Effect of a single and repeated dose of caffeine on antigen-stimulated human natural killer cell CD69 expression after high-intensity intermittent exercise

Several studies investigating the effect of caffeine on immune function following exercise have used one large bolus dose of caffeine. However, this does not model typical caffeine consumption. Therefore, the purpose of this study was to investigate whether small repeated doses of caffeine ingested throughout the day would elicit a similar response as one large bolus dose ingested 1 h prior to exercise on antigen-stimulated NK cell CD69 expression following strenuous intermittent exercise. In a randomized cross-over design, 15 healthy males completed six 15 min blocks of intermittent running consisting of maximal sprinting interspersed with less intense running and walking. Participants had ingested either 0 (PLA), 2 mg kg−1 body mass (BM) caffeine on three separate occasions during the day (3× CAF) or one dose of 6 (1× CAF) mg kg−1 BM caffeine, 1 h before exercise. At 1-h post-exercise, the number of antigen-stimulated CD3−CD56+ cells expressing CD69 was lower on 1× CAF compared with PLA [P < 0.05; PLA: 42.0 (34.0) × 106 cells L−1, 1× CAF: 26.2 (25.0) × 106 cells L−1], with values on 1× CAF at this time point remaining close to pre-supplement. 1× CAF tended to attenuate the exercise-induced increase in geometric mean fluorescence intensity of CD69 expression on antigen-stimulated CD3−CD56+ cells 1-h post-exercise [P = 0.055; PLA: 141 (28)%, 1× CAF: 119 (20)%]. These findings suggest that although one large bolus dose of caffeine attenuated the exercise-induced increase in antigen-stimulated NK cell CD69 expression 1 h following strenuous intermittent exercise, this attenuation at no point fell below pre-supplement values and caffeine does not appear to depress NK cell CD69 expression