Review backs role of grape polyphenols in sports performance
A recent review published in the Journal of the International Society of Sports Nutrition suggests that polyphenols in grape products, including juice and supplements made with grape extracts, can be beneficial in managing the oxidative stress associated with long term, high intensity exercise. The review was conducted by researchers associated with an institute and a university in the Basque area of northern Spain.
Oxidative stress studied since 1970s
The researchers noted that it wasn’t until the 1970s that the connection of oxidative stress with long term high intensity exercise was first discovered. The role of reactive oxygen and nitrogen species (RONS, in the authors’ parlance) in muscular adaptation has since been more fully understood. Low levels of these compounds have a beneficial role in gene expression and cell signaling. But too much of these compounds can damage muscle tissue, causing athletes to take a step back in their training. Too much of this oxidative stress for too long can lead to so-called ‘overtraining syndrome’ in which power and aerobic capacity declines even as the athlete puts in more work.
Getting the right amount of antioxidants at the right times from polyphenol-rich botanical extracts is the key to enabling athletes to put in high amounts of work sans muscle damage while at the same time avoiding the blunting of training effects, the authors said.
“The use of antioxidant supplements for ameliorating the exercise-induced RONS has become a current topic as there is considerable evidence that these supplements might not only prevent the toxic effects of RONS, but also blunt their signaling properties responsible for the adaptive responses . While chronic daily use of antioxidant supplements should be avoided, strategic use of these products in and around periods of heavy training/game scheduling is the best approach,” the authors noted.
Benefits of grape polyphenols
To see how grape polyphenols might be used in this way the researchers evaluated a number of papers on the subject. The authors found 12 relevant studies, the earliest being from 2005 with the most recent papers dating to 2019. The studies were about evenly divided between those that used grape beverages and those using polyphenol-rich grape extracts (including both grape skin and grape seed extracts) as the study material. The studies used a variety of high level amateur to elite level athletes competing in cycling, rowing, running and other sports as participants.
“Supplementation with grape polyphenols seems to have a positive effect against oxidative stress. These effects are dependent on the supplement dose, the length of the supplementation period or the polyphenolic profile (total polyphenol content and the distribution among polyphenolic families). Besides, according to several reports, it appears that the type and intensity of exercise can affect the response of the blood antioxidant defense system, just as the training status of the athlete, or the sport discipline. Considering the supplementation dosage in these studies it seems unlikely athletes would gain enough quantity of polyphenols from diet,” the authors noted.
Among the limitations of the noted by the authors is the fairly small body of literature on the subject. In addition, within teh broad category of grape polyphenols, a number of different products were used in the studies that were reviewed, making it difficult to make more than broad conclusions at this point.
“Given the promising evidence, although still limited, more pilot studies on effect of grape polyphenols on the oxidative stress produced by sport should be conducted to determine the optimal concentration, dosage and effect on the oxidative stress for target athletes,” the authors noted.
Source: Journal of the International Society of Sports Nutrition
18, Article number: 3 (2021)
Grape polyphenols supplementation for exercise-induced oxidative stress
Authors: Elejalde E, et al.