Influence of carbohydrate on serum caffeine concentrations following caffeine ingestion
Objectives To examine the effect of a high carbohydrate meal on serum caffeine concentration following caffeine intake. Design Randomised, double-blind, crossover. Methods Fourteen healthy males randomly completed 4 trials, each separated by 5 days. Participants either remained fasted (on 2 occasions) or ingested a high carbohydrate meal (2.0 g kg−1 carbohydrate, 42.4 ± 0.6 kJ kg−1) prior to consuming either 6 or 9 mg kg−1 anhydrous caffeine. Venous blood was sampled for the analysis of serum caffeine at baseline and at 6 time-points over 4 h following caffeine intake. Results Peak caffeine concentration occurred 60 min following ingestion for both the 6 and 9 mg kg−1 fasted (p < 0.001) trials compared to 120 and 180 min following ingestion for the 6 and 9 mg kg−1 fed trials, respectively (p < 0.001). Peak concentration was greater in the 9 mg kg−1 fasted trial than the corresponding fed condition (70 ± 9 μmol L−1 and 56 ± 6 μmol L−1, respectively) and both were greater than the 6 mg kg−1 conditions (44 ± 8 μmol L−1 and 38 ± 8 μmol L−1 for 6 mg kg−1 fasted and fed, respectively). Area under the caffeine curve was significantly greater (p < 0.001) in the 9 mg kg−1 fasted trial (3262 μmol L−1 h−1), whilst areas were lowest in the 6 mg kg−1 fed trial (1644 μmol L−1 h−1). Conclusions A high carbohydrate meal consumed prior to caffeine ingestion significantly reduced serum caffeine concentrations and delayed time to peak concentration. Differences in research findings between caffeine supplementation studies may, at least in part, be related to variations in postprandial timing of caffeine intake. The influence of postprandial timing should be considered when athletes consume caffeine with the aim of enhancing performance.