Introduction

The use of humor to reduce stress and improve health by producing changes in the immune system has been the topic of many articles and workshops. However, the effectiveness of humor in moderating the effects of stress on the immune system remains unknown at this time.

Framework

Using Psychoneuroimmunology (PNI) as a framework, an experimental pre-post test study was constructed to determine the effect of a brief period of mirthful laughter on stress and natural killer (NK) cell cytotoxicity.

Subjects

Data from thirty-three healthy adult women was used for this project. Volunteers were pre-screened, then randomly assigned to either the distraction control or the humor group. Subjects in the humor group viewed a humorous video, while subjects in the control group viewed two short video tours.

Method

The variables under investigation were measured as follows: exposure to negative life events -(LES); Stress-Arousal - Stress-Arousal Check List (SACL); Humor Response -Humor Response Scale (HRS). Natural killer (NK) cell cytotoxicity was used as a measure of immune function. Natural killer cell (NK) cytotoxicity was determined using a modification of the chromium release natural killer cell assay. (See reliability study for more information on NK assay)

Humor and Stress

According to the Mann-Whitney U test, stress scores decreased significantly more in the humor group than in the distraction group (U = 215.5 p = 0.004), and scores on the HRS scale significantly correlated with post stress for persons in the humor group. Those persons who laughed more had greater decreases in stress following the humor video.

Laughter and Immune Function

Merely viewing a humorous video did not significantly change NK activity for persons in the humor group, compared to subjects in the distraction group (t = 1.52 p = 0.138). However, mirthful laughter, as indicated by scores on the HRS, significantly correlated with change in NK cytotoxicity (r = 0.744 p = 0.001), and tended to correlate with post NK cytotoxicity for subjects in the humor group (r = .45 p = .070). Subjects who averaged a 25 or above on the humor response scale (HRS), which indicated laughter responses, had significant increases in NK cytotoxicity over their baseline values (mean increase of 15.77 lytic units, t = 2.52 p = 0.037). These subjects also had significantly greater increases in NK activity when compared to the rest of the participants (t = 2.1 p = 0.04).

Stress and Immune Function

Overall, pre stress (r = -37 p = .034) and post stress (r = -.43 p = .012) were the only variables that significantly correlated with Post NK activity for persons in both groups. Lower stress scores correlated with higher natural killer cell cytotoxicity.

Summary

This study supports the PNI proposition - A complementary intervention (use of humor) can reduce stress and enhance or optimize immune function (Solomon 1987). This study documents the following:

• The ability of humor and laughter to reduce self-reported stress levels.
• The beneficial effect of a brief period of mirthful laughter on NK activity in healthy women.
• The relationship between lower stress levels and higher NK activity in all subjects, regardless of which group they were assigned to.

• Lambda Sigma Chapter of Sigma Theta Tau International
• Indiana State University Proposal Incentive Fund
• Indiana State University Research Committee
• Indiana University School of Medicine - Terre Haute Center for Medical Education.


Course available starting Spring 2000