Is purple grape juice effective in improving physical performance and reducing oxidative stress among recreational runners?
Date of publication of the randomized controlled trial: September 2015
Design
Randomized controlled trial (RCT).
Participants
28 runners who train and participate in an amateur way with an aim to improve personal performance (mean age: 42.7 years for intervention group; 36.3 years for control group, 78.6% male). Participants should have at least 1 year of training with frequency of 5 training sessions per week, and should be participating in competitions on a regular basis.
Intervention
Purple grape juice was consumed 10mL per day prior to and immediately after training for 28 days. On the days without training, purple grape juice was consumed during meals.
Comparator
Comparison: Grape juice versus control beverage. Control beverage referred to a carbohydrate-based beverage with the same amount of calories, carbohydrates, and volume as the grape juice.
Major Outcomes
Outcome 1: Running time-to-exhaustion as assessed by an exercise test with constant speed performed at the anaerobic threshold on the 28th day;
Outcome 2: Oxidative stress as assessed by Total Antioxidant Capacity (TAC) on the 28th day;
Outcome 3: Oxidative stress as assessed by serum concentrations of vitamin A on the 28th day;
Outcome 4: Oxidative stress as assessed by serum concentrations of uric acid on the 28th day.
Settings
This study was performed in an outpatient setting.
Comparison    Grape juice versus control beverage
Main Results
Compared to control beverage, grape juice showed a significant increase in running time-to-exhaustion (15.3%, p=0.002). Besides, grape juice exhibited significant increases in TAC (38.7%, p=0.009), vitamin A (11.8%, p=0.016) and uric acid (28.2%, p=0.005) on the 28th day.
Comparison: Grape juice versus control beverage in recreational runners
Outcomes (units) No. of studies (Total number of participants) Mean score /No. of participants Heterogeneity test (I2) Percentage change (%) (95% CI) p value Overall quality of evidence*
Intervention Comparator
1 (min) 1 (28) 101.9/15 68.2/13 Not applicable as there is only 1 study. 15.3 (not reported) 0.002 Moderate
2 (NA) 1 (28) Not reported/15 Not reported/13 Not applicable as there is only 1 study. 38.7 (not reported) 0.009 Moderate
3 (μmol/L) 1 (28) Not reported/15 Not reported/13 Not applicable as there is only 1 study. 11.8 (not reported) 0.016 Moderate
4 (μmol/L) 1 (28) Not reported/15 Not reported/13 Not applicable as there is only 1 study. 28.2 (not reported) 0.005 Moderate
Keys: CI = confidence interval.
Comparison    Grape juice versus control beverage
Main Results
Compared to control beverage, grape juice showed a significant increase in running time-to-exhaustion (15.3%, p=0.002). Besides, grape juice exhibited significant increases in TAC (38.7%, p=0.009), vitamin A (11.8%, p=0.016) and uric acid (28.2%, p=0.005) on the 28th day.
Comparison: Grape juice versus control beverage in recreational runners
Outcomes (units) 1 (min) 2 (NA) 3 (μmol/L) 4 (μmol/L)
No. of studies (Total number of participants) 1 (28) 1 (28) 1 (28) 1 (28)
Mean score /No. of participants Intervention 101.9/15 Not reported/15 Not reported/15 Not reported/15
Comparator 68.2/13 Not reported/13 Not reported/13 Not reported/13
Percentage change (%) (95% CI) 15.3 (not reported) 38.7 (not reported) 11.8 (not reported) 28.2 (not reported)
p value 0.002 0.009 0.016 0.005
Overall quality of evidence* Moderate Moderate Moderate Moderate
Keys: CI = confidence interval.
Conclusion
Benefits
Compared to control beverage, supplementation with purple grape juice showed an ergogenic effect in recreational runners by promoting increased time-to-exhausting, accompanied by reducing oxidative stress. For all outcomes, the overall quality of evidence is moderate. Further research is fairly likely to have an important impact on our confidence in this estimate of effect.
Harms
The authors did not report details of adverse events.
Link to Original Article
https://www.ncbi.nlm.nih.gov/pubmed/26288392
The synopsis is based on the following article:
Toscano LT. Potential ergogenic activity of grape juice in runners. Appl Physiol Nutr Metab. 2015 Sep;40(9):899-906.


* Interpretation of quality assessment results:
• Very low: Further research is most likely to have an important impact on our confidence in this estimate of effect.
• Low: Further research is likely to have an important impact on our confidence in this estimate of effect.
• Moderate: Further research is fairly likely to have an important impact on our confidence in this estimate of effect.
• High: Further research is unlikely to have an important impact on our confidence in this estimate of effect.
• Very high: Further research is most unlikely to have an important impact on our confidence in this estimate of effect.

Details of assessment method can be found at Chung VC, Wu XY, Ziea ET, Ng BF, Wong SY, Wu JC. Assessing internal validity of clinical evidence on effectiveness of CHinese and integrative medicine: Proposed framework for a CHinese and Integrative Medicine Evidence RAting System (CHIMERAS). European Journal of Integrative Medicine. 2015 Aug 31;7(4):332-41.