Many athletes consume caffeine for its known ergogenic effects. Since being legitimised by its 2004 removal from the World Anti-Doping Agency prohibited list of substances, caffeine s ability to enhance performance has led to its widespread use amongst the athletic population. However, despite caffeine s prevalence, little research has focused on the effect of caffeine ingestion on immune function both at rest and in response to exercise in humans. Therefore, the aim of this thesis was to investigate the influence of typically-used doses of caffeine (typical daily intake in training and competition doses) on aspects of innate and acquired immunity in response to prolonged exercise.
At rest both a high (6 mg kg-1) and low dose (2 mg kg-1) of caffeine had little effect on antigen-stimulated T (CD4+ and CD8+) or natural killer (NK) lymphocyte activation, while a high dose of caffeine only increased the number of antigen-stimulated NK cells expressing CD69 1 h following caffeine ingestion (Chapter 4). In response to prolonged high intensity continuous cycling both high and low doses of caffeine increased the natural state of activation as well as the antigen-stimulated activation of NK cells 1 h after exercise cessation (Chapters 5 and 6). However, at the same time-point a high dose of caffeine decreased CD4+ and CD8+ cell activation (Chapter 5). One hour after high intensity intermittent shuttle running, a high dose of caffeine attenuated the exercise-induced increase in NK cell activation both in terms of the number of cells expressing CD69 and their geometric mean fluorescence intensity expression of CD69 (Chapter 7). These effects did not occur in response to intermittent exercise when 2 mg kg-1 caffeine was instead ingested in 3 repeated doses throughout the day (Chapter 7).
In conclusion, the findings of this thesis demonstrate the complex actions of caffeine on antigen-stimulated T and NK lymphocyte activation 1 h after prolonged intensive exercise. However, the biological significance of these findings in terms of caffeine s potential to alter an individuals susceptibility to infection following prolonged high intensity exercise are yet to be determined.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.