Mucosal immunity provides the first line of defence against Upper Respiratory Tract Infections (URTI). Recent literature suggests that secretory immunoglobulin A (SIgA) constitutes the predominant immunoglobulin isotype in secretions, including saliva. SIgA could be used to help indicate an athlete’s risk of URTI. Athletic training and competitions often occur in hot environments and therefore performing exercise in these conditions may result in reductions in SIgA concentrations and provides a further stress on immune response. The use of caffeine in athletic population has increased in recent years. Caffeine is a central nervous system stimulant found in ordinary foods and beverages and its metabolic and performance effects have been widely reported. However, the effects of caffeine on mucosal immunity in team sport athletes in hot temperatures is currently unknown. Therefore, the purpose of this study was to investigate the effects of caffeine on mucosal immunity in team sport athletes when exercising at high intensities in heat.

In a double-blinded randomised cross-over design, 12 semi- professional team sport athletes completed two trials which consisted of six 3-minute intervals at 108% of their maximal oxygen uptake (VO2 max) interspersed with 2 minutes of brisk walking in a heat chamber, set at 30 oC and 50% relative humidity (RH). VO2 max is the measurement of the maximum amount of oxygen a person can utilise during exercise. It is a common measurement used to establish the aerobic endurance of an athlete prior to or during the course of training. Participants consumed, at a standardised rate, 6mg/kg/BM of caffeine or a placebo pill. Unstimulated saliva samples were collected at baseline, pre-exercise, immediately post exercise and 1-hour post exercise. Caffeine had no significant effects on salivary concentration rate, salivary flow rate and salivary secretion rates in all participants. The decreases in salivary concentration rate and secretion rate were short lived as post exercise values returned to baseline levels. High intensity exercise in heat may cause a transient drop in immune function after caffeine consumption, however, acute ingestion of caffeine in heat in team sport athletes does not appear to influence SIgA following exercise when the open window period is most apparent.

In conclusion, taking an acute dose of caffeine before completing high intensity exercise in heat did not provoke any changes in mucosal immunity or physiological markers in highly trained male athletes. Results showed that athletes can take a moderate dose of caffeine in heat. However, these results should be treated with caution by coaches as well as athletes and should be tested well in advance before trialling it pre-competition or game.