The significance of CYP1A2 genotype on caffeine metabolism and exercise performance : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Human Nutrition at Massey University, Manawatu, New Zealand

Abstract

Objective: The objective of this study was to investigate whether a single nucleotide polymorphism (C to A transversion at position -163 downstream of the first transcribed nucleotide) in the enzyme that metabolizes caffeine (CYP1A2), would explain the variability seen in caffeine related responses in endurance exercise performance. In a double blind crossover trial, well trained male endurance athletes (n=11, mean VO2 max 69±4 mL.kg-1.min-1) ingested either caffeine (5 mg.kg-1) or a placebo 60 minutes prior to performing a lab based experimental protocol involving a two hour steady state cycle (70% VO2 max) followed by a 30 minute time trial to measure performance. The rate of caffeine metabolism over seven hours (inclusive of exercise period) was also determined by the HPLC analysis of plasma caffeine and its major metabolites, paraxanthine, theophylline and theobromine. Caffeine metabolism at rest over a similar seven hour period was also determined in the same manner. Results: Caffeine improved endurance performance by 7.1% (p=0.037) compared to a placebo. Caffeine also significantly elevated heart rate during the time trial (p=0.003); and RPE (p=0.010) and VO2 (p=0.047) during steady state exercise. There was no correlation between caffeine or paraxanthine concentrations at the start of the time trial and subsequent performance and the rate of caffeine metabolism was not significantly different between resting or exercising trials. Furthermore there was no significant interaction between caffeine treatment and CYP1A2 genotype on performance or any other variables measured. However there was a trend for carriers of the C allele showing faster metabolism than those homozygous A/A (p=0.097). Conclusions: Caffeine is ergogenic during endurance exercise, however individual responses were variable. In this study this variability could not be explained by CYP1A2 genotype. However the small sample size in this study especially when subjects were divided into genotype groups, makes drawing conclusions difficult.