Purpose: Psychological factors, such as stress, anxiety and low mood, are widely considered to influence immunity and infection susceptibility in rested individuals. However, whether psychological factors influence the mucosal immune response to endurance exercise and subsequent infection risk remains unknown. In Study 1, we prospectively examined the association between psychological factors, mucosal immunity and respiratory infection risk in response to a marathon race. In Study 2, we further examined the observed association between psychological factors and the mucosal immune response to exercise shown in Study 1, in a rigorously controlled-laboratory setting.
Methods: In Study 1, 406 marathon runners (67% male) consented to providing daily respiratory infection symptom data for two weeks before and after a mountainous marathon race. In Study 2, 45 healthy young adults (51% male) consented to complete exercise (60 min running at 65% V̇O2peak) under laboratory conditions controlling diet, hydration, and time of day. In both studies, measures of anxiety, total mood disturbance and psychological stress were made, and saliva samples were collected pre- and post-exercise and analysed for secretory immunoglobulin A (SIgA). Logistic and linear regressions were performed with covariates including: age; sex; body mass index; respiratory infection pre-marathon; race duration and sleep (Study 1 only).
Results: After accounting for covariates, trait anxiety (odds ratio = 3.2) and total mood disturbance (odds ratio = 3.3) assessed before the marathon were significant risk factors for post-marathon respiratory infection (Study 1; P<0.05). Further, after accounting for covariates, greater levels of trait anxiety, total mood disturbance and psychological stress were also significantly associated with a greater post-marathon reduction in saliva SIgA secretion rate (Study 1; trait anxiety ∆ R2=0.029, total mood disturbance ∆ R2=0.037, psychological stress ∆ R2= 0.044). In a rigorously controlled-laboratory setting, psychological factors were also significantly associated with the saliva SIgA secretion rate response to exercise in men (Study 2; trait anxiety r= -0.55, total mood disturbance r= -0.61, psychological stress r= -0.66, state anxiety r= -0.65).
Conclusion: Psychological factors are prospectively associated with the mucosal immune response to exercise and increased respiratory infection risk after a marathon. Where possible, athletes should take steps to minimise exposure to high stress and anxiety and improve mood to support immune health and infection resistance. Researchers should take account of psychological factors when examining the mucosal immune response to exercise.