The Effects of Caffeine on Salivary SIgA Concentration During Exercise and the Influence of the CYP1A2 Genotype rs762551

Salivary secretory immunoglobulin A (saliva SIgA or salivary SIgA) is an integral part of mucosal immunity and is often the first to encounter antigens and foreign invaders. Should an individual's salivary SIgA concentration decrease, they could be more susceptible to an upper respiratory tract infection(s) (URTI). Exercise may induce increases or decreases in salivary SIgA concentration depending on the nature of the exercise. Few studies have investigated as to whether caffeine supplementation can influence exercise-induced changes in salivary SIgA. Nine male and two female healthy, recreationally active (VO2 max: 52.18 ± 10.89 ml/min/kg, mean ± standard deviation) participants exercised for 30 minutes on a treadmill comprised of a 2.5 minute warm up, 5 intervals of 4 minutes at 70% VO2 max and 1 minute at 40% VO2 max, and a 2.5-minute cool down 1 hour after consuming either a placebo, a 2 mg/kg of body mass, or a 4 mg/kg of body mass dose of anhydrous caffeine. Saliva samples were taken upon arrival to the lab (initial), 1 hour post caffeine ingestion (pre-exercise), post- exercise, and 30 minutes post-exercise. Saliva was also used to measure osmolality. During analysis, saliva concentration was measured by both absolute concentration and concentration relative to osmolality. Capillary samples were taken to determine participant genotype for CYP1A2 rs762551. A three-way mixed ANOVA showed no significant main effect of condition, condition x time interaction, or genotype interaction (p > 0.05 for all). However, there was a significant main effect for time (p < 0.05). Post hoc analysis revealed a significant difference between salivary SIgA concentration relative to osmolality post-exercise and 30 minutes post-exercise (1.45 ± 0.63 vs. 2.05 ± 0.38 mg/mOsmol; p < 0.05). Post hoc analysis also revealed a significant increase in absolute salivary SIgA concentration post-exercise compared to initial and pre-exercise levels (153.03 ± 18.46 vs. 125.49 ± 3.15 and 153.03 ± 18.46 vs. 114.24 ± 10.88 mg/L). These findings suggests that caffeine does not have any influence on the exercise-induced salivary SIgA response.