Key Takeaway
CYP1A2 genotype determines caffeine response - AA carriers improve performance (SMD = 0.30), AC carriers see modest gains, but CC "slow metabolizers" get worse (SMD = -0.22).
Summary
This meta-analysis of 13 studies (440 participants) examined whether the CYP1A2 gene - which controls caffeine metabolism speed - actually changes how athletes respond to caffeine supplementation. The results are striking and clinically meaningful.
Fast metabolizers (AA genotype) showed clear performance improvements (SMD = 0.30, p < 0.0001), intermediate metabolizers (AC) saw modest gains (SMD = 0.16, p = 0.022), but slow metabolizers (CC genotype) actually performed worse after caffeine (SMD = -0.22, p < 0.0001). This is one of the clearest examples of nutrigenomics directly affecting supplementation outcomes.
The findings suggest that genetic testing (available through 23andMe and similar services) could meaningfully guide caffeine supplementation strategies for athletes. However, the authors caution that conflicts of interest in some included studies may have influenced the CC genotype results.
Methods
- Systematic review and meta-analysis of 13 studies
- 440 participants stratified by CYP1A2 genotype
- AA genotype (fast metabolizers): n = 233
- AC genotype (intermediate): n = 175
- CC genotype (slow metabolizers): n = 34
- 119 total performance outcomes analyzed
Key Results
- AA genotype: SMD = 0.30 (95% CI: 0.21-0.39), p < 0.0001
- AC genotype: SMD = 0.16 (95% CI: 0.06-0.25), p = 0.022
- CC genotype: SMD = -0.22 (95% CI: -0.44 to -0.01), p < 0.0001
- Dose and timing moderated outcomes only for CC carriers
- Higher doses and later exercise timing improved CC responses
Limitations
- Small sample of CC genotype carriers (n = 34)
- Studies with reported conflicts of interest significantly influenced CC results
- Baseline performance differences between genotype groups not fully controlled
- Most participants were male athletes