Purpose: Prolonged, intensive exercise is associated with a reduction in concentration and secretion of salivary IgA (s-IgA). Saliva composition and secretion are under autonomic nervous system control, and caffeine ingestion, a widespread practice among athletes for its ergogenic properties, is associated with increased sympathetic nervous system activation. Therefore, this study investigated the influence of caffeine ingestion on s-IgA responses to prolonged, intensive exercise.
Methods: In a randomized crossover design, 11 endurance-trained males cycled for 90 min at 70% V̇O2peak on two occasions, having ingested 6 mg·kg−1 body mass of caffeine (CAF) or placebo (PLA) 1 h before exercise. Whole, unstimulated saliva samples were collected before treatment (baseline), preexercise, after 45 min of exercise (midexercise), immediately postexercise, and 1 h postexercise. Venous blood samples were collected from a subset of six of these subjects at baseline, preexercise, postexercise, and 1 h postexercise.
Results: An initial pilot study found that caffeine ingestion had no effect on s-IgA concentration, secretion rate, or saliva flow rate at rest. Serum caffeine concentration was higher on CAF than PLA at preexercise, postexercise, and 1 h postexercise (P < 0.001). Plasma epinephrine concentration was higher on CAF than PLA at pre- and postexercise (P < 0.05). s-IgA concentration was higher on CAF than PLA at mid- and postexercise (P < 0.01), and s-IgA secretion rate was higher on CAF than PLA at midexercise only (P < 0.02). Caffeine ingestion did not affect saliva flow rate. Saliva α-amylase activity and secretion rate were higher on CAF than PLA (main effect for trial, P < 0.05).
Conclusions: These findings suggest that caffeine ingestion before intensive exercise is associated with elevated s-IgA responses during exercise, which may be related to increases in sympathetic activation.