testing. We aggregated daily happiness ratings over 7 days before stress testing. During the laboratory session, participants underwent two mental stress tasks-the mirror tracing and the Stroop task. Blood was sampled at baseline and post-stress (up to 75 min post-stress) to detect plasma interleukin-6 (IL-6), interleukin-1 receptor antagonist (IL-1Ra), and monocyte chemoattractant protein-1 (MCP-1). Associations between happiness and inflammatory markers and responses were analyzed using multivariable linear regressions. Greater daily happiness significantly predicted lower baseline and post-stress IL-6 concentrations, and lower baseline MCP-1, after adjusting for covariates. The association between happiness and reduced basal IL-6 maintained after further controlling for daily sadness. We did not find significant associations between daily happiness and inflammatory responses to acute stress. No associations were detected for IL-1Ra. Happier individuals with T2D have lower inflammatory markers before and after acute stress, albeit independent of stress responsivity. Findings could provide a protective physiological pathway linking daily happiness with better health in people with T2D.