The Durk Pearson & Sandy Shaw®
Life Extension NewsTM
Volume 16 No. 7 • August 2013

Happiness Research

The Effect of Peripheral Circulating Pro-inflammatory Cytokines and Perceived Happiness in Middle-aged Adults in Japan

A recent study1 reports on a possible connection between the level of circulating proinflammatory cytokines and perceived happiness, where higher amounts of one of these cytokines, interferon gamma, was correlated with lower levels of happiness.

Experiment 1 involved 160 healthy volunteers (77 males and 83 females, ranging in age from 19–40 years). The researchers screened the subjects for their perceived level of happiness by taking the Japanese version of the subjective happiness scale (JSHS), using the results to divide the group into high happiness respondents and low happiness respondents. Statistical analysis of the two groups found that the high happiness group had significantly higher scores on the Japanese translated version of the Short-Form 36 Health Survey in general health, vitality, emotional role, and mental health as compared to the low happiness group. “Interestingly, serum concentrations of IFNgamma [interferon gamma] were significantly lower in the high happiness group … than in the low happiness group.”

Experiment 2 involved 7 romantic couples; 7 males and 7 females aged 21–38 years. They were requested to answer a number of questions concerning their feelings of romantic love for their partners using the Passionate Love Scale (PLS), which contained questions such as “Sometimes I can’t control my thoughts; they are obsessively focused on __________.” “I would rather be with __________ than anyone else.” The participants were considered to have relatively passionate love relationships. The couples then spent 1 hour in a room with closed doors in which they could kiss and hug but not have intercourse. (This study gets more interesting the longer it goes on.) This was called a warm contact session, after which the couples were asked questions such as “Did you kiss and hug your partner very much?” and “Did you sense your partner’s love?” The results indicated that there was a lot of warm contact in the warm contact session.

Before the warm contact session, however, participants were requested to evaluate their present happiness and blood samples were drawn. Then, with 1 partner remaining in the closed room, the other partner was moved to a second room where he or she read a book (not a book about romance) for 1 hour with closed doors. After that, a second blood sample was drawn. There was at least a 2 week interval between the two conditions and the order of the two conditions was counterbalanced across couples. Finally (yes, there is a finally) the participants were asked to evaluate their feelings of happiness on a scale of 1 (not at all) to 7 (Yes, extremely): Do you feel happy at present?

The IFNgamma (interferon gamma) concentration decreased significantly after the warm partner contact but did not change in the control condition (reading a book). Moreover, the IFNgamma concentration was lower and health related QOL was higher in individuals with self-perceived high happiness than in those with self-perceived low happiness.

How Interferon Gamma Relates to Happiness

Interferon gamma is a pro-inflammatory cytokine that has been shown to reduce circulating serotonin levels by increasing the activity of indoleamine 2,3-dioxygenase, an enzyme that degrades tryptophan, hence reducing tryptophan available for the brain to convert to serotonin. Reduced brain serotonin levels can result in depression. “… previous studies indicated that circulating pro-inflammatory cytokine levels in individuals with depressive symptoms were higher than those in individuals with no depressive symptoms.”1

The researchers also report that their previous study2 found that “the short form of the serotonin transporter gene-linked polymorphic region, which increases serotonin secretion from presynaptic neurons through reduced serotonin reuptake, also enhances amygdala response to desired persons. When IFNgamma levels decrease, the reactivity to positive stimuli increases, and consequently, the evocation of happiness is enhanced.”

The only question remaining, then, is what would have happened to the happiness score and the IFNgamma levels if the couples had been allowed to have intercourse behind those closed doors. We assume that followup experiments will tie up that loose end. In the meantime, we note that since the couples were left in privacy behind closed doors, there is no way to actually know whether they obeyed the instruction to not have intercourse. We leave it to the reader to consider the implications.


  1. Matsunaga et al. Association between perceived happiness levels and peripheral circulating pro-inflammatory cytokine levels in middle-aged adults in Japan. Neuro Endocrinol Lett. 32(4):458-63 (2011).
  2. Matsunaga et al. Genetic variations in the serotonin transporter gene-linked polymorphic region influence attraction for a favorite person and the associated interactions between the central nervous and immune systems. Neurosci Lett. 468:211-5 (2010).

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