Abstract
PURPOSE: Cytochrome P450 is a liver enzyme which plays a key role in caffeine metabolism. A (C/A) single nucleotide polymorphism at intron 1 of the Cytochrome P450 gene influences caffeine metabolism, with individuals possessing the C variant having slower caffeine metabolism and subsequently higher plasma caffeine levels following caffeine ingestion. Thus, this genetic polymorphism could potentially explain variability in responses to caffeine supplementation. The purpose of this study was to determine if this specific CYP1A2 polymorphism influenced the ergogenic effect of caffeine supplementation during short-duration cycling. METHODS: 24 male cyclists (24.9±7.5 yrs, 179.9±9.6 cm, 76.1±13.4 kg) performed two exercise tests to volitional exhaustion on an electrically braked cycle ergometer, at a workload corresponding to 150% of VO2peak. One hour prior to testing subjects ingested either 6 mg/kgBW of caffeine (CAF) or a placebo (PLA), administered in double-blind fashion. DNA was obtained from whole blood samples and genotyping was performed via polymerase chain reaction using allele-specific primers. Subjects were grouped as those homozygous for the A variant (n = 11) and those possessing the C variant (n = 13). RESULTS: Caffeine significantly increased time to exhaustion (p<0.05) in the overall group. There was a strong, but not significant (p = 0.06) tendency for subjects homozygous for the A variant to derive greater performance improvements from caffeine (33%; PLA = 86.1±25.1 s, CAF = 114.5±37.9 s) compared to subjects possessing the C variant (11%; PLA = 86.9±31.0 s, CAF = 96.6±25.4 s). Blood lactate levels were significantly increased by caffeine intake, both at rest (CAF = 1.03±0.33 mmol/L; PLA = 0.75±0.28 mmol/L) and post-exercise (CAF = 7.59±1.04 mmol/L; PLA = 7.13±1.02 mmol/L), independent of genotype. Peak HR was also significantly elevated in the caffeine trials (CAF = 178±11 bpm; PLA = 175±9 bpm), with no influence of genotype. Isometric MVC of the leg-extensors significantly decreased from pre-exercise (525.2±122.3 N) to post-exercise (490.8±116.2 N), with no influence of caffeine or genotype. CONCLUSIONS: Subjects homozygous for the A variant may have a more pronounced ergogenic effect from caffeine during sprint cycling than individuals who possess the C variant.
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