Factors influencing serum caffeine concentrations following caffeine ingestion

Abstract

Objectives To determine whether differences in training status, body composition and/or habitual caffeine intake influenced serum caffeine concentrations following caffeine ingestion.Design Single-blind.Methods Trained cyclists/triathletes (n=14) and active (n=14) males consumed 6 mg kg(-1) anhydrous caffeine. Peak, total and time to peak serum caffeine concentrations were determined from venous blood samples at baseline and 6 time-points over 4h following intake. Body composition was assessed by dual energy X-ray absorptiometry and habitual caffeine intake by a questionnaire.Results Trained cyclists/triathletes had 16% lower peak caffeine concentrations following caffeine ingestion compared to active individuals, although this was not statistically significant (p=0.066). There was no significant difference between trained cyclists/triathletes and active males in total (p=0.131) or time to peak (p=0.249) serum caffeine concentrations. Fat mass was significantly associated with total (r=0.427, p=0.038) but not peak (r=0.343, p=0.101) or time to peak serum caffeine concentration (β=0.00008, p=0.961). There were no associations between habitual caffeine intake and peak, total or time to peak serum caffeine concentrations.Conclusions Following caffeine ingestion three findings from the study were evident: (1) endurance-trained athletes trended towards lower peak caffeine concentrations compared to active males; (2) higher fat mass was associated with higher concentrations of caffeine in the blood over 4h, and (3) habitual caffeine intake does not appear to influence serum caffeine concentrations. Identification of the optimal conditions to ensure peak availability of caffeine within the blood and/or overcoming some of the variation in how individuals respond to caffeine requires consideration of the training status and body composition of the athlete.