Association between perceived happiness levels and peripheral circulating pro-inflammatory cytokine levels in middle-aged adults in Japan.

OBJECTIVES: The idea that perceived happiness may be associated with health and well-being is a recent topic of focus. However, the neurobiological mechanisms underlying the positive effects of happiness on psychological and physiological wellness remain obscure. In this study, we attempted to clarify the association between systemic inflammation and happiness.

METHODS: We recruited 160 healthy volunteers for experiment 1 and compared peripheral inflammatory markers, namely the concentrations of pro-inflammatory cytokines in the serum, between perceived high-happiness and low-happiness groups. Subsequently, we recruited 7 romantic couples for experiment 2 and investigated changes in peripheral pro-inflammatory cytokine levels after the evocation of happiness, which was induced by warm physical contact with the partner.

RESULTS: We found that circulating levels of interferon-γ (IFN-γ), which can affect brain functions and induce depressive symptoms, were lower in the high-happiness group than in the low-happiness group. A negative correlation between the levels of perceived happiness and IFN-γ concentrations was also observed. Furthermore, we also found that experimentally induced happiness could reduce peripheral IFN-γ levels.

CONCLUSIONS: These results revealed an association between the perception of happiness and systemic inflammation. Increased happiness may suppress the peripheral circulation of pro-inflammatory cytokines.