Table 3.
Characteristics of studies included in the meta-analysis.
| Study | Information of participants |
Dosage (mg/kg) |
Exercise mode | Outcome | Conclusion | ||
|---|---|---|---|---|---|---|---|
| Sample size and sex (male/female) |
Genetic ratio A/C |
Age (year) (mean ± SD) |
|||||
| Giersch et al. (2018)22 | 20 participants (20/0) |
8/12 | 25 ± 8 | 6 | 3-km cycling | Caffeine ingestion made a 2.2% improvement | Serum caffeine concentration C > A after 1 h; caffeine improved performance, but no difference between allele types |
| Grgic et al. (2020)23 | 22 trained males (20/0) | 13/9 | 28 ± 5 | 3 | CMJ test; Wingate test |
Caffeine ingestion enhanced power output in the Wingate test and vertical jump height | Caffeine improved performance, but no difference between allele types |
| Guest et al. (2018)13 | 101 athletes (101/0) |
49/52 | 24 ± 5 | 2; 4 | 10-km cycling | Performance increased 4.8% for 2 mg/kg caffeine and 6.8% for 4 mg/kg caffeine in participants with AA; performance decreased 13.7% for 4 mg/kg caffeine in participants with CC | Only those with the A allele improved |
| Guest et al. (2022)44 | 100 athletes (100/0) |
49/51 | 25 ± 4 | 2; 4 | 10-km cycling | 2 mg/kg caffeine decreased completion time by 1.7 min for participants with AA | Only those with the A allele improved |
| Minaei et al. (2022)18 | 16 trained males (16/0) |
6/10 | 22 ± 7 | 6 | Wingate test | Participants with AA improved 5.8% following caffeine ingestion | Only those with the A allele improved |
| Muñoz et al. (2020)15 | 31 handball players (16 /15) |
14/17 | 24 ± 3 | 3 | CMJ test; sprint test; handgrip strength test |
Jump height increased 3.4% for participants with AA and 4.3% for those with the C-allele | A > C when pitching 7 m after caffeine intake |
| Puente et al. (2018)16 | 19 basketball athletes (10/9) | 10/9 | 28 ± 5 | 3 | CMJ test | Caffeine increased jump height 2.9% in participants with AA; no significant effect for those with the C-allele | Only those with the A allele improved |
| Salinero et al. (2017)27 | 21 participants (14/7) |
5/16 | 29 ± 7 | 3 | Wingate test | Caffeine ingestion increased peak power by 1.7% | Caffeine improved performance, but no difference between allele types |
| Sicova et al. (2021)30 | 100 athletes (100/0) |
46/53 | 25 ± 4 | 2; 4 | Wingate test | No difference | Caffeine had no effect, and genes did not modify the effects of caffeine |
| Spineli et al. (2020)29 | 100 adolescents (no mention) | 49/51 | 16 ± 2 | 6 | handgrip strength test; CMJ test; |
No difference | Caffeine improved performance, but no difference on between allele types |
| Womack et al. (2012)17 | 35 cyclists (35/0) |
16/19 | 25 ± 7 | 6 | 40-km cycling | 4.9% decrease in completion time for participants with AA; completion time increased 1.8% in those with the C allele | The A allele showed a greater ergogenic effect |
| Wong et al. (2021)43 | 102 athletes (102/0) |
50/52 | 25 ± 4 | 2; 4 | CMJ test; handgrip strength test | Participants with CC experienced a 12.8% decrease in handgrip strength with 4 mg/kg of caffeine | Handgrip strength in those with the CC genotype declined in response to 4 mg/kg of caffeine |
Abbreviation: CMJ = countermovement jump test.