Do genetics affect caffeine’s ergogenic effects? Original paper

Caffeine is a notable ergogenic (power-output-increasing) aid, with benefits at doses of 3–6 milligrams per kilogram of body mass when taken approximately 60 minutes before exercise. However, there is considerable variability between individuals in its effects. The CYP1A2 gene determines the rate of caffeine metabolism — people with an AA genotype are “fast” metabolizers, whereas those with AC and CC genotypes are “slow” and “ultraslow” caffeine metabolizers, respectively. This randomized crossover trial assessed whether the CYP1A2 genotype modulates the ergogenic effects of caffeine.

Of the 113 competitive male athletes recruited for the study, 102 completed handgrip tests to assess strength, and 97 completed squat jumps and countermovement jumps to assess power. They completed the protocols approximately 30 minutes after ingesting 2 milligrams per kilogram of caffeine, 4 milligrams per kilogram of caffeine, or a placebo, with approximately 7 days between sessions. The investigators collected saliva samples to assess CYP1A2 genotype.

Although caffeine did not improve strength or power compared to placebo, the investigators observed that participants with the CC genotype experienced a 12.8% decrease in handgrip strength after 4 milligrams per kilogram of caffeine compared to the placebo. There were no differences between AC or AA genotypes in handgrip strength and between genotypes in power.

Only 8 of the included participants had the CC genotype, which might limit the generalizability of the findings.